2.4Activity布局绘制

目录介绍

  • 01.Activity布局加载简介
  • 02.handleResumeActivity
  • 03.WindowManager作用
    • 3.1 mWindowManager属性
    • 3.2 WindowManagerImpl介绍
  • 04.requestLayout介绍
    • 4.1 requestLayout方法
    • 4.2 scheduleTraversals()
  • 05.performTraversals()方法
    • 5.1 performMeasure测量
    • 5.2 performLayout布局
    • 5.3 performDraw绘制
  • 06.Activity布局绘制总结
  • 07.Activity布局绘制流程图

01.Activity布局加载简介

  • Activity是通过Window来控制界面的展示的，一个Window对象就是一个窗口对象，而每个Activity中都有一个相应的Window对象，所以说一个Activity对象也就可以说是一个窗口对象，而Window只是控制着界面布局文件的加载过程，那么界面布局文件的绘制流程是如何的呢？

02.handleResumeActivity

  • Android体系在执行Activity的onResume方法之前会回调ActivityThread的handleResumeActivity方法：
    final void handleResumeActivity(IBinder token,
    boolean clearHide, boolean isForward, boolean reallyResume) {
    ...
    if (r.window == null && !a.mFinished && willBeVisible) {
        r.window = r.activity.getWindow();
        View decor = r.window.getDecorView();
        decor.setVisibility(View.INVISIBLE);
        ViewManager wm = a.getWindowManager();
        WindowManager.LayoutParams l = r.window.getAttributes();
        a.mDecor = decor;
        l.type = WindowManager.LayoutParams.TYPE_BASE_APPLICATION;
        l.softInputMode |= forwardBit;
        if (a.mVisibleFromClient) {
            a.mWindowAdded = true;
            wm.addView(decor, l);
        }

    // If the window has already been added, but during resume
    // we started another activity, then don't yet make the
    // window visible.
    }
    ...
    // The window is now visible if it has been added, we are not
    // simply finishing, and we are not starting another activity.
    if (!r.activity.mFinished && willBeVisible
            && r.activity.mDecor != null && !r.hideForNow) {
        if (r.newConfig != null) {
            r.tmpConfig.setTo(r.newConfig);
            if (r.overrideConfig != null) {
                r.tmpConfig.updateFrom(r.overrideConfig);
            }
            if (DEBUG_CONFIGURATION) Slog.v(TAG, "Resuming activity "
                    + r.activityInfo.name + " with newConfig " + r.tmpConfig);
            performConfigurationChanged(r.activity, r.tmpConfig);
            freeTextLayoutCachesIfNeeded(r.activity.mCurrentConfig.diff(r.tmpConfig));
            r.newConfig = null;
        }
        if (localLOGV) Slog.v(TAG, "Resuming " + r + " with isForward="
                + isForward);
        WindowManager.LayoutParams l = r.window.getAttributes();
        if ((l.softInputMode
                & WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION)
                != forwardBit) {
            l.softInputMode = (l.softInputMode
                    & (~WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION))
                    | forwardBit;
            if (r.activity.mVisibleFromClient) {
                ViewManager wm = a.getWindowManager();
                View decor = r.window.getDecorView();
                wm.updateViewLayout(decor, l);
            }
        }
        r.activity.mVisibleFromServer = true;
        mNumVisibleActivities++;
        if (r.activity.mVisibleFromClient) {
            r.activity.makeVisible();
        }
    }

    if (!r.onlyLocalRequest) {
        r.nextIdle = mNewActivities;
        mNewActivities = r;
        if (localLOGV) Slog.v(
            TAG, "Scheduling idle handler for " + r);
        Looper.myQueue().addIdleHandler(new Idler());
    }
    r.onlyLocalRequest = false;

    // Tell the activity manager we have resumed.
    if (reallyResume) {
        try {
            ActivityManagerNative.getDefault().activityResumed(token);
        } catch (RemoteException ex) {
        }
    }
    ...
}
    • 可以看到在在获取了Activity的Window相关参数之后执行了r.activity.makeVisible()方法，看样子这个就是Activity的显示方法
  • 这里我们来具体看一下makeVisible方法的具体实现逻辑：
    void makeVisible() {
    if (!mWindowAdded) {
        ViewManager wm = getWindowManager();
        wm.addView(mDecor, getWindow().getAttributes());
        mWindowAdded = true;
    }
    mDecor.setVisibility(View.VISIBLE);
}
    • 首先判断成员变量mWindowAdded是否为true，可以发现mWindowAdded成员变量只有在执行之后才能赋值为true，所以这里的代码的主要逻辑是该if分支只能执行一次。
    • 这里的ViewManager对象是通过getWindowManager()方法获取的。
  • 这个方法主要作用
    • 是将mDecor给显示到界面上

03.WindowManager作用

3.1 mWindowManager属性

  • 接着上面进行分析。

  • 来看一下getWindowManager()方法的具体实现:

    public WindowManager getWindowManager() {
    return mWindowManager;
}
    • 好吧，原来就是返回的Activity的mWindowManager的成员变量，那么这个mWindowManager的成员变量是什么时候赋值的呢？在Activity的attach方法方法中初始化了Activity的相关成员变量，这里也包括了mWindowManager，我们来看一下mWindowManager的赋值过程：
    mWindowManager = mWindow.getWindowManager();

  • 那么这里的Window对象的mWindowManager成员变量是具体如何赋值的？

    public void setWindowManager(WindowManager wm, IBinder appToken, String appName,
        boolean hardwareAccelerated) {
    mAppToken = appToken;
    mAppName = appName;
    mHardwareAccelerated = hardwareAccelerated
            || SystemProperties.getBoolean(PROPERTY_HARDWARE_UI, false);
    if (wm == null) {
        wm = (WindowManager)mContext.getSystemService(Context.WINDOW_SERVICE);
    }
    mWindowManager = ((WindowManagerImpl)wm).createLocalWindowManager(this);
}
    • 可以发现mWindowManager=((WindowManagerImpl)vm).createLocalWindowManager(this)原来是在这里赋值的，所以一个Activity对应这一个新的Window，而这个Window对象内部会对应着一个新的WindowManager对象。

  • 接着往下看，那么createLoclWindowManager方法是如何实现的呢？

    public WindowManagerImpl createLocalWindowManager(Window parentWindow) {
    return new WindowManagerImpl(mDisplay, parentWindow);
}
    • 原来是new出了一个WindowManagerImpl对象，所以回到我们的Activity的makeVisible方法，ViewManager获取的是一个WindowManagerImpl对象，所以Window对象内部的WindowManager对象其实都是一个WindowManagerImpl的实例，都是而且从继承关系上可以看到：WindowManagerImpl --> WindowManager --> ViewManager;

3.2 WindowManagerImpl介绍

  • 继续往下看：
    wm.addView(mDecor, getWindow().getAttributes());
    • 这里的mDector成员变量，我们知道，它是Activity的界面根View，而getWindow.getAttrbutes方法是windowManager中定义的Params内部类，该内部类定义了许多的Window类型，由于这里的vm是WindowManagerImpl的实例。
  • 我们来看一下这里的addView的具体实现：
    @Override
public void addView(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
    applyDefaultToken(params);
    mGlobal.addView(view, params, mDisplay, mParentWindow);
}
  • 然后我们具体看一下mGlobal.addView方法，这里的mGlobal是一个WindowManagerGlobal的单例对象，WindowManagerGlobal是Window处理的工具类，那么WindowManagerGlobal的addView具体是如何实现的呢?
    public void addView(View view, ViewGroup.LayoutParams params,
        Display display, Window parentWindow) {
    ...
    ViewRootImpl root;
    View panelParentView = null;

    synchronized (mLock) {
        // Start watching for system property changes.
        if (mSystemPropertyUpdater == null) {
            mSystemPropertyUpdater = new Runnable() {
                @Override public void run() {
                    synchronized (mLock) {
                        for (int i = mRoots.size() - 1; i >= 0; --i) {
                            mRoots.get(i).loadSystemProperties();
                        }
                    }
                }
            };
            SystemProperties.addChangeCallback(mSystemPropertyUpdater);
        }

        int index = findViewLocked(view, false);
        if (index >= 0) {
            if (mDyingViews.contains(view)) {
                // Don't wait for MSG_DIE to make it's way through root's queue.
                mRoots.get(index).doDie();
            } else {
                throw new IllegalStateException("View " + view
                        + " has already been added to the window manager.");
            }
            // The previous removeView() had not completed executing. Now it has.
        }

        // If this is a panel window, then find the window it is being
        // attached to for future reference.
        if (wparams.type >= WindowManager.LayoutParams.FIRST_SUB_WINDOW &&
                wparams.type <= WindowManager.LayoutParams.LAST_SUB_WINDOW) {
            final int count = mViews.size();
            for (int i = 0; i < count; i++) {
                if (mRoots.get(i).mWindow.asBinder() == wparams.token) {
                    panelParentView = mViews.get(i);
                }
            }
        }

        root = new ViewRootImpl(view.getContext(), display);

        view.setLayoutParams(wparams);

        mViews.add(view);
        mRoots.add(root);
        mParams.add(wparams);
    }

    // do this last because it fires off messages to start doing things
    try {
        root.setView(view, wparams, panelParentView);
    } catch (RuntimeException e) {
        // BadTokenException or InvalidDisplayException, clean up.
        synchronized (mLock) {
            final int index = findViewLocked(view, false);
            if (index >= 0) {
                removeViewLocked(index, true);
            }
        }
        throw e;
    }
}
  • 可以发现在WindowManagerGlobal中存在着三个数据列表：
    private final ArrayList<View> mViews = new ArrayList<View>();
private final ArrayList<ViewRootImpl> mRoots = new ArrayList<ViewRootImpl>();
private final ArrayList<WindowManager.LayoutParams> mParams =
            new ArrayList<WindowManager.LayoutParams>();
    • 其中mViews主要用于保存Activity的mDector也就是Activity的根View，
    • 而mRoots主要用于保存ViewRootImpl，
    • mParams主要用于保存Window的LayoutParams，WindowManagerGlobal主要作为WindowManagerImpl的辅助方法类，用于操作View组件。
  • 最后我们调用了root.setView方法，这个方法很重要我们就是在这里实现了我们的root与ViewRootImpl的关联的，除了实现了mDector与ViewRootImpl的相互关联，我们还调用了requestLayout方法，这里我们看一下setView方法的具体实现：
    public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {
    ...
    requestLayout();
    ...
}
  • 可以看到，在方法体中又调用了requestLayout方法，这个方法其实就是调用执行重绘的请求，我们来看一下这个requestLayout方法具体实现：
    @Override
public void requestLayout() {
    if (!mHandlingLayoutInLayoutRequest) {
        checkThread();
        mLayoutRequested = true;
        scheduleTraversals();
    }
}
  • 可以看到这里有一个checkThread方法，这个方法是检查当前线程的方法，若当前线程非UI线程，则抛出非UI线程更新UI的错误：
    void checkThread() {
    if (mThread != Thread.currentThread()) {
        throw new CalledFromWrongThreadException(
                "Only the original thread that created a view hierarchy can touch its views.");
    }
}
    • 相信大家平时在编程的过程中肯定会遇到过这个错误，ViewRootImpl是具体更新View的管理类，所有关于View的更新操作都是在这里执行的，自然而然的对于更新线程的检测是在这个类中添加的，一般在更新UI的时候都会调用这个方法用于检测当前执行更新UI的线程是否是UI线程，否则就会抛出这个异常。

04.requestLayout介绍

4.1 requestLayout方法

  • 继续回到我们的requestLayout方法，这里又调用了scheduleTraversales方法，我们来看一下这个方法的具体实现：
    @Override
public void requestLayout() {
    if (!mHandlingLayoutInLayoutRequest) {
        checkThread();
        mLayoutRequested = true;
        scheduleTraversals();
    }
}

4.2 scheduleTraversals()

  • 然后看scheduleTraversales方法
    void scheduleTraversals() {
    if (!mTraversalScheduled) {
        mTraversalScheduled = true;
        mTraversalBarrier = mHandler.getLooper().getQueue().postSyncBarrier();
        mChoreographer.postCallback(
                Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null);
        if (!mUnbufferedInputDispatch) {
            scheduleConsumeBatchedInput();
        }
        notifyRendererOfFramePending();
        pokeDrawLockIfNeeded();
    }
}
    • 这里mChoreographer.postCallback，内部会调用一个异步消息，用于执行mTraversalRunnable的run方法，这个mTraversalRunnable是一个Runnable对象
  • 我们来看一下mTraversalRunnable类的定义：
    final class TraversalRunnable implements Runnable {
    @Override
    public void run() {
        doTraversal();
    }
}
  • 在TraversalRunnable类的run方法中调用了doTraversal方法，我们来看一下这个方法的具体实现逻辑：
    void doTraversal() {
    if (mTraversalScheduled) {
        mTraversalScheduled = false;
        mHandler.getLooper().getQueue().removeSyncBarrier(mTraversalBarrier);

        if (mProfile) {
            Debug.startMethodTracing("ViewAncestor");
        }

        performTraversals();

        if (mProfile) {
            Debug.stopMethodTracing();
            mProfile = false;
        }
    }
}
    • 好吧，其内部又回调了方法performTraversals方法

05.performTraversals()方法

  • 这个方法就是整个View的绘制起始方法，从这个方法开始我们的View经过大小测量，位置测量，界面绘制三个逻辑操作之后就可以展示在界面中了。
    private void performTraversals() {
    ...
    // 执行View组件的onMeasure方法，主要用于测量View
        if (!mStopped || mReportNextDraw) {
            boolean focusChangedDueToTouchMode = ensureTouchModeLocally(
                    (relayoutResult&WindowManagerGlobal.RELAYOUT_RES_IN_TOUCH_MODE) != 0);
            if (focusChangedDueToTouchMode || mWidth != host.getMeasuredWidth()
                    || mHeight != host.getMeasuredHeight() || contentInsetsChanged) {
                int childWidthMeasureSpec = getRootMeasureSpec(mWidth, lp.width);
                int childHeightMeasureSpec = getRootMeasureSpec(mHeight, lp.height);

                if (DEBUG_LAYOUT) Log.v(TAG, "Ooops, something changed!  mWidth="
                        + mWidth + " measuredWidth=" + host.getMeasuredWidth()
                        + " mHeight=" + mHeight
                        + " measuredHeight=" + host.getMeasuredHeight()
                        + " coveredInsetsChanged=" + contentInsetsChanged);

                 // Ask host how big it wants to be
                performMeasure(childWidthMeasureSpec, childHeightMeasureSpec);

                // Implementation of weights from WindowManager.LayoutParams
                // We just grow the dimensions as needed and re-measure if
                // needs be
                int width = host.getMeasuredWidth();
                int height = host.getMeasuredHeight();
                boolean measureAgain = false;

                if (lp.horizontalWeight > 0.0f) {
                    width += (int) ((mWidth - width) * lp.horizontalWeight);
                    childWidthMeasureSpec = MeasureSpec.makeMeasureSpec(width,
                            MeasureSpec.EXACTLY);
                    measureAgain = true;
                }
                if (lp.verticalWeight > 0.0f) {
                    height += (int) ((mHeight - height) * lp.verticalWeight);
                    childHeightMeasureSpec = MeasureSpec.makeMeasureSpec(height,
                            MeasureSpec.EXACTLY);
                    measureAgain = true;
                }

                if (measureAgain) {
                    if (DEBUG_LAYOUT) Log.v(TAG,
                            "And hey let's measure once more: width=" + width
                            + " height=" + height);
                    performMeasure(childWidthMeasureSpec, childHeightMeasureSpec);
                }

                layoutRequested = true;
            }
        }
    }
	...
	// 主要用于测量View组件的位置
	...
    final boolean didLayout = layoutRequested && (!mStopped || mReportNextDraw);
    boolean triggerGlobalLayoutListener = didLayout
            || mAttachInfo.mRecomputeGlobalAttributes;
    if (didLayout) {
        performLayout(lp, desiredWindowWidth, desiredWindowHeight);

        // By this point all views have been sized and positioned
        // We can compute the transparent area

        if ((host.mPrivateFlags & View.PFLAG_REQUEST_TRANSPARENT_REGIONS) != 0) {
            // start out transparent
            // TODO: AVOID THAT CALL BY CACHING THE RESULT?
            host.getLocationInWindow(mTmpLocation);
            mTransparentRegion.set(mTmpLocation[0], mTmpLocation[1],
                    mTmpLocation[0] + host.mRight - host.mLeft,
                    mTmpLocation[1] + host.mBottom - host.mTop);

            host.gatherTransparentRegion(mTransparentRegion);
            if (mTranslator != null) {
                mTranslator.translateRegionInWindowToScreen(mTransparentRegion);
            }

            if (!mTransparentRegion.equals(mPreviousTransparentRegion)) {
                mPreviousTransparentRegion.set(mTransparentRegion);
                mFullRedrawNeeded = true;
                // reconfigure window manager
                try {
                    mWindowSession.setTransparentRegion(mWindow, mTransparentRegion);
                } catch (RemoteException e) {
                }
            }
        }

        if (DBG) {
            System.out.println("======================================");
            System.out.println("performTraversals -- after setFrame");
            host.debug();
        }
    }
    ...
    // 主要用于View的绘制过程
    ...
    if (!cancelDraw && !newSurface) {
        if (!skipDraw || mReportNextDraw) {
            if (mPendingTransitions != null && mPendingTransitions.size() > 0) {
                for (int i = 0; i < mPendingTransitions.size(); ++i) {
                    mPendingTransitions.get(i).startChangingAnimations();
                }
                mPendingTransitions.clear();
            }

            performDraw();
        }
    } else {
        if (viewVisibility == View.VISIBLE) {
            // Try again
            scheduleTraversals();
        } else if (mPendingTransitions != null && mPendingTransitions.size() > 0) {
            for (int i = 0; i < mPendingTransitions.size(); ++i) {
                mPendingTransitions.get(i).endChangingAnimations();
            }
            mPendingTransitions.clear();
        }
    }

    mIsInTraversal = false;
}
  • 可以看到在方法performTraversals方法，我们调用了performMeasure，performLayout，performDraw三个方法，这几个方法主要用于测量View组件的大小，测量View组件的位置，绘制View组件；
    • 即：测量大小 --> 测量位置 --> 绘制组件

5.1 performMeasure测量

  • 好吧，这里我们调用了performMeasure方法，我们先看一下performMeasure方法的具体实现：

    private void performMeasure(int childWidthMeasureSpec, int childHeightMeasureSpec) {
    Trace.traceBegin(Trace.TRACE_TAG_VIEW, "measure");
    try {
        mView.measure(childWidthMeasureSpec, childHeightMeasureSpec);
    } finally {
        Trace.traceEnd(Trace.TRACE_TAG_VIEW);
    }
}

  • 可以看到在performMeasure方法中我们又调用了mView的measure方法，这里的mView就是我们一开始的Activity的mDector根组件，这里的measure方法就是调用的mDector组件的measure方法：

    public final void measure(int widthMeasureSpec, int heightMeasureSpec) {
    ...
    onMeasure(widthMeasureSpec, heightMeasureSpec);
    ...
}

  • 在View的measure方法中，又调用了onMeasure方法，由于我们的mDector对象是一个FrameLayout，所以这里的onMeasure执行的是FrameLayout的onMeasure方法：

    @Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    int count = getChildCount();

    final boolean measureMatchParentChildren =
            MeasureSpec.getMode(widthMeasureSpec) != MeasureSpec.EXACTLY ||
            MeasureSpec.getMode(heightMeasureSpec) != MeasureSpec.EXACTLY;
    mMatchParentChildren.clear();

    int maxHeight = 0;
    int maxWidth = 0;
    int childState = 0;

    for (int i = 0; i < count; i++) {
        final View child = getChildAt(i);
        if (mMeasureAllChildren || child.getVisibility() != GONE) {
            measureChildWithMargins(child, widthMeasureSpec, 0, heightMeasureSpec, 0);
            final LayoutParams lp = (LayoutParams) child.getLayoutParams();
            maxWidth = Math.max(maxWidth,
                    child.getMeasuredWidth() + lp.leftMargin + lp.rightMargin);
            maxHeight = Math.max(maxHeight,
                    child.getMeasuredHeight() + lp.topMargin + lp.bottomMargin);
            childState = combineMeasuredStates(childState, child.getMeasuredState());
            if (measureMatchParentChildren) {
                if (lp.width == LayoutParams.MATCH_PARENT ||
                        lp.height == LayoutParams.MATCH_PARENT) {
                    mMatchParentChildren.add(child);
                }
            }
        }
    }

    // Account for padding too
    maxWidth += getPaddingLeftWithForeground() + getPaddingRightWithForeground();
    maxHeight += getPaddingTopWithForeground() + getPaddingBottomWithForeground();

    // Check against our minimum height and width
    maxHeight = Math.max(maxHeight, getSuggestedMinimumHeight());
    maxWidth = Math.max(maxWidth, getSuggestedMinimumWidth());

    // Check against our foreground's minimum height and width
    final Drawable drawable = getForeground();
    if (drawable != null) {
        maxHeight = Math.max(maxHeight, drawable.getMinimumHeight());
        maxWidth = Math.max(maxWidth, drawable.getMinimumWidth());
    }

    setMeasuredDimension(resolveSizeAndState(maxWidth, widthMeasureSpec, childState),
            resolveSizeAndState(maxHeight, heightMeasureSpec,
                    childState << MEASURED_HEIGHT_STATE_SHIFT));

    count = mMatchParentChildren.size();
    if (count > 1) {
        for (int i = 0; i < count; i++) {
            final View child = mMatchParentChildren.get(i);
            final MarginLayoutParams lp = (MarginLayoutParams) child.getLayoutParams();

            final int childWidthMeasureSpec;
            if (lp.width == LayoutParams.MATCH_PARENT) {
                final int width = Math.max(0, getMeasuredWidth()
                        - getPaddingLeftWithForeground() - getPaddingRightWithForeground()
                        - lp.leftMargin - lp.rightMargin);
                childWidthMeasureSpec = MeasureSpec.makeMeasureSpec(
                        width, MeasureSpec.EXACTLY);
            } else {
                childWidthMeasureSpec = getChildMeasureSpec(widthMeasureSpec,
                        getPaddingLeftWithForeground() + getPaddingRightWithForeground() +
                        lp.leftMargin + lp.rightMargin,
                        lp.width);
            }

            final int childHeightMeasureSpec;
            if (lp.height == LayoutParams.MATCH_PARENT) {
                final int height = Math.max(0, getMeasuredHeight()
                        - getPaddingTopWithForeground() - getPaddingBottomWithForeground()
                        - lp.topMargin - lp.bottomMargin);
                childHeightMeasureSpec = MeasureSpec.makeMeasureSpec(
                        height, MeasureSpec.EXACTLY);
            } else {
                childHeightMeasureSpec = getChildMeasureSpec(heightMeasureSpec,
                        getPaddingTopWithForeground() + getPaddingBottomWithForeground() +
                        lp.topMargin + lp.bottomMargin,
                        lp.height);
            }

            child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
        }
    }
}

  • 可以看到这里调用了一个循环逻辑，获取该View的所有子View，并执行所有子View的measure方法，这样又回到View的measure方法，这样经过一系列的循环遍历过程，如果是ViewGroup就会调用其ViewGroup的onMeasure方法，若果是View组件就会调用View的onMeasure方法，我们来看一下View的onMeasure方法：

    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    setMeasuredDimension(getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec),
            getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec));
}

  • 可以看到这个方法中调用了setMeasuredDimension方法：

    protected final void setMeasuredDimension(int measuredWidth, int measuredHeight) {
    boolean optical = isLayoutModeOptical(this);
    if (optical != isLayoutModeOptical(mParent)) {
        Insets insets = getOpticalInsets();
        int opticalWidth  = insets.left + insets.right;
        int opticalHeight = insets.top  + insets.bottom;

        measuredWidth  += optical ? opticalWidth  : -opticalWidth;
        measuredHeight += optical ? opticalHeight : -opticalHeight;
    }
    setMeasuredDimensionRaw(measuredWidth, measuredHeight);
}

  • 好吧，方法体里面又调用了setMeasuredDimensionRaw方法：

    private void setMeasuredDimensionRaw(int measuredWidth, int measuredHeight) {
    mMeasuredWidth = measuredWidth;
    mMeasuredHeight = measuredHeight;

    mPrivateFlags |= PFLAG_MEASURED_DIMENSION_SET;
}

  • 这样把View组件即其子View的大小测量出来了，并且保存在了成员变量mMeasuredWith和mMeasuredHeight中。

5.2 performLayout布局

  • 继续回到我们的performTransles方法，然后我们继续看performLayout方法：
    private void performLayout(WindowManager.LayoutParams lp, int desiredWindowWidth,
        int desiredWindowHeight) {
    mLayoutRequested = false;
    mScrollMayChange = true;
    mInLayout = true;

    final View host = mView;
    if (DEBUG_ORIENTATION || DEBUG_LAYOUT) {
        Log.v(TAG, "Laying out " + host + " to (" +
                host.getMeasuredWidth() + ", " + host.getMeasuredHeight() + ")");
    }

    Trace.traceBegin(Trace.TRACE_TAG_VIEW, "layout");
    try {
        host.layout(0, 0, host.getMeasuredWidth(), host.getMeasuredHeight());

        mInLayout = false;
        int numViewsRequestingLayout = mLayoutRequesters.size();
        if (numViewsRequestingLayout > 0) {
            // requestLayout() was called during layout.
            // If no layout-request flags are set on the requesting views, there is no problem.
            // If some requests are still pending, then we need to clear those flags and do
            // a full request/measure/layout pass to handle this situation.
            ArrayList<View> validLayoutRequesters = getValidLayoutRequesters(mLayoutRequesters,
                    false);
            if (validLayoutRequesters != null) {
                // Set this flag to indicate that any further requests are happening during
                // the second pass, which may result in posting those requests to the next
                // frame instead
                mHandlingLayoutInLayoutRequest = true;

                // Process fresh layout requests, then measure and layout
                int numValidRequests = validLayoutRequesters.size();
                for (int i = 0; i < numValidRequests; ++i) {
                    final View view = validLayoutRequesters.get(i);
                    Log.w("View", "requestLayout() improperly called by " + view +
                            " during layout: running second layout pass");
                    view.requestLayout();
                }
                measureHierarchy(host, lp, mView.getContext().getResources(),
                        desiredWindowWidth, desiredWindowHeight);
                mInLayout = true;
                host.layout(0, 0, host.getMeasuredWidth(), host.getMeasuredHeight());

                mHandlingLayoutInLayoutRequest = false;

                // Check the valid requests again, this time without checking/clearing the
                // layout flags, since requests happening during the second pass get noop'd
                validLayoutRequesters = getValidLayoutRequesters(mLayoutRequesters, true);
                if (validLayoutRequesters != null) {
                    final ArrayList<View> finalRequesters = validLayoutRequesters;
                    // Post second-pass requests to the next frame
                    getRunQueue().post(new Runnable() {
                        @Override
                        public void run() {
                            int numValidRequests = finalRequesters.size();
                            for (int i = 0; i < numValidRequests; ++i) {
                                final View view = finalRequesters.get(i);
                                Log.w("View", "requestLayout() improperly called by " + view +
                                        " during second layout pass: posting in next frame");
                                view.requestLayout();
                            }
                        }
                    });
                }
            }

        }
    } finally {
        Trace.traceEnd(Trace.TRACE_TAG_VIEW);
    }
    mInLayout = false;
}
  • 可以看到在方法体中，我们看到该方法执行了layout方法，我们看一下该layout方法的实现：
    public void layout(int l, int t, int r, int b) {
    if ((mPrivateFlags3 & PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT) != 0) {
        onMeasure(mOldWidthMeasureSpec, mOldHeightMeasureSpec);
        mPrivateFlags3 &= ~PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT;
    }

    int oldL = mLeft;
    int oldT = mTop;
    int oldB = mBottom;
    int oldR = mRight;

    boolean changed = isLayoutModeOptical(mParent) ?
            setOpticalFrame(l, t, r, b) : setFrame(l, t, r, b);

    if (changed || (mPrivateFlags & PFLAG_LAYOUT_REQUIRED) == PFLAG_LAYOUT_REQUIRED) {
        onLayout(changed, l, t, r, b);
        mPrivateFlags &= ~PFLAG_LAYOUT_REQUIRED;

        ListenerInfo li = mListenerInfo;
        if (li != null && li.mOnLayoutChangeListeners != null) {
            ArrayList<OnLayoutChangeListener> listenersCopy =
                    (ArrayList<OnLayoutChangeListener>)li.mOnLayoutChangeListeners.clone();
            int numListeners = listenersCopy.size();
            for (int i = 0; i < numListeners; ++i) {
                listenersCopy.get(i).onLayoutChange(this, l, t, r, b, oldL, oldT, oldR, oldB);
            }
        }
    }

    mPrivateFlags &= ~PFLAG_FORCE_LAYOUT;
    mPrivateFlags3 |= PFLAG3_IS_LAID_OUT;
}
  • 可以看到这个方法体中执行了onLayout方法，这个方法就是具体执行测量位置的方法了，由于我们的mDector是一个FrameLayout，所以跟measure类似的，我们看一下FrameLayout的onLayout方法的实现：
    @Override
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
    layoutChildren(left, top, right, bottom, false /* no force left gravity */);
}
    • 可以看到这里调用了layoutChildren方法，让我们来看一下layoutChildren方法的实现：
    void layoutChildren(int left, int top, int right, int bottom,
                              boolean forceLeftGravity) {
    final int count = getChildCount();

    final int parentLeft = getPaddingLeftWithForeground();
    final int parentRight = right - left - getPaddingRightWithForeground();

    final int parentTop = getPaddingTopWithForeground();
    final int parentBottom = bottom - top - getPaddingBottomWithForeground();

    for (int i = 0; i < count; i++) {
        final View child = getChildAt(i);
        if (child.getVisibility() != GONE) {
            final LayoutParams lp = (LayoutParams) child.getLayoutParams();

            final int width = child.getMeasuredWidth();
            final int height = child.getMeasuredHeight();

            int childLeft;
            int childTop;

            int gravity = lp.gravity;
            if (gravity == -1) {
                gravity = DEFAULT_CHILD_GRAVITY;
            }

            final int layoutDirection = getLayoutDirection();
            final int absoluteGravity = Gravity.getAbsoluteGravity(gravity, layoutDirection);
            final int verticalGravity = gravity & Gravity.VERTICAL_GRAVITY_MASK;

            switch (absoluteGravity & Gravity.HORIZONTAL_GRAVITY_MASK) {
                case Gravity.CENTER_HORIZONTAL:
                    childLeft = parentLeft + (parentRight - parentLeft - width) / 2 +
                    lp.leftMargin - lp.rightMargin;
                    break;
                case Gravity.RIGHT:
                    if (!forceLeftGravity) {
                        childLeft = parentRight - width - lp.rightMargin;
                        break;
                    }
                case Gravity.LEFT:
                default:
                    childLeft = parentLeft + lp.leftMargin;
            }

            switch (verticalGravity) {
                case Gravity.TOP:
                    childTop = parentTop + lp.topMargin;
                    break;
                case Gravity.CENTER_VERTICAL:
                    childTop = parentTop + (parentBottom - parentTop - height) / 2 +
                    lp.topMargin - lp.bottomMargin;
                    break;
                case Gravity.BOTTOM:
                    childTop = parentBottom - height - lp.bottomMargin;
                    break;
                default:
                    childTop = parentTop + lp.topMargin;
            }

            child.layout(childLeft, childTop, childLeft + width, childTop + height);
        }
    }
}
  • 跟measure类似的，这里也是遍历执行View的layout方法，若是ViewGroup则执行具体的ViewGroup的layout方法，若是View，则执行View的layout方法，好吧，我们看一下View的layout的具体实现逻辑：
    public void layout(int l, int t, int r, int b) {
    if ((mPrivateFlags3 & PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT) != 0) {
        onMeasure(mOldWidthMeasureSpec, mOldHeightMeasureSpec);
        mPrivateFlags3 &= ~PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT;
    }

    int oldL = mLeft;
    int oldT = mTop;
    int oldB = mBottom;
    int oldR = mRight;

    boolean changed = isLayoutModeOptical(mParent) ?
            setOpticalFrame(l, t, r, b) : setFrame(l, t, r, b);

    if (changed || (mPrivateFlags & PFLAG_LAYOUT_REQUIRED) == PFLAG_LAYOUT_REQUIRED) {
        onLayout(changed, l, t, r, b);
        mPrivateFlags &= ~PFLAG_LAYOUT_REQUIRED;

        ListenerInfo li = mListenerInfo;
        if (li != null && li.mOnLayoutChangeListeners != null) {
            ArrayList<OnLayoutChangeListener> listenersCopy =
                    (ArrayList<OnLayoutChangeListener>)li.mOnLayoutChangeListeners.clone();
            int numListeners = listenersCopy.size();
            for (int i = 0; i < numListeners; ++i) {
                listenersCopy.get(i).onLayoutChange(this, l, t, r, b, oldL, oldT, oldR, oldB);
            }
        }
    }

    mPrivateFlags &= ~PFLAG_FORCE_LAYOUT;
    mPrivateFlags3 |= PFLAG3_IS_LAID_OUT;
}
    • 这样经过layout方法，如果是View组件的话就已经将View组件的位置信息计算出来并保存在对象的成员变量中。

5.3 performDraw绘制

  • 经过了测量大小与测量位置的逻辑之后，最后看一下performTraversals方法中的performDraw方法，这个方法的作用就是执行View组件的绘制逻辑了。
    private void performDraw() {
    draw(fullRedrawNeeded);
}
  • 可以看到这里调用了ViewRootImpl的draw方法，然后我们看一下draw方法的实现：
    private void draw(boolean fullRedrawNeeded) {
    if (!drawSoftware(surface, mAttachInfo, xOffset, yOffset, scalingRequired, dirty)) {
       return;
    }
}
  • 可以看到这里又调用了drawSoftware方法，看名字这里应该就是调用执行绘制的方法：
    private boolean drawSoftware(Surface surface, AttachInfo attachInfo, int xoff, int yoff,
        boolean scalingRequired, Rect dirty) {
    mView.draw(canvas);
    return true;
}
  • 可以看到这里调用了mView的draw方法，这里的mView是我们的mDector，好吧，看一下draw方法的具体实现：
    public void draw(Canvas canvas) {
    final int privateFlags = mPrivateFlags;
    final boolean dirtyOpaque = (privateFlags & PFLAG_DIRTY_MASK) == PFLAG_DIRTY_OPAQUE &&
            (mAttachInfo == null || !mAttachInfo.mIgnoreDirtyState);
    mPrivateFlags = (privateFlags & ~PFLAG_DIRTY_MASK) | PFLAG_DRAWN;

    /*
     * Draw traversal performs several drawing steps which must be executed
     * in the appropriate order:
     *
     *      1. Draw the background
     *      2. If necessary, save the canvas' layers to prepare for fading
     *      3. Draw view's content
     *      4. Draw children
     *      5. If necessary, draw the fading edges and restore layers
     *      6. Draw decorations (scrollbars for instance)
     */

    // Step 1, draw the background, if needed
    int saveCount;

    if (!dirtyOpaque) {
        drawBackground(canvas);
    }

    // skip step 2 & 5 if possible (common case)
    final int viewFlags = mViewFlags;
    boolean horizontalEdges = (viewFlags & FADING_EDGE_HORIZONTAL) != 0;
    boolean verticalEdges = (viewFlags & FADING_EDGE_VERTICAL) != 0;
    if (!verticalEdges && !horizontalEdges) {
        // Step 3, draw the content
        if (!dirtyOpaque) onDraw(canvas);

        // Step 4, draw the children
        dispatchDraw(canvas);

        // Overlay is part of the content and draws beneath Foreground
        if (mOverlay != null && !mOverlay.isEmpty()) {
            mOverlay.getOverlayView().dispatchDraw(canvas);
        }

        // Step 6, draw decorations (foreground, scrollbars)
        onDrawForeground(canvas);

        // we're done...
        return;
    }

    /*
     * Here we do the full fledged routine...
     * (this is an uncommon case where speed matters less,
     * this is why we repeat some of the tests that have been
     * done above)
     */

    boolean drawTop = false;
    boolean drawBottom = false;
    boolean drawLeft = false;
    boolean drawRight = false;

    float topFadeStrength = 0.0f;
    float bottomFadeStrength = 0.0f;
    float leftFadeStrength = 0.0f;
    float rightFadeStrength = 0.0f;

    // Step 2, save the canvas' layers
    int paddingLeft = mPaddingLeft;

    final boolean offsetRequired = isPaddingOffsetRequired();
    if (offsetRequired) {
        paddingLeft += getLeftPaddingOffset();
    }

    int left = mScrollX + paddingLeft;
    int right = left + mRight - mLeft - mPaddingRight - paddingLeft;
    int top = mScrollY + getFadeTop(offsetRequired);
    int bottom = top + getFadeHeight(offsetRequired);

    if (offsetRequired) {
        right += getRightPaddingOffset();
        bottom += getBottomPaddingOffset();
    }

    final ScrollabilityCache scrollabilityCache = mScrollCache;
    final float fadeHeight = scrollabilityCache.fadingEdgeLength;
    int length = (int) fadeHeight;

    // clip the fade length if top and bottom fades overlap
    // overlapping fades produce odd-looking artifacts
    if (verticalEdges && (top + length > bottom - length)) {
        length = (bottom - top) / 2;
    }

    // also clip horizontal fades if necessary
    if (horizontalEdges && (left + length > right - length)) {
        length = (right - left) / 2;
    }

    if (verticalEdges) {
        topFadeStrength = Math.max(0.0f, Math.min(1.0f, getTopFadingEdgeStrength()));
        drawTop = topFadeStrength * fadeHeight > 1.0f;
        bottomFadeStrength = Math.max(0.0f, Math.min(1.0f, getBottomFadingEdgeStrength()));
        drawBottom = bottomFadeStrength * fadeHeight > 1.0f;
    }

    if (horizontalEdges) {
        leftFadeStrength = Math.max(0.0f, Math.min(1.0f, getLeftFadingEdgeStrength()));
        drawLeft = leftFadeStrength * fadeHeight > 1.0f;
        rightFadeStrength = Math.max(0.0f, Math.min(1.0f, getRightFadingEdgeStrength()));
        drawRight = rightFadeStrength * fadeHeight > 1.0f;
    }

    saveCount = canvas.getSaveCount();

    int solidColor = getSolidColor();
    if (solidColor == 0) {
        final int flags = Canvas.HAS_ALPHA_LAYER_SAVE_FLAG;

        if (drawTop) {
            canvas.saveLayer(left, top, right, top + length, null, flags);
        }

        if (drawBottom) {
            canvas.saveLayer(left, bottom - length, right, bottom, null, flags);
        }

        if (drawLeft) {
            canvas.saveLayer(left, top, left + length, bottom, null, flags);
        }

        if (drawRight) {
            canvas.saveLayer(right - length, top, right, bottom, null, flags);
        }
    } else {
        scrollabilityCache.setFadeColor(solidColor);
    }

    // Step 3, draw the content
    if (!dirtyOpaque) onDraw(canvas);

    // Step 4, draw the children
    dispatchDraw(canvas);

    // Step 5, draw the fade effect and restore layers
    final Paint p = scrollabilityCache.paint;
    final Matrix matrix = scrollabilityCache.matrix;
    final Shader fade = scrollabilityCache.shader;

    if (drawTop) {
        matrix.setScale(1, fadeHeight * topFadeStrength);
        matrix.postTranslate(left, top);
        fade.setLocalMatrix(matrix);
        p.setShader(fade);
        canvas.drawRect(left, top, right, top + length, p);
    }

    if (drawBottom) {
        matrix.setScale(1, fadeHeight * bottomFadeStrength);
        matrix.postRotate(180);
        matrix.postTranslate(left, bottom);
        fade.setLocalMatrix(matrix);
        p.setShader(fade);
        canvas.drawRect(left, bottom - length, right, bottom, p);
    }

    if (drawLeft) {
        matrix.setScale(1, fadeHeight * leftFadeStrength);
        matrix.postRotate(-90);
        matrix.postTranslate(left, top);
        fade.setLocalMatrix(matrix);
        p.setShader(fade);
        canvas.drawRect(left, top, left + length, bottom, p);
    }

    if (drawRight) {
        matrix.setScale(1, fadeHeight * rightFadeStrength);
        matrix.postRotate(90);
        matrix.postTranslate(right, top);
        fade.setLocalMatrix(matrix);
        p.setShader(fade);
        canvas.drawRect(right - length, top, right, bottom, p);
    }

    canvas.restoreToCount(saveCount);

    // Overlay is part of the content and draws beneath Foreground
    if (mOverlay != null && !mOverlay.isEmpty()) {
        mOverlay.getOverlayView().dispatchDraw(canvas);
    }

    // Step 6, draw decorations (foreground, scrollbars)
    onDrawForeground(canvas);
}
  • 整个View的绘制流程还是比较清楚的，整个执行逻辑还有相应的注释，并且在执行draw方法的过程中，如果包含子View，那么也会执行子View的draw方法，好吧，经过这样一系列的执行逻辑之后，mDector以及子View就被绘制出来了。

06.Activity布局绘制总结

  • 总结如下所示：
    • Activity执行onResume之后再ActivityThread中执行Activity的makeVisible方法。
    • View的绘制流程包含了测量大小，测量位置，绘制三个流程；
    • Activity的界面绘制是从mDoctor即根View开始的，也就是从mDoctor的测量大小，测量位置，绘制三个流程；
    • View体系的绘制流程是从ViewRootImpl的performTraversals方法开始的；
    • View的测量大小流程:performMeasure --> measure --> onMeasure等方法;
    • View的测量位置流程：performLayout --> layout --> onLayout等方法；
    • View的绘制流程：onDraw等方法；
    • View组件的绘制流程会在onMeasure,onLayout以及onDraw方法中执行分发逻辑，也就是在onMeasure同时执行子View的测量大小逻辑，在onLayout中同时执行子View的测量位置逻辑，在onDraw中同时执行子View的绘制逻辑；
    • Activity中都对应这个一个Window对象，而每一个Window对象都对应着一个新的WindowManager对象（WindowManagerImpl实例）；

07.Activity布局绘制流程图

  • 如图所示
    • img
      img
  • View的绘制是从上往下一层层迭代下来的。DecorView-->ViewGroup（--->ViewGroup）-->View ，按照这个流程从上往下，依次measure(测量),layout(布局),draw(绘制)。
    • img
      img

其他介绍

01.关于博客汇总链接

02.关于我的博客

  • github：https://github.com/yangchong211
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