View加载和绘制

[TOC]

Activity的相关生命周期

ActivityThread中:

private Activity performLaunchActivity(){
    ...
    ContextImpl appContext = createBaseContextForActivity(r);
    java.lang.ClassLoader cl = appContext.getClassLoader();
    //创建activity对象
    Activity activity = null;
    activity = mInstrumentation.newActivity(cl, component.getClassName(), r.intent);

    Window window = null;
    if (r.mPendingRemoveWindow != null && r.mPreserveWindow) {
        window = r.mPendingRemoveWindow;
    }
    
    //调用Activity的attach()
    activity.attach(...,window,...)
    
    //调用Activity的onPerfermCreate()->onCreate()
    mInstrumentation.callActivityOnCreate(activity, r.state);
}

• r是ActivityClientRecord对象，每个activity启动前会创建一个，用于保存：
  • Binder对象
  • Intent对象
  • Bundle对象
  • Window对象
  • ActiityInfo对象，他包含theme，launcherMode，permission，taskAffinity，flags等
  • Activity对象本身和上级Activity对象
  • 各种Configuration
  • 生命周期状态等

Activity的attach()中：

final void attach(...){
    mWindow = new PhoneWindow(this, window, activityConfigCallback);
    ...
    //mToken是当前Activity的IBinder对象，传递给WMS进程
    mWindow.setWindowManager((WindowManager)context.getSystemService(Context.WINDOW_SERVICE),mToken,...);
    if (mParent != null) {
        mWindow.setContainer(mParent.getWindow());
    }    
    mWindowManager = mWindow.getWindowManager();
}

View加载

ActivityThread中：

public void handleResumeActivity(...){
    final ActivityClientRecord r = mActivities.get(token);
    final Activity a = r.activity;
    
    if (r.window == null && !a.mFinished && willBeVisible) {
        //获取PhoneWindow对象
        r.window = r.activity.getWindow();
        //r.window是Window的实现类phoneWindow对象，实现方法getDecorView()中创建了DecorView
        //获取DecorView对象
        View decor = r.window.getDecorView();
        decor.setVisibility(View.INVISIBLE);
        //前面Activity的attach()中初始化了WindowManager
        //这里获取了WindowManagerImpl的对象
        ViewManager wm = a.getWindowManager();
        WindowManager.LayoutParams l = r.window.getAttributes();
        a.mDecor = decor;
        wm.addView(decor, l);
    }        
}

• WindowManager是个接口，管理window对象，这里调用了实现类WindowManagerImpl的addView(),通过桥接模式又调用了WindowManagerGlobal的addView()
• WindowManagerGlobal是单例，保存了所有Window对象和ViewRootImol对象和LayoutParams对象,通过对比activity的token(Binder)和这3个对象的token判断是哪个activity的

public void addView(View view, ViewGroup.LayoutParams params,...){
    ViewRootImpl root = new ViewRootImpl(view.getContext(), display);
    view.setLayoutParams(wparams);
    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.setView(view, wparams, panelParentView);
}

• ViewRootImpl管理view，surface，与WMS通信

ViewRootImpl的setView()

    public void setView(View view,...){
        ...
        requestLayout();
        //IWindowSession是远程接口代理，WMS的Binder对象,这里是通知WMS渲染
        res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,
                            getHostVisibility(), mDisplay.getDisplayId(), mTmpFrame,
                            mAttachInfo.mContentInsets, mAttachInfo.mStableInsets,
                            mAttachInfo.mOutsets, mAttachInfo.mDisplayCutout, mInputChannel,
                            mTempInsets);
        setFrame(mTmpFrame);
    }

    public void requestLayout() {
        if (!mHandlingLayoutInLayoutRequest) {
            //这里会检查是否主线程
            checkThread();
            mLayoutRequested = true;
            scheduleTraversals();
        }
    }
    //间接调用到
    private void performTraversals(){
        //生成测量规则，这是一个32位2进制数，前2位表示测量模式，后30位表示大小
        int childWidthMeasureSpec = getRootMeasureSpec(mWidth, lp.width);
        int childHeightMeasureSpec = getRootMeasureSpec(mHeight, lp.height);
        
        performMeasure(childWidthMeasureSpec, childHeightMeasureSpec);
        //调用到View的measure方法,这里是DecorView对象,所以调用到FrameLayout的onMeasure()
        //mView.measure(childWidthMeasureSpec, childHeightMeasureSpec);
        
        performLayout(lp, mWidth, mHeight);
        //mView.layout(0, 0, host.getMeasuredWidth(), host.getMeasuredHeight());
        performDraw();
    }

Framelayout中:

onMeasure

protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    int count = getChildCount();
    for (int i = 0; i < count; i++) {
            final View child = getChildAt(i);
            if (mMeasureAllChildren || child.getVisibility() != GONE) {
                //这里传入子view和父容器的测量规则，调用子view的测量方法
                //child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
                measureChildWithMargins(child, widthMeasureSpec, 0, heightMeasureSpec, 0);
                final LayoutParams lp = (LayoutParams) child.getLayoutParams();
                //FrameLayout的宽高是child中最宽或最高的那个
                maxWidth = Math.max(maxWidth,child.getMeasuredWidth() + lp.leftMargin + lp.rightMargin);
                maxHeight = Math.max(maxHeight,child.getMeasuredHeight() + lp.topMargin + lp.bottomMargin);
            }
    }
    setMeasuredDimension(resolveSizeAndState(maxWidth, widthMeasureSpec, childState),resolveSizeAndState(maxHeight, heightMeasureSpec,childState << MEASURED_HEIGHT_STATE_SHIFT));
    
    //如果Framelayout不是精确模式,即宽高是Wrap，宽或高为Match的child会受他的最终大小影响，所以在此调用这些child的再次测量
    for (int i = 0; i < count; i++) {
        final View child = mMatchParentChildren.get(i);
        ...
        child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
    }
}

onLayout

protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
    layoutChildren(left, top, right, bottom, false);
}

void layoutChildren(int left, int top, int right, int bottom, boolean forceLeftGravity) {
    final int count = getChildCount();
    for (int i = 0; i < count; i++) {
        final View child = getChildAt(i);
        ...
        child.layout(childLeft, childTop, childLeft + width, childTop + height);
    }    
}

onDraw

ViewRootImpl的performDraw()会调用到

public final Surface mSurface = new Surface();

private boolean drawSoftware(Surface surface,Rect dirty,...){
    final Canvas canvas;
    //view绘制用的画布，是在Surface对象上截取的一个rect范围
    //mDirty.set(0, 0, mWidth, mHeight);DecorView的范围是Window的宽高
    canvas = mSurface.lockCanvas(dirty);
    canvas.setDensity(mDensity);
    //这里会调用onDraw(),容器是空实现，非容器View绘制视图
    mView.draw(canvas);
}

draw方法6步：

    *      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)

关键环节

• Activity创建后调用的attach方法中，初始化了PhoneWindow对象，WindowManager对象
• WindowManager初始化时，赋值的是WindowManagerImpl对象
• PhoneWindow实现了Window的getDecorView方法，这里创建了DecorView对象
• handleResumeActivity()中获取了decorView对象和wm的params，由wm开始addView，wm是window的管理器，addview中创建了ViewRootImpl对象，这是view树的根和管理器
• ViewRootImpl的setView被wm触发后，调用requestLayout，这里开始view三步骤

关于测量2次

performTranversal被执行2次

关于测量模式

• EXACTLY：表示设置了精确的值，一般当View或childView设置其宽、高为精确值、match_parent时，会将其设置为EXACTLY
• AT_MOST：表示子布局被限制在一个最大值内，一般当View或childView设置其宽高为wrap_content时，会将其设置为AT_MOST
• UNSPECIFIED：表示子布局想多大多大，一般出现在AadapterView的item的heightMode中、ScrollView的childView的heightMode中