Android中View绘制过程（一） decorView绘制

雨点打透心脏的1/2处 2022-06-14 08:22 223阅读 0赞

第一次

Activity的显示是在onResume()之后这一点大家都知道，代码在ActivityThread中，还是不去管Activity的启动过程，只去看一下在没有setContentView的时候decorView这里是怎么添加的并且第一调用performTraversals()的。

在ActivityThread.java中，代码

handleResumeActivity()函数中调用wm.addView(decor, l);将decorView添加。

在WindowManagerImpl代码如下

@Override
        public void addView(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
            applyDefaultToken(params);
            mGlobal.addView(view, params, mContext.getDisplay(), mParentWindow);
        }

在WindowManagerGlobal代码太多不粘贴了有这样的调用

view.setLayoutParams(wparams);

点进入之后

public void setLayoutParams(ViewGroup.LayoutParams params) {
            if (params == null) {
                throw new NullPointerException("Layout parameters cannot be null");
            }
            mLayoutParams = params;
            resolveLayoutParams();
            if (mParent instanceof ViewGroup) {
                ((ViewGroup) mParent).onSetLayoutParams(this, params);
            }
            requestLayout();
        }

最后这句requestLayout(),这应该是第一回的调用吧。点进去

if (mParent != null && !mParent.isLayoutRequested()) {
                mParent.requestLayout();
            }

这里mParent就是ViewRootImp看一下这个调用

@Override
        public void requestLayout() {
            if (!mHandlingLayoutInLayoutRequest) {
                checkThread();
                mLayoutRequested = true;
                scheduleTraversals();
            }
        }

调用如下代码

void scheduleTraversals() {
            if (!mTraversalScheduled) {
                mTraversalScheduled = true;
                mTraversalBarrier = mHandler.getLooper().getQueue().postSyncBarrier();
                mChoreographer.postCallback(
                        Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null);
                if (!mUnbufferedInputDispatch) {
                    scheduleConsumeBatchedInput();
                }
                notifyRendererOfFramePending();
                pokeDrawLockIfNeeded();
            }
        }

post这个Runnable

final class TraversalRunnable implements Runnable {
            @Override
            public void run() {
                doTraversal();
            }
        }

继续调用就到了熟悉的代码了，performTraversals()。

void doTraversal() {
            if (mTraversalScheduled) {
                mTraversalScheduled = false;
                mHandler.getLooper().getQueue().removeSyncBarrier(mTraversalBarrier);
    
                if (mProfile) {
                    Debug.startMethodTracing("ViewAncestor");
                }
    
                performTraversals();
    
                if (mProfile) {
                    Debug.stopMethodTracing();
                    mProfile = false;
                }
            }
        }

第二次

WindowManagerGlobal中接下来调用ViewRootImpl 的setView

root.setView(view, wparams, panelParentView);

// Schedule the first layout -before- adding to the window
                    // manager, to make sure we do the relayout before receiving
                    // any other events from the system.
                    requestLayout();

这里注释写到，是第一次的layout，在Window还没有添加之前的调用。然后才添加Window到界面上

res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,
                                getHostVisibility(), mDisplay.getDisplayId(),
                                mAttachInfo.mContentInsets, mAttachInfo.mStableInsets,
                                mAttachInfo.mOutsets, mInputChannel);