invalidate和postInvalidate的区别及使用

总结：

invalidate在主线程中调用，postInvalidate在子线程中调用，最终调的也是view.invalidate()

invalidate() -> parent.invalidateChild() -> 层层找到parent，parent.invalidateChildInParent()，直到ViewRootImpl

ViewRootImpl.invalidateChildInParent() -> invalidateRectOnScreen() -> scheduleTraversals() -> doTraversal() -> performTraversals() -> 根据条件去执行performMeasure() / performLayout / performDraw

也就是说任意一个子View调用invalidate，最终都会到ViewRootImpl的performTraversals

View树级结构：ViewRootImpl -> DecorView -> contentView -> R.layout.xxx.xml

View#invalidate()

public void invalidate() { invalidate(true); }

postInvalidate()

通过ViewRootImpl中的ViewRootHandler进行线程调度，切到主线程，同样的调用view.invalidate()attachInfo是在new ViewRootImpl(context, display)中创建的attachInfo是在performTraversals()，通过host(decorView)层层遍历，传给每一个ViewGroup/View

View#postInvalidate()

public void postInvalidate() { postInvalidateDelayed(0); } public void postInvalidateDelayed(long delayMilliseconds) { final AttachInfo attachInfo = mAttachInfo; if (attachInfo != null) { attachInfo.mViewRootImpl.dispatchInvalidateDelayed(this, delayMilliseconds); } }

ViewRootImpl#dispatchInvalidateDelayed(view, delayMilliseconds)

public void dispatchInvalidateDelayed(View view, long delayMilliseconds) { Message msg = mHandler.obtainMessage(MSG_INVALIDATE, view); mHandler.sendMessageDelayed(msg, delayMilliseconds); } final ViewRootHandler mHandler = new ViewRootHandler(); final class ViewRootHandler extends Handler { @Override public void handleMessage(Message msg) { switch (msg.what) { case MSG_INVALIDATE: ((View) msg.obj).invalidate(); break; } }