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各位看官们,大家好,上一回中咱们说的是Android中View内部流程的例子,这一回咱们继续说该例子。闲话休提,言归正转。让我们一起Talk Android吧!
看官们,我们在上一章回中介绍了Viwe内部流程中的规划,这一回是我们介绍它的第三个内部流程:绘制(draw)。
绘制主要是对各个组件进行绘制,只有在组件被绘制完成后才能被我们看到。绘制功能主要是通过performDraw()
函数实现的,下面是它的源代码:
private void performDraw() {
if (mAttachInfo.mDisplayState == Display.STATE_OFF && !mReportNextDraw) {
return;
} else if (mView == null) {
return;
}
final boolean fullRedrawNeeded = mFullRedrawNeeded || mReportNextDraw;
mFullRedrawNeeded = false;
mIsDrawing = true;
Trace.traceBegin(Trace.TRACE_TAG_VIEW, "draw");
boolean usingAsyncReport = false;
if (mReportNextDraw && mAttachInfo.mThreadedRenderer != null
&& mAttachInfo.mThreadedRenderer.isEnabled()) {
usingAsyncReport = true;
mAttachInfo.mThreadedRenderer.setFrameCompleteCallback((long frameNr) -> {
// TODO: Use the frame number
pendingDrawFinished();
});
}
try {
boolean canUseAsync = draw(fullRedrawNeeded);
if (usingAsyncReport && !canUseAsync) {
mAttachInfo.mThreadedRenderer.setFrameCompleteCallback(null);
usingAsyncReport = false;
}
} finally {
mIsDrawing = false;
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
}
// For whatever reason we didn't create a HardwareRenderer, end any
// hardware animations that are now dangling
if (mAttachInfo.mPendingAnimatingRenderNodes != null) {
final int count = mAttachInfo.mPendingAnimatingRenderNodes.size();
for (int i = 0; i < count; i++) {
mAttachInfo.mPendingAnimatingRenderNodes.get(i).endAllAnimators();
}
mAttachInfo.mPendingAnimatingRenderNodes.clear();
}
if (mReportNextDraw) {
mReportNextDraw = false;
// if we're using multi-thread renderer, wait for the window frame draws
if (mWindowDrawCountDown != null) {
try {
mWindowDrawCountDown.await();
} catch (InterruptedException e) {
Log.e(mTag, "Window redraw count down interrupted!");
}
mWindowDrawCountDown = null;
}
if (mAttachInfo.mThreadedRenderer != null) {
mAttachInfo.mThreadedRenderer.setStopped(mStopped);
}
if (LOCAL_LOGV) {
Log.v(mTag, "FINISHED DRAWING: " + mWindowAttributes.getTitle());
}
if (mSurfaceHolder != null && mSurface.isValid()) {
SurfaceCallbackHelper sch = new SurfaceCallbackHelper(this::postDrawFinished);
SurfaceHolder.Callback callbacks[] = mSurfaceHolder.getCallbacks();
sch.dispatchSurfaceRedrawNeededAsync(mSurfaceHolder, callbacks);
} else if (!usingAsyncReport) {
if (mAttachInfo.mThreadedRenderer != null) {
mAttachInfo.mThreadedRenderer.fence();
}
pendingDrawFinished();
}
}
}
大家可以看到其核心功能是通过draw()
函数实现的,下一章回中我们将详细介绍它。
各位看官,关于Androd中View的内部流程的例子咱们就介绍到这里,欲知后面还有什么例子,且听下回分解!