博客首页:http://www.cnblogs.com/kezhuang/p/
View绘制的三部曲,测量,布局,绘画
现在我们分析绘画部分
测量和布局 在前两篇文章中已经分析过了。不了解的可以去我的博客里找一下
下面进入正题,开始分析调用以及函数原理
private void performDraw() {
if (mAttachInfo.mDisplayState == Display.STATE_OFF && !mReportNextDraw) {
return;
}
final boolean fullRedrawNeeded = mFullRedrawNeeded;
mFullRedrawNeeded = false;
mIsDrawing = true;
Trace.traceBegin(Trace.TRACE_TAG_VIEW, "draw");
try {
//调用内部实现方法,来实现分发绘画的工作
draw(fullRedrawNeeded);
} finally {
mIsDrawing = false;
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
}
//...
}
这个函数调用内部draw方法去处理绘画前的工作,来继续完成绘制工作
private void draw(boolean fullRedrawNeeded) {
Surface surface = mSurface;
if (!surface.isValid()) {
return;
}
if (DEBUG_FPS) {
trackFPS();
}
//出发绘制监听
if (!sFirstDrawComplete) {
synchronized (sFirstDrawHandlers) {
sFirstDrawComplete = true;
final int count = sFirstDrawHandlers.size();
for (int i = 0; i< count; i++) {
mHandler.post(sFirstDrawHandlers.get(i));
}
}
}
//当界面需要滚动的时候,这个方法会触发Scroller类下的startScroll函数
scrollToRectOrFocus(null, false);
//如果界面发生了滚动,就分发滚动监听
if (mAttachInfo.mViewScrollChanged) {
mAttachInfo.mViewScrollChanged = false;
mAttachInfo.mTreeObserver.dispatchOnScrollChanged();
}
boolean animating = mScroller != null && mScroller.computeScrollOffset();
final int curScrollY;
if (animating) {
curScrollY = mScroller.getCurrY();
} else {
curScrollY = mScrollY;
}
if (mCurScrollY != curScrollY) {
mCurScrollY = curScrollY;
fullRedrawNeeded = true;
if (mView instanceof RootViewSurfaceTaker) {
((RootViewSurfaceTaker) mView).onRootViewScrollYChanged(mCurScrollY);
}
}
final float appScale = mAttachInfo.mApplicationScale;
final boolean scalingRequired = mAttachInfo.mScalingRequired;
int resizeAlpha = 0;
if (mResizeBuffer != null) {
long deltaTime = SystemClock.uptimeMillis() - mResizeBufferStartTime;
if (deltaTime < mResizeBufferDuration) {
float amt = deltaTime/(float) mResizeBufferDuration;
amt = mResizeInterpolator.getInterpolation(amt);
animating = true;
resizeAlpha = 255 - (int)(amt*255);
} else {
disposeResizeBuffer();
}
}
final Rect dirty = mDirty;
if (mSurfaceHolder != null) {
// The app owns the surface, we won't draw.
dirty.setEmpty();
if (animating) {
if (mScroller != null) {
mScroller.abortAnimation();
}
disposeResizeBuffer();
}
return;
}
if (fullRedrawNeeded) {
mAttachInfo.mIgnoreDirtyState = true;
dirty.set(0, 0, (int) (mWidth * appScale + 0.5f), (int) (mHeight * appScale + 0.5f));
}
if (DEBUG_ORIENTATION || DEBUG_DRAW) {
Log.v(TAG, "Draw " + mView + "/"
+ mWindowAttributes.getTitle()
+ ": dirty={" + dirty.left + "," + dirty.top
+ "," + dirty.right + "," + dirty.bottom + "} surface="
+ surface + " surface.isValid()=" + surface.isValid() + ", appScale:" +
appScale + ", width=" + mWidth + ", height=" + mHeight);
}
//如果有注册TreeObserver下的监听,在调用onDraw之前会触发
mAttachInfo.mTreeObserver.dispatchOnDraw();
int xOffset = 0;
int yOffset = curScrollY;
final WindowManager.LayoutParams params = mWindowAttributes;
final Rect surfaceInsets = params != null ? params.surfaceInsets : null;
if (surfaceInsets != null) {
xOffset -= surfaceInsets.left;
yOffset -= surfaceInsets.top;
// Offse