自定义View——invalidate传递与绘制流程分析
AdrianaMcca
8年前
<p>上一篇文章 <a href="http://www.open-open.com/lib/view/open1470726951907.html" rel="nofollow,noindex">自定义View——View的弹性滑动</a> 中，我们对View的滑动进行了实战以及简单分析。但在文章的最后，仍然遗留了两个问题,第一个是invalidate与postInvalidate有什么区别呢？第二个是invalidate是如何调用computeScroll()方法的呢？这两个问题将在这一篇文章中进行分析。</p> <h2>一、invalidate与postInvalidate</h2> <p>invalidate与postInvadlidate都是用于请求View重绘的API，invalidate在主线程中进行调用，而postInvadlidate则在子线程中进行调用。</p> <p>我们来分析下postInvadlidate的源码 :</p> <pre> <code class="language-java">public void postInvalidate() { postInvalidateDelayed(0); }</code></pre> <p>postInvalidate()蒋会调用postInvalidateDelayed(0)方法，继续跟进。</p> <pre> <code class="language-java">public void postInvalidateDelayed(long delayMilliseconds) { final AttachInfo attachInfo = mAttachInfo; if (attachInfo != null) { attachInfo.mViewRootImpl.dispatchInvalidateDelayed(this, delayMilliseconds); } }</code></pre> <p>postInvalidateDelayed方法，通过attachInfo获取到当前的ViewRootImpl对象，调用它的dispatchInvalidateDelayed方法</p> <pre> <code class="language-java">public void dispatchInvalidateDelayed(View view, long delayMilliseconds) { Message msg = mHandler.obtainMessage(MSG_INVALIDATE, view); mHandler.sendMessageDelayed(msg, delayMilliseconds); }</code></pre> <p>从上面的源码已经可以看出，postInvalidate的子线程这一个特性了。再继续跟下去看看。</p> <pre> <code class="language-java">@Override public void handleMessage(Message msg) { switch (msg.what) { case MSG_INVALIDATE: ((View) msg.obj).invalidate(); break; ... } }</code></pre> <p>代码跟到这里，也就明白了，postInvalidate通过sendMessageDelayed的方法，加入到了looper中，之后在handleMessage中再调用对应View的invalidate()方法，请求View重绘。</p> <h2>二、invalidate流程分析</h2> <p>现在我们来看看invalidate是如何让View进行重绘的呢？</p> <p>(PS:我这里使用的API版本为23，具体的代码可能和其他的版本有稍许不同)</p> <h3>1、invalidate的请求传递</h3> <p>我们的旅程从View的invalidate传递过程开始</p> <p>现在来看看View#invalidate()方法。</p> <pre> <code class="language-java">public void invalidate() { invalidate(true); } void invalidate(boolean invalidateCache) { invalidateInternal(0, 0, mRight - mLeft, mBottom - mTop, invalidateCache, true); }</code></pre> <p>invalidate调用View#invalidateInternal方法传入当前View的位置参数。</p> <pre> <code class="language-java">void invalidateInternal(int l, int t, int r, int b, boolean invalidateCache, boolean fullInvalidate) { // 如果View重绘，则它也将重绘 if (mGhostView != null) { mGhostView.invalidate(true); return; } // View是否可见，是否在动画运行中 if (skipInvalidate()) { return; } // 根据View的标记来判断View是否需要进行重绘 if ((mPrivateFlags & (PFLAG_DRAWN | PFLAG_HAS_BOUNDS)) == (PFLAG_DRAWN | PFLAG_HAS_BOUNDS) || (invalidateCache && (mPrivateFlags & PFLAG_DRAWING_CACHE_VALID) == PFLAG_DRAWING_CACHE_VALID) || (mPrivateFlags & PFLAG_INVALIDATED) != PFLAG_INVALIDATED || (fullInvalidate && isOpaque() != mLastIsOpaque)) { if (fullInvalidate) { mLastIsOpaque = isOpaque(); mPrivateFlags &= ~PFLAG_DRAWN; } // 设置标志，表明View正在被重绘 mPrivateFlags |= PFLAG_DIRTY; //清除缓存，设置标志，表明重绘由当前View发起 if (invalidateCache) { mPrivateFlags |= PFLAG_INVALIDATED; mPrivateFlags &= ~PFLAG_DRAWING_CACHE_VALID; } // 把需要重绘的View区域传递给父View final AttachInfo ai = mAttachInfo; final ViewParent p = mParent; if (p != null && ai != null && l < r && t < b) { final Rect damage = ai.mTmpInvalRect; // 设置重绘区域 damage.set(l, t, r, b); // 关键代码，调用父View的方法，向上传递重绘事件 p.invalidateChild(this, damage); } ... } }</code></pre> <p>上述代码中，会判断当前View的状态，是否需要进行重绘，之后设置一系列标记位。通过父View的invalidateChild(this, damage)方法，将需要重绘的区域传递给父View。</p> <p>接着来看下ViewGroup#invalidateChild方法，这里仅截取了其中的主要代码</p> <pre> <code class="language-java">public final void invalidateChild(View child, final Rect dirty) { ViewParent parent = this; final AttachInfo attachInfo = mAttachInfo; if (attachInfo != null) { ... // 保存子View的left、top final int[] location = attachInfo.mInvalidateChildLocation; location[CHILD_LEFT_INDEX] = child.mLeft; location[CHILD_TOP_INDEX] = child.mTop; if (!childMatrix.isIdentity() || (mGroupFlags & ViewGroup.FLAG_SUPPORT_STATIC_TRANSFORMATIONS) != 0) { RectF boundingRect = attachInfo.mTmpTransformRect; boundingRect.set(dirty); Matrix transformMatrix; if ((mGroupFlags & ViewGroup.FLAG_SUPPORT_STATIC_TRANSFORMATIONS) != 0) { Transformation t = attachInfo.mTmpTransformation; boolean transformed = getChildStaticTransformation(child, t); if (transformed) { transformMatrix = attachInfo.mTmpMatrix; transformMatrix.set(t.getMatrix()); if (!childMatrix.isIdentity()) { transformMatrix.preConcat(childMatrix); } } else { transformMatrix = childMatrix; } } else { transformMatrix = childMatrix; } transformMatrix.mapRect(boundingRect); // 设置需要重绘的区域 dirty.set((int) (boundingRect.left - 0.5f), (int) (boundingRect.top - 0.5f), (int) (boundingRect.right + 0.5f), (int) (boundingRect.bottom + 0.5f)); } // 这里的do...while方法，让view可以不断的去调用父类的 // invalidateChildInParent方法，来传递重绘请求 do { View view = null; if (parent instanceof View) { view = (View) parent; } if (drawAnimation) { if (view != null) { view.mPrivateFlags |= PFLAG_DRAW_ANIMATION; } else if (parent instanceof ViewRootImpl) { ((ViewRootImpl) parent).mIsAnimating = true; } } // If the parent is dirty opaque or not dirty, mark it dirty with the opaque // flag coming from the child that initiated the invalidate if (view != null) { if ((view.mViewFlags & FADING_EDGE_MASK) != 0 && view.getSolidColor() == 0) { opaqueFlag = PFLAG_DIRTY; } if ((view.mPrivateFlags & PFLAG_DIRTY_MASK) != PFLAG_DIRTY) { view.mPrivateFlags = (view.mPrivateFlags & ~PFLAG_DIRTY_MASK) | opaqueFlag; } } // 这里是关键代码，他会调用父类的 parent = parent.invalidateChildInParent(location, dirty); if (view != null) { // Account for transform on current parent Matrix m = view.getMatrix(); if (!m.isIdentity()) { RectF boundingRect = attachInfo.mTmpTransformRect; boundingRect.set(dirty); m.mapRect(boundingRect); dirty.set((int) (boundingRect.left - 0.5f), (int) (boundingRect.top - 0.5f), (int) (boundingRect.right + 0.5f), (int) (boundingRect.bottom + 0.5f)); } } } while (parent != null); } }</code></pre> <p>上述代码中，设置了需要重绘的区域dirty。之后再do…while方法中，反复的调用 parent = parent.invalidateChildInParent(location, dirty) 方法，来调用父类的invalidateChildInParent对View的重绘请求进行传递。这里的parent有可能是ViewGroup，也有可能是ViewRoot，我们先来看看ViewGroup#invalidateChildInParent方法</p> <pre> <code class="language-java">public ViewParent invalidateChildInParent(final int[] location, final Rect dirty) { if ((mPrivateFlags & PFLAG_DRAWN) == PFLAG_DRAWN || (mPrivateFlags & PFLAG_DRAWING_CACHE_VALID) == PFLAG_DRAWING_CACHE_VALID) { if ((mGroupFlags & (FLAG_OPTIMIZE_INVALIDATE | FLAG_ANIMATION_DONE)) != FLAG_OPTIMIZE_INVALIDATE) { // 子View中的布局位置转换为父View中的布局位置 dirty.offset(location[CHILD_LEFT_INDEX] - mScrollX, location[CHILD_TOP_INDEX] - mScrollY); if ((mGroupFlags & FLAG_CLIP_CHILDREN) == 0) { // 合并绘制区域集合 dirty.union(0, 0, mRight - mLeft, mBottom - mTop); } final int left = mLeft; final int top = mTop; if ((mGroupFlags & FLAG_CLIP_CHILDREN) == FLAG_CLIP_CHILDREN) { if (!dirty.intersect(0, 0, mRight - left, mBottom - top)) { dirty.setEmpty(); } } mPrivateFlags &= ~PFLAG_DRAWING_CACHE_VALID; location[CHILD_LEFT_INDEX] = left; location[CHILD_TOP_INDEX] = top; if (mLayerType != LAYER_TYPE_NONE) { mPrivateFlags |= PFLAG_INVALIDATED; } return mParent; } else { mPrivateFlags &= ~PFLAG_DRAWN & ~PFLAG_DRAWING_CACHE_VALID; location[CHILD_LEFT_INDEX] = mLeft; location[CHILD_TOP_INDEX] = mTop; if ((mGroupFlags & FLAG_CLIP_CHILDREN) == FLAG_CLIP_CHILDREN) { dirty.set(0, 0, mRight - mLeft, mBottom - mTop); } else { // in case the dirty rect extends outside the bounds of this container dirty.union(0, 0, mRight - mLeft, mBottom - mTop); } if (mLayerType != LAYER_TYPE_NONE) { mPrivateFlags |= PFLAG_INVALIDATED; } return mParent; } } return null; }</code></pre> <p>在上述代码中，将会使用offset，把子View需要重绘的坐标区域转换为父View中的坐标区域。之后使用union对子View与父View的区域进行集合运算，获得需要绘制的区域。</p> <p>接下来我们再来看看ViewRoot#invalidateChildInParent方法，ViewRoot并不是View，ViewRoot的实现类为ViewRootImpl，我们来看下它的invalidateChildInParent方法。</p> <pre> <code class="language-java">@Override public ViewParent invalidateChildInParent(int[] location, Rect dirty) { // 检查线程是否为创建View的线程，即创建View的线程中是否含有此ViewRootImpl checkThread(); if (DEBUG_DRAW) Log.v(TAG, "Invalidate child: " + dirty); // 检查重绘区域 if (dirty == null) { invalidate(); return null; } else if (dirty.isEmpty() && !mIsAnimating) { return null; } // 动画和滑动的检查设置 if (mCurScrollY != 0 || mTranslator != null) { mTempRect.set(dirty); dirty = mTempRect; if (mCurScrollY != 0) { dirty.offset(0, -mCurScrollY); } if (mTranslator != null) { mTranslator.translateRectInAppWindowToScreen(dirty); } if (mAttachInfo.mScalingRequired) { dirty.inset(-1, -1); } } invalidateRectOnScreen(dirty); return null; } private void invalidateRectOnScreen(Rect dirty) { ... if (!mWillDrawSoon && (intersected || mIsAnimating)) { //关键代码，ViewTree列表 scheduleTraversals(); } }</code></pre> <p>上述代码中，进入之后会线程以及重绘区域的检查，之后调用invalidateRectOnScreen方法，然后调用scheduleTraversals()方法。</p> <p>来继续看看ViewRootImpl#scheduleTraversals()。</p> <pre> <code class="language-java">void scheduleTraversals() { if (!mTraversalScheduled) { mTraversalScheduled = true; // handler消息传递绘制请求 mTraversalBarrier = mHandler.getLooper().getQueue().postSyncBarrier(); mChoreographer.postCallback( Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null); if (!mUnbufferedInputDispatch) { scheduleConsumeBatchedInput(); } notifyRendererOfFramePending(); pokeDrawLockIfNeeded(); } } final TraversalRunnable mTraversalRunnable = new TraversalRunnable(); final class TraversalRunnable implements Runnable { @Override public void run() { doTraversal(); } } void doTraversal() { if (mTraversalScheduled) { mTraversalScheduled = false; mHandler.getLooper().getQueue().removeSyncBarrier(mTraversalBarrier); if (mProfile) { Debug.startMethodTracing("ViewAncestor"); } // 关键代码，执行ViewTree遍历 performTraversals(); if (mProfile) { Debug.stopMethodTracing(); mProfile = false; } } }</code></pre> <p>上述代码中，将会之后handler，之后会调用mTraversalRunnable类，从而调用doTraversal方法，最后调用performTraversals()执行ViewTree的遍历。</p> <p>现在继续查看ViewRootImpl#performTraversals()方法。</p> <pre> <code class="language-java">private void performTraversals() { ... if (!cancelDraw && !newSurface) { if (!skipDraw || mReportNextDraw) { if (mPendingTransitions != null && mPendingTransitions.size() > 0) { for (int i = 0; i < mPendingTransitions.size(); ++i) { mPendingTransitions.get(i).startChangingAnimations(); } mPendingTransitions.clear(); } // 关键代码 performDraw(); } } ... } private void performDraw() { ... final boolean fullRedrawNeeded = mFullRedrawNeeded; mFullRedrawNeeded = false; mIsDrawing = true; Trace.traceBegin(Trace.TRACE_TAG_VIEW, "draw"); try { // 关键代码 draw(fullRedrawNeeded); } finally { mIsDrawing = false; Trace.traceEnd(Trace.TRACE_TAG_VIEW); } ... }</code></pre> <p>在其中进行View的是否可见，是否为surfasce，是否正在绘制，是否存在于删除列表中等判断，之后调用performDraw()开始执行绘制。在performDraw()又调用了ViewRootImpl的draw方法，并传递了fullRedrawNeeded参数，此参数源自mFullRedrawNeeded成员变量，用于表示是否需要重新绘制全部的View。现在继续看看ViewRootImpl#draw源码。</p> <pre> <code class="language-java">private void draw(boolean fullRedrawNeeded) { Surface surface = mSurface; ... // 获取mDirty，该值表示需要重绘的区域 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; } // 如果为ture，则设置dirty区域为全屏 if (fullRedrawNeeded) { mAttachInfo.mIgnoreDirtyState = true; dirty.set(0, 0, (int) (mWidth * appScale + 0.5f), (int) (mHeight * appScale + 0.5f)); } ... // 重绘区域、动画判断 // 硬件渲染判断 // 关键代码 if (!drawSoftware(surface, mAttachInfo, xOffset, yOffset, scalingRequired, dirty)) { return; } ... }</code></pre> <p>在draw方法中，根据传如fullRedrawNeeded参数，设置需要重绘的dirty区域，最后调用drawSoftware方法，把参数传递进去，现在继续看ViewRootImpl#drawSoftware源码。</p> <pre> <code class="language-java">private boolean drawSoftware(Surface surface, AttachInfo attachInfo, int xoff, int yoff, boolean scalingRequired, Rect dirty) { ... try { if (!canvas.isOpaque() || yoff != 0 || xoff != 0) { canvas.drawColor(0, PorterDuff.Mode.CLEAR); } dirty.setEmpty(); mIsAnimating = false; mView.mPrivateFlags |= View.PFLAG_DRAWN; try { canvas.translate(-xoff, -yoff); if (mTranslator != null) { mTranslator.translateCanvas(canvas); } canvas.setScreenDensity(scalingRequired ? mNoncompatDensity : 0); attachInfo.mSetIgnoreDirtyState = false; // 关键代码，mView为DecorView，开启View绘制 mView.draw(canvas); drawAccessibilityFocusedDrawableIfNeeded(canvas); } finally { if (!attachInfo.mSetIgnoreDirtyState) { // Only clear the flag if it was not set during the mView.draw() call attachInfo.mIgnoreDirtyState = false; } } } ... }</code></pre> <p>上述代码中，首先对canvas进行一些属性设置，包括色块、平移等。之后调用mView.draw(canvas)方法，开始对View进行绘制。mView就是window中的顶级视图DecorView(这个坑会在之后的文章中说明，这里当做一个顶级的ViewGroup即可)。</p> <h3>2、绘制流程</h3> <p>DecorView继承自FrameLayout，而ViewGroup的draw方法继承自View，so，所以我们直接看View#draw即可。</p> <pre> <code class="language-java">public void draw(Canvas canvas) { final int privateFlags = mPrivateFlags; final boolean dirtyOpaque = (privateFlags & PFLAG_DIRTY_MASK) == PFLAG_DIRTY_OPAQUE && (mAttachInfo == null || !mAttachInfo.mIgnoreDirtyState); mPrivateFlags = (privateFlags & ~PFLAG_DIRTY_MASK) | PFLAG_DRAWN; /* * Draw traversal performs several drawing steps which must be executed * in the appropriate order: * * 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) */ // Step 1, draw the background, if needed int saveCount; if (!dirtyOpaque) { drawBackground(canvas); } // skip step 2 & 5 if possible (common case) final int viewFlags = mViewFlags; boolean horizontalEdges = (viewFlags & FADING_EDGE_HORIZONTAL) != 0; boolean verticalEdges = (viewFlags & FADING_EDGE_VERTICAL) != 0; if (!verticalEdges && !horizontalEdges) { // Step 3, draw the content if (!dirtyOpaque) onDraw(canvas); // Step 4, draw the children dispatchDraw(canvas); // Overlay is part of the content and draws beneath Foreground if (mOverlay != null && !mOverlay.isEmpty()) { mOverlay.getOverlayView().dispatchDraw(canvas); } // Step 6, draw decorations (foreground, scrollbars) onDrawForeground(canvas); // we're done... return; } ... }</code></pre> <p>draw方法中，官方对其的步骤进行了清晰的注释，我们来看下流程，在执行流程之前会检查绘制区域是否透明:</p> <p>* 1、绘制View背景，如果透明则不绘制</p> <p>* 2、如果需要，则保存画布的图层</p> <p>* 3、绘制View内容，如果透明则不绘制</p> <p>* 4、绘制子View————这个很重要</p> <p>* 5、如果需要，则绘制View的褪色边缘和恢复图层</p> <p>* 6、绘制装饰滚动条</p> <p>这里最重要的步骤是第四步，绘制子View，现在我们来看下这个ViewGroup#dispatchDraw(canvas)方法，注意这里的View是一个DecorView，所以要在ViewGroup中去查看这个方法，View中的这个方法是一个空方法。</p> <pre> <code class="language-java">protected void dispatchDraw(Canvas canvas) { ... for (int i = 0; i < childrenCount; i++) { while (transientIndex >= 0 && mTransientIndices.get(transientIndex) == i) { final View transientChild = mTransientViews.get(transientIndex); if ((transientChild.mViewFlags & VISIBILITY_MASK) == VISIBLE || transientChild.getAnimation() != null) { more |= drawChild(canvas, transientChild, drawingTime); } transientIndex++; if (transientIndex >= transientCount) { transientIndex = -1; } } int childIndex = customOrder ? getChildDrawingOrder(childrenCount, i) : i; final View child = (preorderedList == null) ? children[childIndex] : preorderedList.get(childIndex); if ((child.mViewFlags & VISIBILITY_MASK) == VISIBLE || child.getAnimation() != null) { more |= drawChild(canvas, child, drawingTime); } } while (transientIndex >= 0) { // there may be additional transient views after the normal views final View transientChild = mTransientViews.get(transientIndex); if ((transientChild.mViewFlags & VISIBILITY_MASK) == VISIBLE || transientChild.getAnimation() != null) { more |= drawChild(canvas, transientChild, drawingTime); } transientIndex++; if (transientIndex >= transientCount) { break; } } ... }</code></pre> <p>上述代码对所有的子View进行遍历，并调用ViewGroup#drawChild方法。</p> <pre> <code class="language-java">protected boolean drawChild(Canvas canvas, View child, long drawingTime) { return child.draw(canvas, this, drawingTime); }</code></pre> <p>drawChild又调用了子View的draw方法，这样绘制就传递了下去，当然这个draw方法和之前这一小节一开始介绍的View#draw方法并不一样，我们来看看</p> <pre> <code class="language-java">boolean draw(Canvas canvas, ViewGroup parent, long drawingTime) { ... if (!drawingWithRenderNode) { computeScroll(); sx = mScrollX; sy = mScrollY; } ... if (!drawingWithDrawingCache) { if (drawingWithRenderNode) { mPrivateFlags &= ~PFLAG_DIRTY_MASK; ((DisplayListCanvas) canvas).drawRenderNode(renderNode); } else { // Fast path for layouts with no backgrounds if ((mPrivateFlags & PFLAG_SKIP_DRAW) == PFLAG_SKIP_DRAW) { mPrivateFlags &= ~PFLAG_DIRTY_MASK; dispatchDraw(canvas); } else { draw(canvas); } } } else if (cache != null) { mPrivateFlags &= ~PFLAG_DIRTY_MASK; if (layerType == LAYER_TYPE_NONE) { // no layer paint, use temporary paint to draw bitmap Paint cachePaint = parent.mCachePaint; if (cachePaint == null) { cachePaint = new Paint(); cachePaint.setDither(false); parent.mCachePaint = cachePaint; } cachePaint.setAlpha((int) (alpha * 255)); canvas.drawBitmap(cache, 0.0f, 0.0f, cachePaint); } else { // use layer paint to draw the bitmap, merging the two alphas, but also restore int layerPaintAlpha = mLayerPaint.getAlpha(); mLayerPaint.setAlpha((int) (alpha * layerPaintAlpha)); canvas.drawBitmap(cache, 0.0f, 0.0f, mLayerPaint); mLayerPaint.setAlpha(layerPaintAlpha); } } ... }</code></pre> <p>上述代码会先判断之前是否进行过了绘制，如果没有则进入快速绘制通道，对没有背景的View进行绘制。判断是否需要跳过自身的draw绘制方法，如果跳过则进入dispatchDraw，不跳过则进入当前View的draw方法，即这一小节开头的draw方法，就此形成了循环。同时我们在这里看到了 <strong>computeScroll()</strong> 方法，也就印证了上一篇文章对于弹性滑动过程的描述。</p> <p>流程图如下:</p> <p><img src="https://simg.open-open.com/show/bdf2af9016bf60de66c8fcbaac96cbbc.png"></p> <h2>三、小结</h2> <p>本文对上一篇遗留的问题postInvalidate与invalidate的区别进行了回答与分析，对invalidate的传递流程，以及View的绘制流程进行了源码分析，解答了invalidate是如何调用computeScroll()的问题。如果在阅读过程中，有任何疑问与问题，欢迎与我联系。</p> <p> </p> <p> </p> <p>来自：http://www.idtkm.com/customview/customview9/</p> <p> </p>