Android中invalidate() 函数详解(组合Android 4.0.4 最新源码)

Android中invalidate() 函数详解(结合Android 4.0.4 最新源码)

      invalidate()函数的主要作用是请求View树进行重绘，该函数可以由应用程序调用，或者由系统函数间接调用，例如setEnable(), setSelected(), setVisiblity()都会间接调用到invalidate()来请求View树重绘，更新View树的显示。

      注：requestLayout()和requestFocus()函数也会引起视图重绘

      下面我们通过源码来了解invalidate()函数的工作原理，首先我们来看View类中invalidate()的实现过程：

/** * Invalidate the whole view. If the view is visible, * {@link #onDraw(android.graphics.Canvas)} will be called at some point in * the future. This must be called from a UI thread. To call from a non-UI thread, * call {@link #postInvalidate()}. */ public void invalidate() { invalidate(true); }
      invalidate()函数会转而调用invalidate(true)，继续往下看：

/** * This is where the invalidate() work actually happens. A full invalidate() * causes the drawing cache to be invalidated, but this function can be called with * invalidateCache set to false to skip that invalidation step for cases that do not * need it (for example, a component that remains at the same dimensions with the same * content). * * @param invalidateCache Whether the drawing cache for this view should be invalidated as * well. This is usually true for a full invalidate, but may be set to false if the * View's contents or dimensions have not changed. */ void invalidate(boolean invalidateCache) { if (ViewDebug.TRACE_HIERARCHY) { ViewDebug.trace(this, ViewDebug.HierarchyTraceType.INVALIDATE); } if (skipInvalidate()) { return; } if ((mPrivateFlags & (DRAWN | HAS_BOUNDS)) == (DRAWN | HAS_BOUNDS) || (invalidateCache && (mPrivateFlags & DRAWING_CACHE_VALID) == DRAWING_CACHE_VALID) || (mPrivateFlags & INVALIDATED) != INVALIDATED || isOpaque() != mLastIsOpaque) { mLastIsOpaque = isOpaque(); mPrivateFlags &= ~DRAWN; mPrivateFlags |= DIRTY; if (invalidateCache) { mPrivateFlags |= INVALIDATED; mPrivateFlags &= ~DRAWING_CACHE_VALID; } final AttachInfo ai = mAttachInfo; final ViewParent p = mParent; //noinspection PointlessBooleanExpression,ConstantConditions if (!HardwareRenderer.RENDER_DIRTY_REGIONS) { if (p != null && ai != null && ai.mHardwareAccelerated) { // fast-track for GL-enabled applications; just invalidate the whole hierarchy // with a null dirty rect, which tells the ViewAncestor to redraw everything p.invalidateChild(this, null); return; } } if (p != null && ai != null) { final Rect r = ai.mTmpInvalRect; r.set(0, 0, mRight - mLeft, mBottom - mTop); // Don't call invalidate -- we don't want to internally scroll // our own bounds p.invalidateChild(this, r); } } }
      下面我们来具体进行分析invalidate(true)函数的执行流程：

            1、首先调用skipInvalidate()，该函数主要判断该View是否不需要重绘，如果不许要重绘则直接返回，不需要重绘的条件是该View不可见并且未进行动画

            2、接下来的if语句是来进一步判断View是否需要绘制，其中表达式 (mPrivateFlags & (DRAWN | HAS_BOUNDS)) == (DRAWN | HAS_BOUNDS)的意思指的是如果View需要重绘并且其大小不为0，其余几个本人也未完全理解，还望高手指点～～如果需要重绘，则处理相关标志位

            3、对于开启硬件加速的应用程序，则调用父视图的invalidateChild函数绘制整个区域，否则只绘制dirty区域（r变量所指的区域），这是一个向上回溯的过程，每一层的父View都将自己的显示区域与传入的刷新Rect做交集。

      接下来看invalidateChild()的 实现过程：

public final void invalidateChild(View child, final Rect dirty) { if (ViewDebug.TRACE_HIERARCHY) { ViewDebug.trace(this, ViewDebug.HierarchyTraceType.INVALIDATE_CHILD); } ViewParent parent = this; final AttachInfo attachInfo = mAttachInfo; if (attachInfo != null) { // If the child is drawing an animation, we want to copy this flag onto // ourselves and the parent to make sure the invalidate request goes // through final boolean drawAnimation = (child.mPrivateFlags & DRAW_ANIMATION) == DRAW_ANIMATION; if (dirty == null) { if (child.mLayerType != LAYER_TYPE_NONE) { mPrivateFlags |= INVALIDATED; mPrivateFlags &= ~DRAWING_CACHE_VALID; child.mLocalDirtyRect.setEmpty(); } do { View view = null; if (parent instanceof View) { view = (View) parent; if (view.mLayerType != LAYER_TYPE_NONE) { view.mLocalDirtyRect.setEmpty(); if (view.getParent() instanceof View) { final View grandParent = (View) view.getParent(); grandParent.mPrivateFlags |= INVALIDATED; grandParent.mPrivateFlags &= ~DRAWING_CACHE_VALID; } } if ((view.mPrivateFlags & DIRTY_MASK) != 0) { // already marked dirty - we're done break; } } if (drawAnimation) { if (view != null) { view.mPrivateFlags |= DRAW_ANIMATION; } else if (parent instanceof ViewRootImpl) { ((ViewRootImpl) parent).mIsAnimating = true; } } if (parent instanceof ViewRootImpl) { ((ViewRootImpl) parent).invalidate(); parent = null; } else if (view != null) { if ((view.mPrivateFlags & DRAWN) == DRAWN || (view.mPrivateFlags & DRAWING_CACHE_VALID) == DRAWING_CACHE_VALID) { view.mPrivateFlags &= ~DRAWING_CACHE_VALID; view.mPrivateFlags |= DIRTY; parent = view.mParent; } else { parent = null; } } } while (parent != null); } else { // Check whether the child that requests the invalidate is fully opaque final boolean isOpaque = child.isOpaque() && !drawAnimation && child.getAnimation() == null; // Mark the child as dirty, using the appropriate flag // Make sure we do not set both flags at the same time int opaqueFlag = isOpaque ? DIRTY_OPAQUE : DIRTY; if (child.mLayerType != LAYER_TYPE_NONE) { mPrivateFlags |= INVALIDATED; mPrivateFlags &= ~DRAWING_CACHE_VALID; child.mLocalDirtyRect.union(dirty); } final int[] location = attachInfo.mInvalidateChildLocation; location[CHILD_LEFT_INDEX] = child.mLeft; location[CHILD_TOP_INDEX] = child.mTop; Matrix childMatrix = child.getMatrix(); if (!childMatrix.isIdentity()) { RectF boundingRect = attachInfo.mTmpTransformRect; boundingRect.set(dirty); //boundingRect.inset(-0.5f, -0.5f); childMatrix.mapRect(boundingRect); dirty.set((int) (boundingRect.left - 0.5f), (int) (boundingRect.top - 0.5f), (int) (boundingRect.right + 0.5f), (int) (boundingRect.bottom + 0.5f)); } do { View view = null; if (parent instanceof View) { view = (View) parent; if (view.mLayerType != LAYER_TYPE_NONE && view.getParent() instanceof View) { final View grandParent = (View) view.getParent(); grandParent.mPrivateFlags |= INVALIDATED; grandParent.mPrivateFlags &= ~DRAWING_CACHE_VALID; } } if (drawAnimation) { if (view != null) { view.mPrivateFlags |= 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 = DIRTY; } if ((view.mPrivateFlags & DIRTY_MASK) != DIRTY) { view.mPrivateFlags = (view.mPrivateFlags & ~DIRTY_MASK) | opaqueFlag; } } 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, (int) boundingRect.top, (int) (boundingRect.right + 0.5f), (int) (boundingRect.bottom + 0.5f)); } } } while (parent != null); } } }

      大概流程如下，我们主要关注dirty区域不是null（非硬件加速）的情况：

            1、判断子视图是否是不透明的（不透明的条件是isOpaque()返回true，视图未进行动画以及child.getAnimation() == null），并将判断结果保存到变量isOpaque中，如果不透明则将变量opaqueFlag设置为DIRTY_OPAQUE，否则设置为DIRTY。

            2、定义location保存子视图的左上角坐标

            3、如果子视图正在动画，那么父视图也要添加动画标志，如果父视图是ViewGroup，那么给mPrivateFlags添加DRAW_ANIMATION标识，如果父视图是ViewRoot，则给其内部变量mIsAnimating赋值为true

            4、设置dirty标识，如果子视图是不透明的，则父视图设置为DIRTY_OPAQUE，否则设置为DIRTY

            5、调用parent.invalidateChildInparent()，这里的parent有可能是ViewGroup，也有可能是ViewRoot（最后一次while循环），首先来看ViewGroup, ViewGroup中该函数的主要作用是对dirty区域进行计算

      以上过程的主体是一个do{}while{}循环，不断的将子视图的dirty区域与父视图做运算来确定最终要重绘的dirty区域，最终循环到ViewRoot（ViewRoot的parent为null）为止，并将dirty区域保存到ViewRoot的mDirty变量中

/** * Don't call or override this method. It is used for the implementation of * the view hierarchy. * * This implementation returns null if this ViewGroup does not have a parent, * if this ViewGroup is already fully invalidated or if the dirty rectangle * does not intersect with this ViewGroup's bounds. */ public ViewParent invalidateChildInParent(final int[] location, final Rect dirty) { if (ViewDebug.TRACE_HIERARCHY) { ViewDebug.trace(this, ViewDebug.HierarchyTraceType.INVALIDATE_CHILD_IN_PARENT); } if ((mPrivateFlags & DRAWN) == DRAWN || (mPrivateFlags & DRAWING_CACHE_VALID) == DRAWING_CACHE_VALID) { if ((mGroupFlags & (FLAG_OPTIMIZE_INVALIDATE | FLAG_ANIMATION_DONE)) != FLAG_OPTIMIZE_INVALIDATE) { dirty.offset(location[CHILD_LEFT_INDEX] - mScrollX, location[CHILD_TOP_INDEX] - mScrollY); final int left = mLeft; final int top = mTop; if ((mGroupFlags & FLAG_CLIP_CHILDREN) != FLAG_CLIP_CHILDREN || dirty.intersect(0, 0, mRight - left, mBottom - top) || (mPrivateFlags & DRAW_ANIMATION) == DRAW_ANIMATION) { mPrivateFlags &= ~DRAWING_CACHE_VALID; location[CHILD_LEFT_INDEX] = left; location[CHILD_TOP_INDEX] = top; if (mLayerType != LAYER_TYPE_NONE) { mLocalDirtyRect.union(dirty); } return mParent; } } else { mPrivateFlags &= ~DRAWN & ~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) { mLocalDirtyRect.union(dirty); } return mParent; } } return null; }
      该函数首先调用offset将子视图的坐标位置转换为在父视图（当前视图）的显示位置，这里主要考虑scroll后导致子视图在父视图中的显示区域会发生变化，接着调用union函数求得当前视图与子视图的交集,求得的交集必定是小于dirty的范围，因为子视图的dirty区域有可能超出其父视图（当前视图）的范围，最后返回当前视图的父视图。

      再来看ViewRoot中invalidateChildInparent的执行过程：

public ViewParent invalidateChildInParent(final int[] location, final Rect dirty) { invalidateChild(null, dirty); return null; }
      该函数仅仅调用了ViewRoot的invalidateChild，下面继续看invalidateChild的源码：

public void invalidateChild(View child, Rect dirty) { checkThread(); if (DEBUG_DRAW) Log.v(TAG, "Invalidate child: " + dirty); if (dirty == null) { // Fast invalidation for GL-enabled applications; GL must redraw everything invalidate(); return; } 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); } } if (!mDirty.isEmpty() && !mDirty.contains(dirty)) { mAttachInfo.mSetIgnoreDirtyState = true; mAttachInfo.mIgnoreDirtyState = true; } mDirty.union(dirty); if (!mWillDrawSoon) { scheduleTraversals(); } }

      具体分析如下：

            1、判断此次调用是否在UI线程中进行

            2、将dirty的坐标位置转换为ViewRoot的屏幕显示区域

            3、更新mDirty变量，并调用scheduleTraversals发起重绘请求

      至此一次invalidate()就结束了

      总结：invalidate主要给需要重绘的视图添加DIRTY标记，并通过和父视图的矩形运算求得真正需要绘制的区域，并保存在ViewRoot中的mDirty变量中，最后调用scheduleTraversals发起重绘请求，scheduleTraversals会发送一个异步消息，最终调用performTraversals()执行重绘，performTraversals()的具体过程以后再分析。

    以上所有代码基于Android 4.0.4，并结合《Android内核剖析》分析总结而成，源码中涉及到的部分细节本人也未完全理解，还望高手指点~~