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:

[java] view plaincopy

  1. /**
    • 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()}.
  2. */
  3. public void invalidate() {
  4. invalidate(true);
  5. }

invalidate()函数会转而调用invalidate(true),继续往下看:

[java] view plaincopy

  1. /**
    • 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).
  2. *
    • @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.
  3. */
  4. void invalidate(boolean invalidateCache) {
  5. if (ViewDebug.TRACE_HIERARCHY) {
  6. ViewDebug.trace(this, ViewDebug.HierarchyTraceType.INVALIDATE);
  7. }

  8. if (skipInvalidate()) {

  9. return;
  10. }
  11. if ((mPrivateFlags & (DRAWN | HAS_BOUNDS)) == (DRAWN | HAS_BOUNDS) ||
  12. (invalidateCache && (mPrivateFlags & DRAWING_CACHE_VALID) == DRAWING_CACHE_VALID) ||
  13. (mPrivateFlags & INVALIDATED) != INVALIDATED || isOpaque() != mLastIsOpaque) {
  14. mLastIsOpaque = isOpaque();
  15. mPrivateFlags &= ~DRAWN;
  16. mPrivateFlags |= DIRTY;
  17. if (invalidateCache) {
  18. mPrivateFlags |= INVALIDATED;
  19. mPrivateFlags &= ~DRAWING_CACHE_VALID;
  20. }
  21. final AttachInfo ai = mAttachInfo;
  22. final ViewParent p = mParent;
  23. //noinspection PointlessBooleanExpression,ConstantConditions
  24. if (!HardwareRenderer.RENDER_DIRTY_REGIONS) {
  25. if (p != null && ai != null && ai.mHardwareAccelerated) {
  26. // fast-track for GL-enabled applications; just invalidate the whole hierarchy
  27. // with a null dirty rect, which tells the ViewAncestor to redraw everything
  28. p.invalidateChild(this, null);
  29. return;
  30. }
  31. }

  32. if (p != null && ai != null) {

  33. final Rect r = ai.mTmpInvalRect;
  34. r.set(0, 0, mRight - mLeft, mBottom - mTop);
  35. // Don’t call invalidate – we don’t want to internally scroll
  36. // our own bounds
  37. p.invalidateChild(this, r);
  38. }
  39. }
  40. }

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:

[java] view plaincopy

  1. public final void invalidateChild(View child, final Rect dirty) {
  2. if (ViewDebug.TRACE_HIERARCHY) {
  3. ViewDebug.trace(this, ViewDebug.HierarchyTraceType.INVALIDATE_CHILD);
  4. }

  5. ViewParent parent = this;

  6. final AttachInfo attachInfo = mAttachInfo;

  7. if (attachInfo != null) {
  8. // If the child is drawing an animation, we want to copy this flag onto
  9. // ourselves and the parent to make sure the invalidate request goes
  10. // through
  11. final boolean drawAnimation = (child.mPrivateFlags & DRAW_ANIMATION) == DRAW_ANIMATION;

  12. if (dirty == null) {

  13. if (child.mLayerType != LAYER_TYPE_NONE) {
  14. mPrivateFlags |= INVALIDATED;
  15. mPrivateFlags &= ~DRAWING_CACHE_VALID;
  16. child.mLocalDirtyRect.setEmpty();
  17. }
  18. do {
  19. View view = null;
  20. if (parent instanceof View) {
  21. view = (View) parent;
  22. if (view.mLayerType != LAYER_TYPE_NONE) {
  23. view.mLocalDirtyRect.setEmpty();
  24. if (view.getParent() instanceof View) {
  25. final View grandParent = (View) view.getParent();
  26. grandParent.mPrivateFlags |= INVALIDATED;
  27. grandParent.mPrivateFlags &= ~DRAWING_CACHE_VALID;
  28. }
  29. }
  30. if ((view.mPrivateFlags & DIRTY_MASK) != 0) {
  31. // already marked dirty - we’re done
  32. break;
  33. }
  34. }

  35. if (drawAnimation) {

  36. if (view != null) {
  37. view.mPrivateFlags |= DRAW_ANIMATION;
  38. } else if (parent instanceof ViewRootImpl) {
  39. ((ViewRootImpl) parent).mIsAnimating = true;
  40. }
  41. }

  42. if (parent instanceof ViewRootImpl) {

  43. ((ViewRootImpl) parent).invalidate();
  44. parent = null;
  45. } else if (view != null) {
  46. if ((view.mPrivateFlags & DRAWN) == DRAWN ||
  47. (view.mPrivateFlags & DRAWING_CACHE_VALID) == DRAWING_CACHE_VALID) {
  48. view.mPrivateFlags &= ~DRAWING_CACHE_VALID;
  49. view.mPrivateFlags |= DIRTY;
  50. parent = view.mParent;
  51. } else {
  52. parent = null;
  53. }
  54. }
  55. } while (parent != null);
  56. } else {
  57. // Check whether the child that requests the invalidate is fully opaque
  58. final boolean isOpaque = child.isOpaque() && !drawAnimation &&
  59. child.getAnimation() == null;
  60. // Mark the child as dirty, using the appropriate flag
  61. // Make sure we do not set both flags at the same time
  62. int opaqueFlag = isOpaque ? DIRTY_OPAQUE : DIRTY;

  63. if (child.mLayerType != LAYER_TYPE_NONE) {

  64. mPrivateFlags |= INVALIDATED;
  65. mPrivateFlags &= ~DRAWING_CACHE_VALID;
  66. child.mLocalDirtyRect.union(dirty);
  67. }

  68. final int[] location = attachInfo.mInvalidateChildLocation;

  69. location[CHILD_LEFT_INDEX] = child.mLeft;
  70. location[CHILD_TOP_INDEX] = child.mTop;
  71. Matrix childMatrix = child.getMatrix();
  72. if (!childMatrix.isIdentity()) {
  73. RectF boundingRect = attachInfo.mTmpTransformRect;
  74. boundingRect.set(dirty);
  75. //boundingRect.inset(-0.5f, -0.5f);
  76. childMatrix.mapRect(boundingRect);
  77. dirty.set((int) (boundingRect.left - 0.5f),
  78. (int) (boundingRect.top - 0.5f),
  79. (int) (boundingRect.right + 0.5f),
  80. (int) (boundingRect.bottom + 0.5f));
  81. }

  82. do {

  83. View view = null;
  84. if (parent instanceof View) {
  85. view = (View) parent;
  86. if (view.mLayerType != LAYER_TYPE_NONE &&
  87. view.getParent() instanceof View) {
  88. final View grandParent = (View) view.getParent();
  89. grandParent.mPrivateFlags |= INVALIDATED;
  90. grandParent.mPrivateFlags &= ~DRAWING_CACHE_VALID;
  91. }
  92. }

  93. if (drawAnimation) {

  94. if (view != null) {
  95. view.mPrivateFlags |= DRAW_ANIMATION;
  96. } else if (parent instanceof ViewRootImpl) {
  97. ((ViewRootImpl) parent).mIsAnimating = true;
  98. }
  99. }

  100. // If the parent is dirty opaque or not dirty, mark it dirty with the opaque

  101. // flag coming from the child that initiated the invalidate
  102. if (view != null) {
  103. if ((view.mViewFlags & FADING_EDGE_MASK) != 0 &&
  104. view.getSolidColor() == 0) {
  105. opaqueFlag = DIRTY;
  106. }
  107. if ((view.mPrivateFlags & DIRTY_MASK) != DIRTY) {
  108. view.mPrivateFlags = (view.mPrivateFlags & ~DIRTY_MASK) | opaqueFlag;
  109. }
  110. }

  111. parent = parent.invalidateChildInParent(location, dirty);

  112. if (view != null) {
  113. // Account for transform on current parent
  114. Matrix m = view.getMatrix();
  115. if (!m.isIdentity()) {
  116. RectF boundingRect = attachInfo.mTmpTransformRect;
  117. boundingRect.set(dirty);
  118. m.mapRect(boundingRect);
  119. dirty.set((int) boundingRect.left, (int) boundingRect.top,
  120. (int) (boundingRect.right + 0.5f),
  121. (int) (boundingRect.bottom + 0.5f));
  122. }
  123. }
  124. } while (parent != null);
  125. }
  126. }
  127. }

    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

[java] view plaincopy

  1. /**
    • Don’t call or override this method. It is used for the implementation of
    • the view hierarchy.
  2. *
    • 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.
  3. */
  4. public ViewParent invalidateChildInParent(final int[] location, final Rect dirty) {
  5. if (ViewDebug.TRACE_HIERARCHY) {
  6. ViewDebug.trace(this, ViewDebug.HierarchyTraceType.INVALIDATE_CHILD_IN_PARENT);
  7. }

  8. if ((mPrivateFlags & DRAWN) == DRAWN ||

  9. (mPrivateFlags & DRAWING_CACHE_VALID) == DRAWING_CACHE_VALID) {
  10. if ((mGroupFlags & (FLAG_OPTIMIZE_INVALIDATE | FLAG_ANIMATION_DONE)) !=
  11. FLAG_OPTIMIZE_INVALIDATE) {
  12. dirty.offset(location[CHILD_LEFT_INDEX] - mScrollX,
  13. location[CHILD_TOP_INDEX] - mScrollY);

  14. final int left = mLeft;

  15. final int top = mTop;

  16. if ((mGroupFlags & FLAG_CLIP_CHILDREN) != FLAG_CLIP_CHILDREN ||

  17. dirty.intersect(0, 0, mRight - left, mBottom - top) ||
  18. (mPrivateFlags & DRAW_ANIMATION) == DRAW_ANIMATION) {
  19. mPrivateFlags &= ~DRAWING_CACHE_VALID;

  20. location[CHILD_LEFT_INDEX] = left;

  21. location[CHILD_TOP_INDEX] = top;

  22. if (mLayerType != LAYER_TYPE_NONE) {

  23. mLocalDirtyRect.union(dirty);
  24. }

  25. return mParent;

  26. }
  27. } else {
  28. mPrivateFlags &= ~DRAWN & ~DRAWING_CACHE_VALID;

  29. location[CHILD_LEFT_INDEX] = mLeft;

  30. location[CHILD_TOP_INDEX] = mTop;
  31. if ((mGroupFlags & FLAG_CLIP_CHILDREN) == FLAG_CLIP_CHILDREN) {
  32. dirty.set(0, 0, mRight - mLeft, mBottom - mTop);
  33. } else {
  34. // in case the dirty rect extends outside the bounds of this container
  35. dirty.union(0, 0, mRight - mLeft, mBottom - mTop);
  36. }

  37. if (mLayerType != LAYER_TYPE_NONE) {

  38. mLocalDirtyRect.union(dirty);
  39. }

  40. return mParent;

  41. }
  42. }

  43. return null;

  44. }

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:

[java] view plaincopy

  1. public ViewParent invalidateChildInParent(final int[] location, final Rect dirty) {
  2. invalidateChild(null, dirty);
  3. return null;
  4. }

该函数仅仅调用了ViewRoot的invalidateChild,下面继续看invalidateChild的源码:

[java] view plaincopy

  1. public void invalidateChild(View child, Rect dirty) {
  2. checkThread();
  3. if (DEBUG_DRAW) Log.v(TAG, “Invalidate child: “ + dirty);
  4. if (dirty == null) {
  5. // Fast invalidation for GL-enabled applications; GL must redraw everything
  6. invalidate();
  7. return;
  8. }
  9. if (mCurScrollY != 0 || mTranslator != null) {
  10. mTempRect.set(dirty);
  11. dirty = mTempRect;
  12. if (mCurScrollY != 0) {
  13. dirty.offset(0, -mCurScrollY);
  14. }
  15. if (mTranslator != null) {
  16. mTranslator.translateRectInAppWindowToScreen(dirty);
  17. }
  18. if (mAttachInfo.mScalingRequired) {
  19. dirty.inset(-1, -1);
  20. }
  21. }
  22. if (!mDirty.isEmpty() && !mDirty.contains(dirty)) {
  23. mAttachInfo.mSetIgnoreDirtyState = true;
  24. mAttachInfo.mIgnoreDirtyState = true;
  25. }
  26. mDirty.union(dirty);
  27. if (!mWillDrawSoon) {
  28. scheduleTraversals();
  29. }
  30. }

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~~