android invalidate 执行流程详解

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：

1. /**
2. * Invalidate the whole view. If the view is visible,
3. * [url=mailto:{@link]{@link[/url] #onDraw(android.graphics.Canvas)} will be called at some point in
4. * the future. This must be called from a UI thread. To call from a non-UI thread,
5. * call [url=mailto:{@link]{@link[/url] #postInvalidate()}.
6. */
7. public void invalidate() {
8. invalidate(true);
9. }

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

1. /**
2. * This is where the invalidate() work actually happens. A full invalidate()
3. * causes the drawing cache to be invalidated, but this function can be called with
4. * invalidateCache set to false to skip that invalidation step for cases that do not
5. * need it (for example, a component that remains at the same dimensions with the same
6. * content).
7. *
8. * @param invalidateCache Whether the drawing cache for this view should be invalidated as
9. * well. This is usually true for a full invalidate, but may be set to false if the
10. * View's contents or dimensions have not changed.
11. */
12. void invalidate(boolean invalidateCache) {
13. if (ViewDebug.TRACE_HIERARCHY) {
14. ViewDebug.trace(this, ViewDebug.HierarchyTraceType.INVALIDATE);
15. }
16. if (skipInvalidate()) {
17. return;
18. }
19. if ((mPrivateFlags & (DRAWN | HAS_BOUNDS)) == (DRAWN | HAS_BOUNDS) ||
20. (invalidateCache && (mPrivateFlags & DRAWING_CACHE_VALID) == DRAWING_CACHE_VALID) ||
21. (mPrivateFlags & INVALIDATED) != INVALIDATED || isOpaque() != mLastIsOpaque) {
22. mLastIsOpaque = isOpaque();
23. mPrivateFlags &= ~DRAWN;
24. mPrivateFlags |= DIRTY;
25. if (invalidateCache) {
26. mPrivateFlags |= INVALIDATED;
27. mPrivateFlags &= ~DRAWING_CACHE_VALID;
28. }
29. final AttachInfo ai = mAttachInfo;
30. final ViewParent p = mParent;
31. //noinspection PointlessBooleanExpression,ConstantConditions
32. if (!HardwareRenderer.RENDER_DIRTY_REGIONS) {
33. if (p != null && ai != null && ai.mHardwareAccelerated) {
34. // fast-track for GL-enabled applications; just invalidate the whole hierarchy
35. // with a null dirty rect, which tells the ViewAncestor to redraw everything
36. p.invalidateChild(this, null);
37. return;
38. }
39. }
40. if (p != null && ai != null) {
41. final Rect r = ai.mTmpInvalRect;
42. r.set(0, 0, mRight - mLeft, mBottom - mTop);
43. // Don't call invalidate -- we don't want to internally scroll
44. // our own bounds
45. p.invalidateChild(this, r);
46. }
47. }
48. }

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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：

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. }

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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

1. /**
2. * Don't call or override this method. It is used for the implementation of
3. * the view hierarchy.
4. *
5. * This implementation returns null if this ViewGroup does not have a parent,
6. * if this ViewGroup is already fully invalidated or if the dirty rectangle
7. * does not intersect with this ViewGroup's bounds.
8. */
9. public ViewParent invalidateChildInParent(final int[] location, final Rect dirty) {
10. if (ViewDebug.TRACE_HIERARCHY) {
11. ViewDebug.trace(this, ViewDebug.HierarchyTraceType.INVALIDATE_CHILD_IN_PARENT);
12. }
13. if ((mPrivateFlags & DRAWN) == DRAWN ||
14. (mPrivateFlags & DRAWING_CACHE_VALID) == DRAWING_CACHE_VALID) {
15. if ((mGroupFlags & (FLAG_OPTIMIZE_INVALIDATE | FLAG_ANIMATION_DONE)) !=
16. FLAG_OPTIMIZE_INVALIDATE) {
17. dirty.offset(location[CHILD_LEFT_INDEX] - mScrollX,
18. location[CHILD_TOP_INDEX] - mScrollY);
19. final int left = mLeft;
20. final int top = mTop;
21. if ((mGroupFlags & FLAG_CLIP_CHILDREN) != FLAG_CLIP_CHILDREN ||
22. dirty.intersect(0, 0, mRight - left, mBottom - top) ||
23. (mPrivateFlags & DRAW_ANIMATION) == DRAW_ANIMATION) {
24. mPrivateFlags &= ~DRAWING_CACHE_VALID;
25. location[CHILD_LEFT_INDEX] = left;
26. location[CHILD_TOP_INDEX] = top;
27. if (mLayerType != LAYER_TYPE_NONE) {
28. mLocalDirtyRect.union(dirty);
29. }
30. return mParent;
31. }
32. } else {
33. mPrivateFlags &= ~DRAWN & ~DRAWING_CACHE_VALID;
34. location[CHILD_LEFT_INDEX] = mLeft;
35. location[CHILD_TOP_INDEX] = mTop;
36. if ((mGroupFlags & FLAG_CLIP_CHILDREN) == FLAG_CLIP_CHILDREN) {
37. dirty.set(0, 0, mRight - mLeft, mBottom - mTop);
38. } else {
39. // in case the dirty rect extends outside the bounds of this container
40. dirty.union(0, 0, mRight - mLeft, mBottom - mTop);
41. }
42. if (mLayerType != LAYER_TYPE_NONE) {
43. mLocalDirtyRect.union(dirty);
44. }
45. return mParent;
46. }
47. }
48. return null;
49. }

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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：

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

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

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. }

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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。