http://www.oschina.net/question/163910_27566
在Android的佈局體系中，父View負責刷新、佈局顯示子View；而當子View需要刷新時，則是通知父View來完成。這種處理邏輯在View的代碼中明確的表現出來：
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public
void
invalidate() { final
ViewParent p = mParent; final
AttachInfo ai = mAttachInfo; if
(p != null
&& ai != null)
{ final
Rect r = ai.mTmpInvalRect; //
設置刷新區域爲自己的尺寸 r.set(0,
0,
mRight - mLeft, mBottom - mTop); p.invalidateChild(this,
r); }} |
子View調用invalidate時，首先找到自己父View(View的成員變量mParent記錄自己的父View)，然後將AttachInfo中保存的信息告訴父View刷新自己。
View的父子關係的建立分爲兩種情況：
1) View加入ViewGroup中
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private
void
addViewInner(View child, int
index, LayoutParams params, boolean
preventRequestLayout) { ..... //
tell our children if
(preventRequestLayout) { child.assignParent(this); }
else
{ child.mParent
= this; } .....}public
void
setView(View view, WindowManager.LayoutParams attrs, View panelParentView){ ..... view.assignParent(this); ....} |
AttachInfo是在View第一次attach到Window時，ViewRoot傳給自己的子View的。這個AttachInfo之後，會順着佈局體系一直傳遞到最底層的View。
View.java
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void
dispatchAttachedToWindow(AttachInfo info, int
visibility) { mAttachInfo
= info; .....} |
ViewGroup.java
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void
dispatchAttachedToWindow(AttachInfo info, int
visibility) { super.dispatchAttachedToWindow(info,
visibility); for
(int
i = 0;
i < count; i++) { children[i].dispatchAttachedToWindow(info,
visibility); }} |
並且在新的View被加入ViewGroup時，也會將該AttachInfo傳給加入的View
ViewGroup.java
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private
void
addViewInner(View child, int
index, LayoutParams params, boolean
preventRequestLayout) { child.dispatchAttachedToWindow(mAttachInfo,
(mViewFlags&VISIBILITY_MASK)); } |
到這裏明白了mParent與AttachInfo代表的意義，可以繼續刷新過程的分析。
在invalidate中，調用父View的invalidateChild，這是一個從第向上回溯的過程，每一層的父View都將自己的顯示區域與傳入的刷新Rect做交集。
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public
final
void
invalidateChild(View child, final
Rect dirty) { ViewParent
parent = this; final
AttachInfo attachInfo = mAttachInfo; if
(attachInfo != null)
{ final
int[]
location = attachInfo.mInvalidateChildLocation; //
需要刷新的子View的位置 location[CHILD_LEFT_INDEX]
= child.mLeft; location[CHILD_TOP_INDEX]
= child.mTop; //
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; //
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 final
int
opaqueFlag = isOpaque ? DIRTY_OPAQUE : DIRTY; do
{ View
view = null; if
(parent instanceof
View) { view
= (View) parent; } if
(drawAnimation) { if
(view != null)
{ view.mPrivateFlags
|= DRAW_ANIMATION; }
else
if
(parent instanceof
ViewRoot) { ((ViewRoot)
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
&& (view.mPrivateFlags & DIRTY_MASK) != DIRTY) { view.mPrivateFlags
= (view.mPrivateFlags & ~DIRTY_MASK) | opaqueFlag; } parent
= parent.invalidateChildInParent(location, dirty); }
while
(parent != null); }} public
ViewParent invalidateChildInParent(final
int[]
location, final
Rect dirty) { if
((mPrivateFlags & DRAWN) == DRAWN) { if
((mGroupFlags & (FLAG_OPTIMIZE_INVALIDATE | FLAG_ANIMATION_DONE)) != FLAG_OPTIMIZE_INVALIDATE)
{ //
根據父View的位置，偏移刷新區域 dirty.offset(location[CHILD_LEFT_INDEX]
- mScrollX, location[CHILD_TOP_INDEX] - mScrollY); final
int
left = mLeft; final
int
top = mTop; //計算實際可刷新區域 if
(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; return
mParent; } }
else
{ mPrivateFlags
&= ~DRAWN & ~DRAWING_CACHE_VALID; location[CHILD_LEFT_INDEX]
= mLeft; location[CHILD_TOP_INDEX]
= mTop; dirty.set(0,
0,
mRight - location[CHILD_LEFT_INDEX], mBottom
- location[CHILD_TOP_INDEX]); return
mParent; } } return
null;} |
這個向上回溯的過程直到ViewRoot那裏結束，由ViewRoot對這個最終的刷新區域做刷新。
ViewRoot.java
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public
void
invalidateChild(View child, Rect dirty) { scheduleTraversals(); } |
原文鏈接：http://blog.csdn.net/dragondog/article/details/6454551