Android view 刷新流程
浏览数：54 /
时间：2015年06月11日
参考 http://www.2cto.com/kf/201307/226138.html
http://blog.csdn.net/chenzhiqin20/article/details/8628952
1.刷新方法
1.不使用多线程和双缓冲
ui线程中调用invalidate() {关于invalidate的解释:当调用线程处于空闲状态时，会调用onDraw，刷新界面，也就是说，该函数仅是标记当前界面过期，并不直接负责刷新界面；}方法即可。系统会自动调用View的onDraw()方法。
2.使用多线程但不使用双缓冲
使用handler ，在handler
的handlemsg方法中调用invalidate
3.使用多线程和双缓冲
Android中SurfaceView是View的子类，她同时也实现了双缓冲。可以定义一个她的子类并实现SurfaceHolder.Callback接口。由于实现SurfaceHolder.Callback接口，新线程就不需要android.os.Handler帮忙了。SurfaceHolder中lockCanvas()方法可以锁定画布，绘制完新的图像后调用unlockCanvasAndPost(canvas)解锁（显示）
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public class MySurfaceView extends
SurfaceView implements
SurfaceHolder.Callback { private
SurfaceHolder holder; public
MySurfaceView(Context context, AttributeSet attrs) { super(context, attrs); } public
MySurfaceView(Context context) { super(context); holder = this.getHolder(); holder.addCallback(this); this.setLongClickable(true);// 不设置将无法捕捉onFling()事件 setFocusable(true);// 设置键盘焦点 setFocusableInTouchMode(true);// 设置触摸屏焦点 } protected
void paintView(Canvas canvas) { // 自定义方法，类似于onDraw }public
void rePaint() { // 自定义类似于invalidate方法，调用此方法刷新View Canvas c = null; try
{ c = holder.lockCanvas(); paintView(c); } finally
{ if
(c != null) { holder.unlockCanvasAndPost(c); } } } @Override public
void surfaceCreated(SurfaceHolder holder) { Canvas canvas = holder.lockCanvas(null);// 获取画布 canvas.drawColor(Color.WHITE);// 设置画布背景 holder.unlockCanvasAndPost(canvas);// 解锁画布，提交画好的图像 } @Override public
void surfaceChanged(SurfaceHolder holder, int
format, int
width, int
height) { } @Override public
void surfaceDestroyed(SurfaceHolder holder) { }} |
2.Invalidate和postinvalidate
Invalidate()必须是在UI线程中被调用，如果在新线程中更新视图的就调用postInvalidate()。
3.view.invalidate 调用过程
父View负责刷新、布局显示子View；而当子View需要刷新时，则是通知父View来完成。
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void invalidate(boolean
invalidateCache) { 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); } } } |
子View调用invalidate时，首先找到自己父View(View的成员变量mParent记录自己的父View)，然后将AttachInfo中保存的信息告诉父View刷新自己。
View的父子关系的建立分为两种情况：
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; } .....} |
2)DecorView注册给WindowManagerImpl时，产生一个ViewRoot作为其父View。
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public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView){ ..... view.assignParent(this); ....} |
AttachInfo是在View第一次attach到Window时，ViewRoot传给自己的子View的。这个AttachInfo之后，会顺着布局体系一直传递到最底层的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); }} |
并且在新的View被加入ViewGroup时，也会将该AttachInfo传给加入的View
ViewGroup.java
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private
void addViewInner(View child, int
index, LayoutParams params, boolean
preventRequestLayout) { child.dispatchAttachedToWindow(mAttachInfo, (mViewFlags&VISIBILITY_MASK));} |
到这里明白了mParent与AttachInfo代表的意义，可以继续刷新过程的分析。
在invalidate中，调用父View的invalidateChild，这是一个从第向上回溯的过程，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。
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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) { // 根据父View的位置，偏移刷新区域 dirty.offset(location[CHILD_LEFT_INDEX] - mScrollX, location[CHILD_TOP_INDEX] - mScrollY); final
int left = mLeft; final
int top = mTop; //计算实际可刷新区域 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;} |
这个向上回溯的过程直到ViewRoot那里结束，由ViewRoot对这个最终的刷新区域做刷新。
ViewRoot.java
public void invalidateChild(View child, Rect dirty) { scheduleTraversals(); }
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