Android view 刷新流程
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）
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。
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
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。
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
void dispatchAttachedToWindow(AttachInfo info, int visibility) {
mAttachInfo = info;
.....
}
ViewGroup.java
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
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。
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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