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();
}