Android View 的刷新機制

今天學習android VIEW的刷新機制，之前一直以為是調用VIEW的刷新就自己調用刷新函數。今天學習了一下view的刷新機制，還是表示學習到很多的知識啊。

 

感想就是自己要多閱讀android的源代碼，其實很多的消息傳遞等等的機制，都是通過閱讀android的源代碼得到的，所以有事沒事就去看源代碼玩吧~

 

好了，來到正題，關鍵的一句話就是：

 

在Android的布局體系中，父View負責刷新、布局顯示子View；而當子View需要刷新時，則是通知父View來完成。

 

步驟就是：

1、調用子View的invalidate（）

2、跳轉到上一層的invalidateChild函數中區

3、在一次調用invalidateChildInParent的函數一次層層刷新

4、具體的刷新後續操作，我就不清楚了，調用invalidate最終在代碼上就在invalidateChild終止了的，所以表示有點點不清晰，求各位大牛介紹一下吧。。。。。？在此謝過了。。

 

讓我來閱讀源代碼：

首先在View類中：

 

    /**
     * Invalidate the whole view. If the view is visible, {@link #onDraw} will
     * be called at some point in the future. This must be called from a
     * UI thread. To call from a non-UI thread, call {@link #postInvalidate()}.
     */
    public void invalidate() {
        if (ViewDebug.TRACE_HIERARCHY) {
            ViewDebug.trace(this, ViewDebug.HierarchyTraceType.INVALIDATE);
        }

        if ((mPrivateFlags & (DRAWN | HAS_BOUNDS)) == (DRAWN | HAS_BOUNDS)) {
            mPrivateFlags &= ~DRAWN & ~DRAWING_CACHE_VALID;

            final ViewParent p = mParent; //獲得父類View的對象
            final AttachInfo ai = mAttachInfo;//獲得匹配
            if (p != null && ai != null) {
                final Rect r = ai.mTmpInvalRect;  
                r.set(0, 0, mRight - mLeft, mBottom - mTop);//設置本View的尺寸，其實就是大小沒有設置位置

                // Don't call invalidate -- we don't want to internally scroll
                // our own bounds
                p.invalidateChild(this, r);  //調用父類的刷新函數
            }
        }
    }

 

 

下面我們來到Viewgroup對象：

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。

 /**
     * Don't call or override this method. It is used for the implementation of
     * the view hierarchy.
     */
    public final void invalidateChild(View child, final Rect dirty) {
        if (ViewDebug.TRACE_HIERARCHY) {
            ViewDebug.trace(this, ViewDebug.HierarchyTraceType.INVALIDATE_CHILD);
        }

        ViewParent parent = this;
        final AttachInfo attachInfo = mAttachInfo;
        if (attachInfo != null) {
            final int[] location = attachInfo.mInvalidateChildLocation;

            // 刷新子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);
        }
   

 

  /**
     * Don't call or override this method. It is used for the implementation of
     * the view hierarchy.
     *
     * This implementation returns null if this ViewGroup does not have a parent,
     * if this ViewGroup is already fully invalidated or if the dirty rectangle
     * does not intersect with this ViewGroup's bounds.
     */    www.2cto.com
    public ViewParent invalidateChildInParent(final int[] location, final Rect dirty) {
        if (ViewDebug.TRACE_HIERARCHY) {
            ViewDebug.trace(this, ViewDebug.HierarchyTraceType.INVALIDATE_CHILD_IN_PARENT);
        }

        if ((mPrivateFlags & DRAWN) == DRAWN) {
            if ((mGroupFlags & (FLAG_OPTIMIZE_INVALIDATE | FLAG_ANIMATION_DONE)) !=
                        FLAG_OPTIMIZE_INVALIDATE) {

               // 由父類的的位置，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;

                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;
    }

 

另外：

  Invalidate()方法不能放在線程中，所以需要把Invalidate()方法放在Handler中。在MyThread中只需要在規定時間內發送一個Message給handler，當Handler接收到消息就調用Invalidate()方法。

    postInvalidate()方法就可以放在線程中做處理，就不需要Handler。

    而上面的新線程MyThre可以放在OnCreate()中開始，也可以放在OnStart()中開始。

    Invalidate()方法和postInvalidate()都可以在主線程中調用而刷新視圖。

    Invalidate()方法在SDK中是這樣描述的：Invalidate the whole view. If the view is visible, onDraw(Canvas) will be called at some point in the future. This must be called from a UI thread. To call from a non-UI thread, call postInvalidate().  當Invalidate()被調用的時候，View的OnDraw()就會被調用，Invalidate()必須是在UI線程中被調用，如果在新線程中更新視圖的就調用postInvalidate()。

 

作者：ljz2009y