在Android的佈局體系中，父View負責重新整理、佈局顯示子View；而當子View需要重新整理時，則是通知父View來完成。這種處理邏輯在View的程式碼中明確的表現出來：

  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呼叫invalidate時，首先找到自己父View(View的成員變數mParent記錄自己的父View)，然後將AttachInfo中儲存的資訊告訴父View重新整理自己。

View的父子關係的建立分為兩種情況：

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註冊給WindowManagerImpl時，產生一個ViewRoot作為其父View。

public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView){
    .....
    view.assignParent(this);
    ....
}

AttachInfo是在View第一次attach到Window時，ViewRoot傳給自己的子View的。這個AttachInfo之後，會順著佈局體系一直傳遞到最底層的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);
    }
}

並且在新的View被加入ViewGroup時，也會將該AttachInfo傳給加入的View

ViewGroup.java

private void addViewInner(View child, int index, LayoutParams params, boolean preventRequestLayout) {
    child.dispatchAttachedToWindow(mAttachInfo, (mViewFlags&VISIBILITY_MASK));
}

到這裡明白了mParent與AttachInfo代表的意義，可以繼續重新整理過程的分析。

在invalidate中，呼叫父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重新整理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;
        // 需要重新整理的子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，偏移重新整理區域 
            dirty.offset(location[CHILD_LEFT_INDEX] - mScrollX, location[CHILD_TOP_INDEX] - mScrollY);

            final int left = mLeft;
            final int top = mTop;
            //計算實際可重新整理區域 
            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那裡結束，由ViewRoot對這個最終的重新整理區域做重新整理。

ViewRoot.java

public void invalidateChild(View child, Rect dirty) {
    scheduleTraversals();
}

另外：

Invalidate()方法不能放線上程中，所以需要把Invalidate()方法放在Handler中。在MyThread中只需要在規定時間內傳送一個Message給handler，當Handler接收到訊息就呼叫Invalidate()方法。

postInvalidate()方法就可以放線上程中做處理，就不需要Handler。

而上面的新執行緒MyThread可以放在OnCreate()中開始，也可以放在OnStart()中開始。

Invalidate()方法和postInvalidate()都可以在主執行緒中呼叫而重新整理檢視。

Invalidate()方法在SDK中是這樣描述的：Invalidatethe whole view. If the view is visible, onDraw(Canvas) will be called at somepoint in the future. This must be called from a UI thread. To call from anon-UI thread, call postInvalidate().  當Invalidate()被呼叫的時候，View的OnDraw()就會被呼叫，Invalidate()必須是在UI執行緒中被呼叫，如果在新執行緒中更新檢視的就呼叫postInvalidate()。