android中调用requestFocus()的详细过程

view中

 public boolean requestFocus(int direction, Rect previouslyFocusedRect) {        return requestFocusNoSearch(direction, previouslyFocusedRect); } private boolean requestFocusNoSearch(int direction, Rect previouslyFocusedRect) {     // need to be focusable        if ((mViewFlags & FOCUSABLE_MASK) != FOCUSABLE ||                (mViewFlags & VISIBILITY_MASK) != VISIBLE) {            return false;        }        // need to be focusable in touch mode if in touch mode        if (isInTouchMode() &&            (FOCUSABLE_IN_TOUCH_MODE != (mViewFlags & FOCUSABLE_IN_TOUCH_MODE))) {               return false;        }        // need to not have any parents blocking us        if (hasAncestorThatBlocksDescendantFocus()) {//判断父视图是否阻止子视图获得焦点            return false;        }        handleFocusGainInternal(direction, previouslyFocusedRect);//进行具体的焦点获取        return true; }

void handleFocusGainInternal(int direction, Rect previouslyFocusedRect) {        if (DBG) {            System.out.println(this + " requestFocus()");        }        if ((mPrivateFlags & FOCUSED) == 0) {            mPrivateFlags |= FOCUSED;            if (mParent != null) {                mParent.requestChildFocus(this, this);//第一个参数是child视图，第二个是focused视图，该函数内部进行递归调用            }//注意时态，xxxed()和xxx()的区别是，前者是执行完之后回调，后者是在执行前回调            onFocusChanged(true, direction, previouslyFocusedRect);            refreshDrawableState();            if (AccessibilityManager.getInstance(mContext).isEnabled()) {                notifyAccessibilityStateChanged();            }        }}

一般来说，父视图是ViewGroup，requestChildFocus在ViewGroup中的实现

public void requestChildFocus(View child, View focused) {        if (DBG) {            System.out.println(this + " requestChildFocus()");        }        if (getDescendantFocusability() == FOCUS_BLOCK_DESCENDANTS) {            return;        }        // Unfocus us, if necessary        super.unFocus();        // We had a previous notion of who had focus. Clear it.        if (mFocused != child) {            if (mFocused != null) {                mFocused.unFocus();            }            mFocused = child;        }        if (mParent != null) {            mParent.requestChildFocus(this, focused);//最终会递归到ViewRoot中的equestChildFocus        }}

ViewRoot中的requestChildFocus

public void requestChildFocus(View child, View focused) {        checkThread();//确保在UI线程中        if (mFocusedView != focused) {//其实ViewGroup中已经检查过，mFocusedView一定不是目标焦点视图            mAttachInfo.mTreeObserver.dispatchOnGlobalFocusChange(mFocusedView, focused);            scheduleTraversals();//发起View遍历请求        }        mFocusedView = mRealFocusedView = focused;        if (DEBUG_INPUT_RESIZE) Log.v(TAG, "Request child focus: focus now "                + mFocusedView);

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