View体系的一些小问题|青训营笔记

//View
public <T extends View> T findViewById(@IdRes int id) {
    if(id == NO_ID){
        return Null;
    }
    return findViewTraversal(id);
}
public <T extends View> T findViewTraversal(@IdRes int id) {
    if(id == mID){
        return (T)this;
    }
    return null;
}
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//ViewGroup
/**
     * {@hide}
     */
    @Override
    protected <T extends View> T findViewTraversal(@IdRes int id) {
        if (id == mID) {
            return (T) this;
        }
        final View[] where = mChildren;
        final int len = mChildrenCount;
        for (int i = 0; i < len; i++) {
            View v = where[i];
            if ((v.mPrivateFlags & PFLAG_IS_ROOT_NAMESPACE) == 0) {
                v = v.findViewById(id);
                if (v != null) {
                    return (T) v;
                }
            }
        }
        return null;
    }
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//View 
public boolean onTouchEvent(MotionEvent event) {
        ...
        if (clickable || (viewFlags & TOOLTIP) == TOOLTIP) {
            switch (action) {
                case MotionEvent.ACTION_UP:
                    mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;
                    ...
                    if ((mPrivateFlags & PFLAG_PRESSED) != 0 || prepressed) {
                        ...
                            if (!mHasPerformedLongPress && !mIgnoreNextUpEvent) {
                            // This is a tap, so remove the longpress check
                            removeLongPressCallback();//标注2
                            // Only perform take click actions if we were in the pressed state
                            if (!focusTaken) {
                                // Use a Runnable and post this rather than calling
                                // performClick directly. This lets other visual state
                                // of the view update before click actions start.
                                if (mPerformClick == null) {
                                    mPerformClick = new PerformClick();//标注1
                                }
                                if (!post(mPerformClick)) {
                                    performClickInternal();
                                }
                            }
                        ...
                    mIgnoreNextUpEvent = false;
                    break;
                case MotionEvent.ACTION_DOWN:
                    ...
                    if (!clickable) {
                        checkForLongClick(//标注3
                                ViewConfiguration.getLongPressTimeout(),
                                x,
                                y,
                                TOUCH_GESTURE_CLASSIFIED__CLASSIFICATION__LONG_PRESS);
                        break;
                    }
                    ...
                    break;
                ...
            }
            return true;
        }
        return false;
    }
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