android中View的GONE和INVISIBLE的原理

 /* Check if the GONE bit has changed */
        if ((changed & GONE) != 0) {
            needGlobalAttributesUpdate(false);
            requestLayout();

            if (((mViewFlags & VISIBILITY_MASK) == GONE)) {
                if (hasFocus()) clearFocus();
                clearAccessibilityFocus();
                destroyDrawingCache();
                if (mParent instanceof View) {
                    // GONE views noop invalidation, so invalidate the parent
                    ((View) mParent).invalidate(true);
                }
                // Mark the view drawn to ensure that it gets invalidated properly the next
                // time it is visible and gets invalidated
                mPrivateFlags |= PFLAG_DRAWN;
            }
            if (mAttachInfo != null) {
                mAttachInfo.mViewVisibilityChanged = true;
            }
        }

        /* Check if the VISIBLE bit has changed */
        if ((changed & INVISIBLE) != 0) {
            needGlobalAttributesUpdate(false);
            /*
             * If this view is becoming invisible, set the DRAWN flag so that
             * the next invalidate() will not be skipped.
             */
            mPrivateFlags |= PFLAG_DRAWN;

            if (((mViewFlags & VISIBILITY_MASK) == INVISIBLE)) {
                // root view becoming invisible shouldn‘t clear focus and accessibility focus
                if (getRootView() != this) {
                    if (hasFocus()) clearFocus();
                    clearAccessibilityFocus();
                }
            }
            if (mAttachInfo != null) {
                mAttachInfo.mViewVisibilityChanged = true;
            }
        }