博客

在Android源码中,包括一些比较规范的源码中,通常会出现flag(我理解我标志位)。

可以这么认为:

 void setFlags(int flags, int mask) {
        int old = mViewFlags;//将标记赋值给old
        mViewFlags = (mViewFlags & ~mask) | (flags & mask);//mViewFlags清除mask后添加从flags中取出的mask标志

        int changed = mViewFlags ^ old;//取出新旧标记的不同部分。
        if (changed == 0) {
            return;
        }
        int privateFlags = mPrivateFlags;

        /* Check if the FOCUSABLE bit has changed */
        if (((changed & FOCUSABLE_MASK) != 0) &&
                ((privateFlags & PFLAG_HAS_BOUNDS) !=0)) {
            if (((old & FOCUSABLE_MASK) == FOCUSABLE)
                    && ((privateFlags & PFLAG_FOCUSED) != 0)) {
                /* Give up focus if we are no longer focusable */
                clearFocus();
            } else if (((old & FOCUSABLE_MASK) == NOT_FOCUSABLE)
                    && ((privateFlags & PFLAG_FOCUSED) == 0)) {
                /*
                 * Tell the view system that we are now available to take focus
                 * if no one else already has it.
                 */
                if (mParent != null) mParent.focusableViewAvailable(this);
            }
            if (AccessibilityManager.getInstance(mContext).isEnabled()) {
                notifyAccessibilityStateChanged();
            }
        }

        if ((flags & VISIBILITY_MASK) == VISIBLE) {
            if ((changed & VISIBILITY_MASK) != 0) {
                /*
                 * If this view is becoming visible, invalidate it in case it changed while
                 * it was not visible. Marking it drawn ensures that the invalidation will
                 * go through.
                 */
                mPrivateFlags |= PFLAG_DRAWN;
                invalidate(true);

                needGlobalAttributesUpdate(true);

                // a view becoming visible is worth notifying the parent
                // about in case nothing has focus.  even if this specific view
                // isn't focusable, it may contain something that is, so let
                // the root view try to give this focus if nothing else does.
                if ((mParent != null) && (mBottom > mTop) && (mRight > mLeft)) {
                    mParent.focusableViewAvailable(this);
                }
            }
        }

        /* 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) && hasFocus()) {
                // root view becoming invisible shouldn't clear focus and accessibility focus
                if (getRootView() != this) {
                    clearFocus();
                    clearAccessibilityFocus();
                }
            }
            if (mAttachInfo != null) {
                mAttachInfo.mViewVisibilityChanged = true;
            }
        }

        if ((changed & VISIBILITY_MASK) != 0) {
            if (mParent instanceof ViewGroup) {
                ((ViewGroup) mParent).onChildVisibilityChanged(this,
                        (changed & VISIBILITY_MASK), (flags & VISIBILITY_MASK));
                ((View) mParent).invalidate(true);
            } else if (mParent != null) {
                mParent.invalidateChild(this, null);
            }
            dispatchVisibilityChanged(this, (flags & VISIBILITY_MASK));
        }

        if ((changed & WILL_NOT_CACHE_DRAWING) != 0) {
            destroyDrawingCache();
        }

        if ((changed & DRAWING_CACHE_ENABLED) != 0) {
            destroyDrawingCache();
            mPrivateFlags &= ~PFLAG_DRAWING_CACHE_VALID;
            invalidateParentCaches();
        }

        if ((changed & DRAWING_CACHE_QUALITY_MASK) != 0) {
            destroyDrawingCache();
            mPrivateFlags &= ~PFLAG_DRAWING_CACHE_VALID;
        }

        if ((changed & DRAW_MASK) != 0) {
            if ((mViewFlags & WILL_NOT_DRAW) != 0) {
                if (mBackground != null) {
                    mPrivateFlags &= ~PFLAG_SKIP_DRAW;
                    mPrivateFlags |= PFLAG_ONLY_DRAWS_BACKGROUND;
                } else {
                    mPrivateFlags |= PFLAG_SKIP_DRAW;
                }
            } else {
                mPrivateFlags &= ~PFLAG_SKIP_DRAW;
            }
            requestLayout();
            invalidate(true);
        }

        if ((changed & KEEP_SCREEN_ON) != 0) {
            if (mParent != null && mAttachInfo != null && !mAttachInfo.mRecomputeGlobalAttributes) {
                mParent.recomputeViewAttributes(this);
            }
        }

        if (AccessibilityManager.getInstance(mContext).isEnabled()
                && ((changed & FOCUSABLE) != 0 || (changed & CLICKABLE) != 0
                        || (changed & LONG_CLICKABLE) != 0 || (changed & ENABLED) != 0)) {
            notifyAccessibilityStateChanged();
        }
    }