绪论
在上一篇中，大概说明了下WindowInsets的概念和分发逻辑，然而在部分情况下，我们会发现即便设置了fitSSystemWindows = true 也并没有生效；而且从上文已知的情况可以看出，即便消费WindowInsets似乎也只是在消费SystemWindowInsets，其它的Insets似乎并没有被消耗。这一篇将解决这两个问题。
mWindowDecorInsets和mStableInsets的消耗
fitSSystemWindows = true 生效的首要条件
这个问题的答案，我们可以在ViewRootImpl和Decoreview这两个类中找到答案
在ViewRootImpl的源码中，我们可以发现这样一段代码
private void performTraversals() {
...
...
dispatchApplyInsets(host);
...
...
}
void dispatchApplyInsets(View host) {
host.dispatchApplyWindowInsets(getWindowInsets(true /* forceConstruct */));
}
WindowInsets getWindowInsets(boolean forceConstruct) {
if (mLastWindowInsets == null || forceConstruct) {
mDispatchContentInsets.set(mAttachInfo.mContentInsets);
mDispatchStableInsets.set(mAttachInfo.mStableInsets);
Rect contentInsets = mDispatchContentInsets;
Rect stableInsets = mDispatchStableInsets;
// For dispatch we preserve old logic, but for direct requests from Views we allow to
// immediately use pending insets.
if (!forceConstruct
&& (!mPendingContentInsets.equals(contentInsets) ||
!mPendingStableInsets.equals(stableInsets))) {
contentInsets = mPendingContentInsets;
stableInsets = mPendingStableInsets;
}
Rect outsets = mAttachInfo.mOutsets;
if (outsets.left > 0 || outsets.top > 0 || outsets.right > 0 || outsets.bottom > 0) {
contentInsets = new Rect(contentInsets.left + outsets.left,
contentInsets.top + outsets.top, contentInsets.right + outsets.right,
contentInsets.bottom + outsets.bottom);
}
mLastWindowInsets = new WindowInsets(contentInsets,
null /* windowDecorInsets */, stableInsets,
mContext.getResources().getConfiguration().isScreenRound(),
mAttachInfo.mAlwaysConsumeNavBar);
}
return mLastWindowInsets;
}
从上述代码中，可以发现被dispatchapply的WindowInsets来源于getWindowInsets(...)。而在这个函数中，我们可以发现mWindowDecorInsets值为null，表明其从一开始就是消耗状态。
再看看DecoreView的代码
@Override
public WindowInsets onApplyWindowInsets(WindowInsets insets) {
...
...
insets = updateColorViews(insets, true /* animate */);
insets = updateStatusGuard(insets);
insets = updateNavigationGuard(insets);
if (getForeground() != null) {
drawableChanged();
}
return insets;
}
WindowInsets updateColorViews(WindowInsets insets, boolean animate) {
WindowManager.LayoutParams attrs = mWindow.getAttributes();
int sysUiVisibility = attrs.systemUiVisibility | getWindowSystemUiVisibility();
...
...
boolean consumingNavBar =
(attrs.flags & FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDS) != 0
&& (sysUiVisibility & SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION) == 0
&& (sysUiVisibility & SYSTEM_UI_FLAG_HIDE_NAVIGATION) == 0
|| mLastShouldAlwaysConsumeNavBar;
// If we didn't request fullscreen layout, but we still got it because of the
// mForceWindowDrawsStatusBarBackground flag, also consume top inset.
boolean consumingStatusBar = (sysUiVisibility & SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN) == 0
&& (sysUiVisibility & FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDS) == 0
&& (attrs.flags & FLAG_LAYOUT_IN_SCREEN) == 0
&& (attrs.flags & FLAG_LAYOUT_INSET_DECOR) == 0
&& mForceWindowDrawsStatusBarBackground
&& mLastTopInset != 0;
int consumedTop = consumingStatusBar ? mLastTopInset : 0;
int consumedRight = consumingNavBar ? mLastRightInset : 0;
int consumedBottom = consumingNavBar ? mLastBottomInset : 0;
int consumedLeft = consumingNavBar ? mLastLeftInset : 0;
if (mContentRoot != null
&& mContentRoot.getLayoutParams() instanceof MarginLayoutParams){
MarginLayoutParams lp = (MarginLayoutParams) mContentRoot.getLayoutParams();
if (lp.topMargin != consumedTop || lp.rightMargin != consumedRight
|| lp.bottomMargin != consumedBottom || lp.leftMargin != consumedLeft) {
lp.topMargin = consumedTop;
lp.rightMargin = consumedRight;
lp.bottomMargin = consumedBottom;
lp.leftMargin = consumedLeft;
mContentRoot.setLayoutParams(lp);
if (insets == null) {
// The insets have changed, but we're not currently in the process
// of dispatching them.
requestApplyInsets();
}
}
if (insets != null) {
insets = insets.replaceSystemWindowInsets(
insets.getSystemWindowInsetLeft() - consumedLeft,
insets.getSystemWindowInsetTop() - consumedTop,
insets.getSystemWindowInsetRight() - consumedRight,
insets.getSystemWindowInsetBottom() - consumedBottom);
}
}
if (insets != null) {
insets = insets.consumeStableInsets();
}
return insets;
}
从上述代码中，我们可以发现在没设置 SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION 和 SYSTEM_UI_FLAG_HIDE_NAVIGATION这两个属性时，会通过设置margin的方式消耗掉底部和左部mSystemWindowInsets的底部，而没设置 SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN 则会消费掉mSystemWindowInsets的顶部和右部。并且在insets不为空的情况下一定会消耗掉mStableInsets。这同时也是另外一个问题的答案，要想fitsSystemWindows起效，先得设置合适的sysUiVisibility属性。
部分特殊View的 WindowInsets分发逻辑
- DrawerLayout
public DrawerLayout(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
...
...
if (ViewCompat.getFitsSystemWindows(this)) {
IMPL.configureApplyInsets(this);
mStatusBarBackground = IMPL.getDefaultStatusBarBackground(context);
}
...
...
}
WindowInsets的分发将通过IMPL.configureApplyInsets(this)实现，以android 版本大于20为例
public void configureApplyInsets(View drawerLayout) {
DrawerLayoutCompatApi21.configureApplyInsets(drawerLayout);
}
public static void configureApplyInsets(View drawerLayout) {
if (drawerLayout instanceof DrawerLayoutImpl) {
drawerLayout.setOnApplyWindowInsetsListener(new InsetsListener());
drawerLayout.setSystemUiVisibility(View.SYSTEM_UI_FLAG_LAYOUT_STABLE
| View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN);
}
}
在该函数中设置了OnApplyWindowInsetsListener，并设置了View.SYSTEM_UI_FLAG_LAYOUT_STABLE和 View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN两个属性，根据上文可以判断，Decoreview将不会消耗mSysWindowInsets的顶部，它会参与向下级的View分发，再看看InsetsListenr的实现。
static class InsetsListener implements View.OnApplyWindowInsetsListener {
@Override
public WindowInsets onApplyWindowInsets(View v, WindowInsets insets) {
final DrawerLayoutImpl drawerLayout = (DrawerLayoutImpl) v;
drawerLayout.setChildInsets(insets, insets.getSystemWindowInsetTop() > 0);
return insets.consumeSystemWindowInsets();
}
}
DrawerLayout将会消耗mSystemWindowInsets。
再看下setChildInsets实现,代码实现在DrawerLayout类中
@Override
public void setChildInsets(Object insets, boolean draw) {
mLastInsets = insets;
mDrawStatusBarBackground = draw;
setWillNotDraw(!draw && getBackground() == null);
requestLayout();
}
可以看出mLastInsets将会参与mSystemWindowInsets的后续处理
在onMeasure(...) 函数中可以发现
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
if (applyInsets) {
final int cgrav = GravityCompat.getAbsoluteGravity(lp.gravity, layoutDirection);
if (ViewCompat.getFitsSystemWindows(child)) {
IMPL.dispatchChildInsets(child, mLastInsets, cgrav);
} else {
IMPL.applyMarginInsets(lp, mLastInsets, cgrav);
}
}
}
//DrawerLayoutCompatApi21.java
public static void dispatchChildInsets(View child, Object insets, int gravity) {
WindowInsets wi = (WindowInsets) insets;
if (gravity == Gravity.LEFT) {
wi = wi.replaceSystemWindowInsets(wi.getSystemWindowInsetLeft(),
wi.getSystemWindowInsetTop(), 0, wi.getSystemWindowInsetBottom());
} else if (gravity == Gravity.RIGHT) {
wi = wi.replaceSystemWindowInsets(0, wi.getSystemWindowInsetTop(),
wi.getSystemWindowInsetRight(), wi.getSystemWindowInsetBottom());
}
child.dispatchApplyWindowInsets(wi);
}
public static void applyMarginInsets(ViewGroup.MarginLayoutParams lp, Object insets,int gravity) {
WindowInsets wi = (WindowInsets) insets;
if (gravity == Gravity.LEFT) {
wi = wi.replaceSystemWindowInsets(wi.getSystemWindowInsetLeft(),
wi.getSystemWindowInsetTop(), 0, wi.getSystemWindowInsetBottom());
} else if (gravity == Gravity.RIGHT) {
wi = wi.replaceSystemWindowInsets(0, wi.getSystemWindowInsetTop(),
wi.getSystemWindowInsetRight(), wi.getSystemWindowInsetBottom());
}
lp.leftMargin = wi.getSystemWindowInsetLeft();
lp.topMargin = wi.getSystemWindowInsetTop();
lp.rightMargin = wi.getSystemWindowInsetRight();
lp.bottomMargin = wi.getSystemWindowInsetBottom();
}
如果child中设置fitsSystemWindow = true 属性，则会执行子view的dispatch, 否则会重新设置View的margin属性
- CoordinatorLayout
与DrawerLayout类似，通过设置OnApplyWindowInsetsListener来改变它的dispatchApply逻辑，与DrawerLayout最大的区别在于它对子view的分发是通过Behavior实现的。
- CollapsingToolbarLayout
它也是通过设置OnApplyWindowInsetsListener来实现的， 并且当它的VieParent是AppBarLayout时，它的fitsSystemWindow属性与其ViewParent一致
@Override
protected void onAttachedToWindow() {
super.onAttachedToWindow();
// Add an OnOffsetChangedListener if possible
final ViewParent parent = getParent();
if (parent instanceof AppBarLayout) {
// Copy over from the ABL whether we should fit system windows
ViewCompat.setFitsSystemWindows(this, ViewCompat.getFitsSystemWindows((View) parent));
if (mOnOffsetChangedListener == null) {
mOnOffsetChangedListener = new OffsetUpdateListener();
}
((AppBarLayout) parent).addOnOffsetChangedListener(mOnOffsetChangedListener);
// We're attached, so lets request an inset dispatch
ViewCompat.requestApplyInsets(this);
}
}
WindowInsetsCompat onWindowInsetChanged(final WindowInsetsCompat insets) {
WindowInsetsCompat newInsets = null;
if (ViewCompat.getFitsSystemWindows(this)) {
// If we're set to fit system windows, keep the insets
newInsets = insets;
}
// If our insets have changed, keep them and invalidate the scroll ranges...
if (!objectEquals(mLastInsets, newInsets)) {
mLastInsets = newInsets;
requestLayout();
}
// Consume the insets. This is done so that child views with fitSystemWindows=true do not
// get the default padding functionality from View
return insets.consumeSystemWindowInsets();
}
它会消耗windowinsets并且让子view不再消耗WindowInsets了。
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