从源码角度探究fitSystemWindows属性。
从Android 4.4开始,Android系统加入了一个比较酷的功能,就是我们可以设置状态栏的的颜色了,有个这个功能,状态栏就不再是黑乎乎的了,我们就可以根据我们应用的主色去设置状态栏的颜色,使得应用体验变得好一些,所以我们通过如下方式设置状态栏透明。
1 | window.setFlags(WindowManager.LayoutParams.FLAG_TRANSLUCENT_STATUS, WindowManager.LayoutParams.FLAG_TRANSLUCENT_STATUS); window.setFlags(WindowManager.LayoutParams.FLAG_TRANSLUCENT_NAVIGATION, WindowManager.LayoutParams.FLAG_TRANSLUCENT_NAVIGATION); |
但是设置了状态栏和导航栏透明之后,发现Activity的contentView超出了ActionBar,那么我们就要使用fitSystemWindws来解决这个问题,关于具体如何解决这个问题,在Android4.4新的特性,在应用内开启透明状态栏和透明虚拟按钮这篇博客中有详细介绍。
那么android:fitSystemWindows到底是什么东西啊,它是怎样计算的?
在Android Framework的源代码中查看View.java,有这几个重要方法,如下:
- dispatchApplyWindowInsets
- onApplyWindowInsets
- fitSystemWindows
是一个自定义的View,并且覆盖View的这三个方法,打印出Log,可以发现这三个方法的调用顺序是
- dispatchApplyWindowInsets
- onApplyWindowInsets
- fitSystemWindows
这里我们通过代码调试的方法来查看Android Framework的方法调用堆栈,如图:
根据堆栈可以发现,dispatchApplyWindowInsets方法是在ViewRootImpl.performMeasure(int,int)方法中调用的。也就是说,dispatchApplyWindowInsets是在整个View Hierarchy的measure过程中调用的。
在从layout文件中解释到fitSystemWindows为true设置标志位。那这个标志为在什么时候起的作用。1
case com.android.internal.R.styleable.View_fitsSystemWindows:
if (a.getBoolean(attr, false)) {
viewFlagValues |= FITS_SYSTEM_WINDOWS;
viewFlagMasks |= FITS_SYSTEM_WINDOWS;
}
break;
再看上面那幅堆栈图,在ActionBarOverlayLayout.measure()中开始调用fitSystemWindows的相关方法,进入ActionBarOverlayLayout的源码。
1 | protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { //通过findViewById方法,得到布局文件中的view pullChildren(); int maxHeight = 0; int maxWidth = 0; int childState = 0; int topInset = 0; int bottomInset = 0; //测量ActionBar的高度和宽度 measureChildWithMargins(mActionBarTop, widthMeasureSpec, 0, heightMeasureSpec, 0); LayoutParams lp = (LayoutParams) mActionBarTop.getLayoutParams(); maxWidth = Math.max(maxWidth, mActionBarTop.getMeasuredWidth() + lp.leftMargin + lp.rightMargin); maxHeight = Math.max(maxHeight, mActionBarTop.getMeasuredHeight() + lp.topMargin + lp.bottomMargin); childState = ViewUtils.combineMeasuredStates(childState, ViewCompat.getMeasuredState(mActionBarTop)); // xlarge screen layout doesn't have bottom action bar. //测量ActionBar底部区域的高度和宽度 if (mActionBarBottom != null) { measureChildWithMargins(mActionBarBottom, widthMeasureSpec, 0, heightMeasureSpec, 0); lp = (LayoutParams) mActionBarBottom.getLayoutParams(); maxWidth = Math.max(maxWidth, mActionBarBottom.getMeasuredWidth() + lp.leftMargin + lp.rightMargin); maxHeight = Math.max(maxHeight, mActionBarBottom.getMeasuredHeight() + lp.topMargin + lp.bottomMargin); childState = ViewUtils.combineMeasuredStates(childState, ViewCompat.getMeasuredState(mActionBarBottom)); } final int vis = ViewCompat.getWindowSystemUiVisibility(this); final boolean stable = (vis & SYSTEM_UI_FLAG_LAYOUT_STABLE) != 0; if (stable) { // This is the standard space needed for the action bar. For stable measurement, // we can't depend on the size currently reported by it -- this must remain constant. topInset = mActionBarHeight; //考虑到ActionbarTab的高度,计算topInset if (mHasNonEmbeddedTabs) { final View tabs = mActionBarTop.getTabContainer(); if (tabs != null) { // If tabs are not embedded, increase space on top to account for them. topInset += mActionBarHeight; } } } else if (mActionBarTop.getVisibility() != GONE) { // This is the space needed on top of the window for all of the action bar // and tabs. topInset = mActionBarTop.getMeasuredHeight(); } //如果ActionBar是split模式,考虑底部的高度,计算insetBottom if (mDecorToolbar.isSplit()) { // If action bar is split, adjust bottom insets for it. if (mActionBarBottom != null) { if (stable) { bottomInset = mActionBarHeight; } else { bottomInset = mActionBarBottom.getMeasuredHeight(); } } } // If the window has not requested system UI layout flags, we need to // make sure its content is not being covered by system UI... though it // will still be covered by the action bar if they have requested it to // overlay. mContentInsets.set(mBaseContentInsets); mInnerInsets.set(mBaseInnerInsets); if (!mOverlayMode && !stable) { mContentInsets.top += topInset; mContentInsets.bottom += bottomInset; } else { mInnerInsets.top += topInset; mInnerInsets.bottom += bottomInset; } //在ActionBar为非Overlay模式下,应用计算好的ContentInsets applyInsets(mContent, mContentInsets, true, true, true, true); // if (!mLastInnerInsets.equals(mInnerInsets)) { // If the inner insets have changed, we need to dispatch this down to // the app's fitSystemWindows(). We do this before measuring the content // view to keep the same semantics as the normal fitSystemWindows() call. mLastInnerInsets.set(mInnerInsets); //Overlay模式下,将InnerInsets分发到子View中。 mContent.dispatchFitSystemWindows(mInnerInsets); } measureChildWithMargins(mContent, widthMeasureSpec, 0, heightMeasureSpec, 0); lp = (LayoutParams) mContent.getLayoutParams(); maxWidth = Math.max(maxWidth, mContent.getMeasuredWidth() + lp.leftMargin + lp.rightMargin); maxHeight = Math.max(maxHeight, mContent.getMeasuredHeight() + lp.topMargin + lp.bottomMargin); childState = ViewUtils.combineMeasuredStates(childState, ViewCompat.getMeasuredState(mContent)); // Account for padding too maxWidth += getPaddingLeft() + getPaddingRight(); maxHeight += getPaddingTop() + getPaddingBottom(); // Check against our minimum height and width maxHeight = Math.max(maxHeight, getSuggestedMinimumHeight()); maxWidth = Math.max(maxWidth, getSuggestedMinimumWidth()); setMeasuredDimension( ViewCompat.resolveSizeAndState(maxWidth, widthMeasureSpec, childState), ViewCompat.resolveSizeAndState(maxHeight, heightMeasureSpec, childState << MEASURED_HEIGHT_STATE_SHIFT)); } |
根据上面的堆栈图知道mContent是NativeActionModeAwareLayout类型,而NativeActionModeAwareLayout,没有dispatchFitSystemWindows方法,那么查看其父类的dispatchFitSystemWindows方法。NativeActionModeAwareLayout的父类是ContentFrameLayout类型,看它的dispatchFitSystemWindows方法。
1 | public void dispatchFitSystemWindows(Rect insets) { fitSystemWindows(insets); } |
它直接调用View的fitSystemWindows方法。看View的fitSystemWindows方法。
1 | protected boolean fitSystemWindows(Rect insets) { if ((mPrivateFlags3 & PFLAG3_APPLYING_INSETS) == 0) { if (insets == null) { // Null insets by definition have already been consumed. // This call cannot apply insets since there are none to apply, // so return false. return false; } try { mPrivateFlags3 |= PFLAG3_FITTING_SYSTEM_WINDOWS; return dispatchApplyWindowInsets(new WindowInsets(insets)).isConsumed(); } finally { mPrivateFlags3 &= ~PFLAG3_FITTING_SYSTEM_WINDOWS; } } else { return fitSystemWindowsInt(insets); } } |
由于第一次调用,这里的mPrivateFlags3 的PFLAG3_APPLYING_INSETS标志为不为1,所以进入if条件。进入dispatchApplyWindowInsets方法。并将mPrivateFlags3 的PFLAG3_APPLYING_INSETS标志为置为1。由于ContentFrameLayout继承了Framelayout ,所以进入了ViewGroup的dispatchApplyWindowInsets方法。1
@Override
public WindowInsets dispatchApplyWindowInsets(WindowInsets insets) {
insets = super.dispatchApplyWindowInsets(insets);
if (!insets.isConsumed()) {
final int count = getChildCount();
for (int i = 0; i < count; i++) {
insets = getChildAt(i).dispatchApplyWindowInsets(insets);
if (insets.isConsumed()) {
break;
}
}
}
return insets;
}
首先调用了 super.dispatchApplyWindowInsets方法,也就是View的 dispatchApplyWindowInsets,
然后如果insets没有被消费掉的话,分别调用每个view child的dispatchApplyWindowInsets方法,让子view去消费它,如果子view消费了,那么到此结束。先执行 super.dispatchApplyWindowInsets方法。
下面是View.dispatchApplyWindowInsets方法。1
public WindowInsets dispatchApplyWindowInsets(WindowInsets insets) {
try {
mPrivateFlags3 |= PFLAG3_APPLYING_INSETS;
if (mListenerInfo != null && mListenerInfo.mOnApplyWindowInsetsListener != null) {
return mListenerInfo.mOnApplyWindowInsetsListener.onApplyWindowInsets(this, insets);
} else {
return onApplyWindowInsets(insets);
}
} finally {
mPrivateFlags3 &= ~PFLAG3_APPLYING_INSETS;
}
}
在此方法中首先将mPrivateFlags3 的PFLAG3_APPLYING_INSETS标志位置为1,然后如果开发者设置了listener的话就调用listener,否则调用onApplyWindowInsets方法。
1 | public WindowInsets onApplyWindowInsets(WindowInsets insets) { if ((mPrivateFlags3 & PFLAG3_FITTING_SYSTEM_WINDOWS) == 0) { if (fitSystemWindows(insets.getSystemWindowInsets())) { return insets.consumeSystemWindowInsets(); } } else { if (fitSystemWindowsInt(insets.getSystemWindowInsets())) { return insets.consumeSystemWindowInsets(); } } return insets; } |
在第一次调用fitSystemWindows方法后,mPrivateFlags3 得 PFLAG3_FITTING_SYSTEM_WINDOWS标志为被置位1了,所以进入fitSystemWindowsInt方法。
1 | private boolean fitSystemWindowsInt(Rect insets) { if ((mViewFlags & FITS_SYSTEM_WINDOWS) == FITS_SYSTEM_WINDOWS) { mUserPaddingStart = UNDEFINED_PADDING; mUserPaddingEnd = UNDEFINED_PADDING; Rect localInsets = sThreadLocal.get(); if (localInsets == null) { localInsets = new Rect(); sThreadLocal.set(localInsets); } boolean res = computeFitSystemWindows(insets, localInsets); mUserPaddingLeftInitial = localInsets.left; mUserPaddingRightInitial = localInsets.right; internalSetPadding(localInsets.left, localInsets.top, localInsets.right, localInsets.bottom); return res; } return false; } |
在这个方法中,两个关键函数
- computeFitSystemWindows
- internalSetPadding
先看computeFitSystemWindows。官方解释是,计算insets应该被此view消费掉还是继续传递。
1 | protected boolean computeFitSystemWindows(Rect inoutInsets, Rect outLocalInsets) { if ((mViewFlags & OPTIONAL_FITS_SYSTEM_WINDOWS) == 0 || mAttachInfo == null || ((mAttachInfo.mSystemUiVisibility & SYSTEM_UI_LAYOUT_FLAGS) == 0 && !mAttachInfo.mOverscanRequested)) { outLocalInsets.set(inoutInsets); inoutInsets.set(0, 0, 0, 0); return true; } else { // The application wants to take care of fitting system window for // the content... however we still need to take care of any overscan here. final Rect overscan = mAttachInfo.mOverscanInsets; outLocalInsets.set(overscan); inoutInsets.left -= overscan.left; inoutInsets.top -= overscan.top; inoutInsets.right -= overscan.right; inoutInsets.bottom -= overscan.bottom; return false; } } |
再看internalSetPadding
此方法是设置view的padding。1
protected void internalSetPadding(int left, int top, int right, int bottom) {
mUserPaddingLeft = left;
mUserPaddingRight = right;
mUserPaddingBottom = bottom;
final int viewFlags = mViewFlags;
boolean changed = false;
// Common case is there are no scroll bars.
if ((viewFlags & (SCROLLBARS_VERTICAL|SCROLLBARS_HORIZONTAL)) != 0) {
if ((viewFlags & SCROLLBARS_VERTICAL) != 0) {
final int offset = (viewFlags & SCROLLBARS_INSET_MASK) == 0
? 0 : getVerticalScrollbarWidth();
switch (mVerticalScrollbarPosition) {
case SCROLLBAR_POSITION_DEFAULT:
if (isLayoutRtl()) {
left += offset;
} else {
right += offset;
}
break;
case SCROLLBAR_POSITION_RIGHT:
right += offset;
break;
case SCROLLBAR_POSITION_LEFT:
left += offset;
break;
}
}
if ((viewFlags & SCROLLBARS_HORIZONTAL) != 0) {
bottom += (viewFlags & SCROLLBARS_INSET_MASK) == 0
? 0 : getHorizontalScrollbarHeight();
}
}
if (mPaddingLeft != left) {
changed = true;
mPaddingLeft = left;
}
if (mPaddingTop != top) {
changed = true;
mPaddingTop = top;
}
if (mPaddingRight != right) {
changed = true;
mPaddingRight = right;
}
if (mPaddingBottom != bottom) {
changed = true;
mPaddingBottom = bottom;
}
if (changed) {
requestLayout();
}
}