问题描述
在最近的项目中，遇到一个奇葩问题。起初为了解决打开app白屏或者黑屏问题，在SplashActivity的Theme里面添加属性：
<item name="android:windowBackground">@drawable/splash_activity_launch _bg</item>
drawable设置背景色为白色，并在中间放置了一张图片
<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
<item android:drawable="@android:color/white" />
<item>
<bitmap
android:gravity="center"
android:src="@mipmap/splash_logo" />
</item>
</layer-list>
为了不显得突兀，在SplashActivity的布局activity_splash.xml中间也放置了一张相同的图片
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/rl_splash_root"
android:layout_width="match_parent"
android:layout_height="match_parent">
<ImageView
android:id="@+id/iv_splash_logo"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerInParent="true"
android:src="@mipmap/splash_logo" />
</RelativeLayout>
但奇怪的是两张图片居然错位了(两张图片为什么会一起显示是由于背景色导致的，此次不必追究)。具体效果看图：
matter.gif
这里不妨大胆猜测activity_splash.xml所代表的区域和windowBackground所代表的区域并不一致，那他们各自所代表的区域是什么呢，下面我们就跟随源码一步步的分析。
分析步骤
activity_splash.xml即通常说的内容区域，绘制的控件都显示在其中，一般我们通过setContentView()添加到activity中（必须继承Activity，AppCompatActivity源码不同），点击去看一下源码。里面调用了抽象类Window的抽象方法setContentView()
public void setContentView(@LayoutRes int layoutResID) {
getWindow().setContentView(layoutResID);
initWindowDecorActionBar();
}
public abstract class Window {
public abstract void setContentView(@LayoutRes int layoutResID);
}
搜索一下实现类,可以看到实现类为PhoneWindow
mWindow = new PhoneWindow(this, window, activityConfigCallback);
mWindow.setWindowControllerCallback(this);
mWindow.setCallback(this);
mWindow.setOnWindowDismissedCallback(this);
mWindow.getLayoutInflater().setPrivateFactory(this);
去看一下实现类PhoneWindow的setContentView()方法，这里主要完成了两件事，调用installDecor()方法和将传入的layoutResID(就是activity根布局)布局添加到mContentParent中。mContentParent还不知道是什么，但是它肯定在installDecor()方法中被初始化了。
@Override
public void setContentView(int layoutResID) {
//第一次mContentParent是空值，执行installDecor()方法
if (mContentParent == null) {
installDecor();
} else if (!hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
mContentParent.removeAllViews();
}
if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
final Scene newScene = Scene.getSceneForLayout(mContentParent, layoutResID,
getContext());
transitionTo(newScene);
} else {
//将传入的布局layoutResID布局添加到mContentParent中
mLayoutInflater.inflate(layoutResID, mContentParent);
}
installDecor()主要调用了两个方法generateDecor()和generateLayout()，generateDecor()方法的返回值是mDecor ，generateLayout(mDecor)方法的返回值是mContentParent 。
private void installDecor() {
mForceDecorInstall = false;
if (mDecor == null) {
//第一次mDecor为空
mDecor = generateDecor(-1);
mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);
mDecor.setIsRootNamespace(true);
if (!mInvalidatePanelMenuPosted && mInvalidatePanelMenuFeatures != 0) {
mDecor.postOnAnimation(mInvalidatePanelMenuRunnable);
}
} else {
mDecor.setWindow(this);
}
if (mContentParent == null) {
//此时mContentParent 被初始化
mContentParent = generateLayout(mDecor);
先看一下generateDecor()方法，这里直接new了一个DecorView，DecorView继承FrameLayout 。
protected DecorView generateDecor() {
return new DecorView(getContext(), -1);
}
private final class DecorView extends FrameLayout implements RootViewSurfaceTaker {
private final int mFeatureId;
private final Rect mDrawingBounds = new Rect();
private final Rect mBackgroundPadding = new Rect();
回过头继续看一下generateLayout()方法，此方法主要是根据样式选择相应的布局、将此布局添加到mDecor中，并初始化mContentParent。留意下面的"ID_ANDROID_CONTENT "
protected ViewGroup generateLayout(DecorView decor) {
//获取设置的Window样式，这里说明设置全屏、隐藏标题栏等必须在setContentView()之前
TypedArray a = getWindowStyle();
........
//下面的代码，主要是根据样式和属性选择对应的布局，这个布局是什么，待会解释；
int layoutResource;
int features = getLocalFeatures();
if ((features & (1 << FEATURE_SWIPE_TO_DISMISS)) != 0) {
layoutResource = R.layout.screen_swipe_dismiss;
} else if ((features & ((1 << FEATURE_LEFT_ICON) | (1 << FEATURE_RIGHT_ICON))) != 0) {
if (mIsFloating) {
TypedValue res = new TypedValue();
getContext().getTheme().resolveAttribute(
R.attr.dialogTitleIconsDecorLayout, res, true);
layoutResource = res.resourceId;
} else {
layoutResource = R.layout.screen_title_icons;
}
removeFeature(FEATURE_ACTION_BAR);
} else if ((features & ((1 << FEATURE_PROGRESS) | (1 << FEATURE_INDETERMINATE_PROGRESS))) != 0
&& (features & (1 << FEATURE_ACTION_BAR)) == 0) {
layoutResource = R.layout.screen_progress;
} else if ((features & (1 << FEATURE_CUSTOM_TITLE)) != 0) {
if (mIsFloating) {
TypedValue res = new TypedValue();
getContext().getTheme().resolveAttribute(
R.attr.dialogCustomTitleDecorLayout, res, true);
layoutResource = res.resourceId;
} else {
layoutResource = R.layout.screen_custom_title;
}
removeFeature(FEATURE_ACTION_BAR);
} else if ((features & (1 << FEATURE_NO_TITLE)) == 0) {
if (mIsFloating) {
TypedValue res = new TypedValue();
getContext().getTheme().resolveAttribute(
R.attr.dialogTitleDecorLayout, res, true);
layoutResource = res.resourceId;
} else if ((features & (1 << FEATURE_ACTION_BAR)) != 0) {
layoutResource = a.getResourceId(
R.styleable.Window_windowActionBarFullscreenDecorLayout,
//含有ActionBar的布局
R.layout.screen_action_bar);
} else {
//含有TitleBar的布局
layoutResource = R.layout.screen_title;
}
} else if ((features & (1 << FEATURE_ACTION_MODE_OVERLAY)) != 0) {
layoutResource = R.layout.screen_simple_overlay_action_mode;
} else {
//最常用布局
layoutResource = R.layout.screen_simple;
}
mDecor.startChanging();
//将layoutResource 转化为View
View in = mLayoutInflater.inflate(layoutResource, null);
//将View添加到Decor中
decor.addView(in, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));
mContentRoot = (ViewGroup) in;
//注意这个ID： public static final int ID_ANDROID_CONTENT = com.android.internal.R.id.content;
//这里说明mContentParent对象就是ID_ANDROID_CONTENT代表的布局
ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);
if (contentParent == null) {
throw new RuntimeException("Window couldn't find content container view");
}
上面提到了根据样式Style选择相应的布局，但是这个布局到底是什么呢。可以用SearchEverything搜索R.layout.screen_simple、R.layout.screen_title、R.layout.screen_action_bar几个常用的布局看一下。
screen_simple:普通布局
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
android:orientation="vertical">
<ViewStub android:id="@+id/action_mode_bar_stub"
android:inflatedId="@+id/action_mode_bar"
android:layout="@layout/action_mode_bar"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:theme="?attr/actionBarTheme" />
<FrameLayout
<!--记住这个ID-->
android:id="@android:id/content"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:foregroundInsidePadding="false"
android:foregroundGravity="fill_horizontal|top"
android:foreground="?android:attr/windowContentOverlay" />
</LinearLayout>
screen_title:含有TitleBar的布局
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:fitsSystemWindows="true">
<!-- Popout bar for action modes -->
<ViewStub android:id="@+id/action_mode_bar_stub"
android:inflatedId="@+id/action_mode_bar"
android:layout="@layout/action_mode_bar"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:theme="?attr/actionBarTheme" />
<FrameLayout
android:layout_width="match_parent"
android:layout_height="?android:attr/windowTitleSize"
style="?android:attr/windowTitleBackgroundStyle">
<TextView android:id="@android:id/title"
style="?android:attr/windowTitleStyle"
android:background="@null"
android:fadingEdge="horizontal"
android:gravity="center_vertical"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</FrameLayout>
<FrameLayout
<!--记住这个ID-->
android:id="@android:id/content"
android:layout_width="match_parent"
android:layout_height="0dip"
android:layout_weight="1"
android:foregroundGravity="fill_horizontal|top"
android:foreground="?android:attr/windowContentOverlay" />
</LinearLayout>
screen_action_bar:含有ActionBar的布局
<com.android.internal.widget.ActionBarOverlayLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/decor_content_parent"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:splitMotionEvents="false"
android:theme="?attr/actionBarTheme">
<FrameLayout
<!--记住这个ID-->
android:id="@android:id/content"
android:layout_width="match_parent"
android:layout_height="match_parent" />
<com.android.internal.widget.ActionBarContainer
android:id="@+id/action_bar_container"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
style="?attr/actionBarStyle"
android:transitionName="android:action_bar"
android:touchscreenBlocksFocus="true"
android:keyboardNavigationCluster="true"
android:gravity="top">
<com.android.internal.widget.ActionBarView
android:id="@+id/action_bar"
android:layout_width="match_parent"
android:layout_height="wrap_content"
style="?attr/actionBarStyle" />
<com.android.internal.widget.ActionBarContextView
android:id="@+id/action_context_bar"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:visibility="gone"
style="?attr/actionModeStyle" />
</com.android.internal.widget.ActionBarContainer>
<com.android.internal.widget.ActionBarContainer android:id="@+id/split_action_bar"
android:layout_width="match_parent"
android:layout_height="wrap_content"
style="?attr/actionBarSplitStyle"
android:visibility="gone"
android:touchscreenBlocksFocus="true"
android:keyboardNavigationCluster="true"
android:gravity="center"/>
</com.android.internal.widget.ActionBarOverlayLayout>
上面三个分别代表了常用布局、含有TitleBar的布局、含有ActionBar的布局，原来TitleBar、ActionBar这些也是写在布局文件中的，其实一点也不神奇。来看一下这些布局的共性，会发现这些布局的根布局都是LinearLayout,且都有一个id为"@android:id/content"的FrameLayout，其实mContentParent其实就是布局里面的FrameLayout
<FrameLayout
android:id="@android:id/content"
android:layout_width="match_parent"
android:layout_height="match_parent"
/>
现在来梳理一下：
- layoutResID----------添加到----------mContentParent
mLayoutInflater.inflate(layoutResID, mContentParent);
- mContentParent----------等于----------FrameLayout
//调用setContentView()方法就是把布局添加到FrameLayout中
ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);
- FrameLayout----------添加到----------mDecor
View in = mLayoutInflater.inflate(layoutResource, null);
decor.addView(in, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));
DecorView什么时候被添加到Window中呢？这里就不一步步的看了，在ActivityThread.java的handleResumeActivity()方法中。
final void handleResumeActivity(IBinder token,
boolean clearHide, boolean isForward, boolean reallyResume, int seq, String reason) {
ActivityClientRecord r = mActivities.get(token);
if (!checkAndUpdateLifecycleSeq(seq, r, "resumeActivity")) {
return;
}
unscheduleGcIdler();
mSomeActivitiesChanged = true;
r = performResumeActivity(token, clearHide, reason);
if (r != null) {
final Activity a = r.activity;
if (localLOGV) Slog.v(
final int forwardBit = isForward ? WindowManager.LayoutParams.SOFT_INPUT_IS_FORWARD_NAVIGATION : 0;
boolean willBeVisible = !a.mStartedActivity;
if (!willBeVisible) {
try {
willBeVisible = ActivityManager.getService().willActivityBeVisible(
a.getActivityToken());
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
}
if (r.window == null && !a.mFinished && willBeVisible) {
r.window = r.activity.getWindow();
View decor = r.window.getDecorView();
decor.setVisibility(View.INVISIBLE);
ViewManager wm = a.getWindowManager();
WindowManager.LayoutParams l = r.window.getAttributes();
a.mDecor = decor;
l.type = WindowManager.LayoutParams.TYPE_BASE_APPLICATION;
l.softInputMode |= forwardBit;
if (r.mPreserveWindow) {
a.mWindowAdded = true;
r.mPreserveWindow = false;
ViewRootImpl impl = decor.getViewRootImpl();
if (impl != null) {
impl.notifyChildRebuilt();
}
}
if (a.mVisibleFromClient) {
if (!a.mWindowAdded) {
a.mWindowAdded = true;
wm.addView(decor, l);//将DecorView添加到Window中
} else {
a.onWindowAttributesChanged(l);
}
}
DecorView为整个Window界面的最顶层View，且只含有一个子元素LinearLayout。也就是FrameLayout的根元素，如果不信的话，可以尝试打开更多的布局，结果无一另外全是LinearLayout(ActionBar的根布局ActionBarOverlayLayout继承LinearLayout)。
layout.png
下面来区分几个activity界面的常用概念，以便理解。
app.png
绿色区域:状态栏StatusBar，高度计算如下：
public static int getStatusBarHeight(Context context) {
int statusBarHeight = 0;
int resourceId = context.getResources().getIdentifier("status_bar_height", "dimen", "android");
if (resourceId > 0) {
statusBarHeight = context.getResources().getDimensionPixelSize(resourceId);
}
return statusBarHeight;
}
紫色部分:ActionBar或者TitleBar ，高度计算如下
public static int getTitleBarHeight(Activity context) {
int top = context.getWindow().findViewById(Window.ID_ANDROID_CONTENT).getTop();
return top > getStatusBarHeight(context) ? top - getStatusBarHeight(context) : 0;
}
黄色部分:RootView(也叫内容区域),高度计算如下
public static int getRootView(Activity context) {
return context.getWindow().findViewById(Window.ID_ANDROID_CONTENT).getHeight();
}
红色部分:导航栏NavigationBar，高度计算如下
public static int getNavigationBarHeight(Context context) {
int resourceId = context.getResources().getIdentifier("navigation_bar_height", "dimen", "android");
return context.getResources().getDimensionPixelSize(resourceId);
}
应用区域:内容区域+紫色区域(RootView+TitleBar/ActionBar)
public static int getContentViewHeight(Activity context) {
Rect outRect = new Rect();
context.getWindow().getDecorView().getWindowVisibleDisplayFrame(outRect);
return outRect.height();
}
这里要重点说明一下，通常getDisplayMetrics().heightPixels方法拿到的分辨率的高度不一定是真的分辨率高度，具体详情查看Android手机获取屏幕分辨率高度因虚拟导航栏带来的问题
到了这里我们就可以大致推断DecorView的高度了
DecorViewHeight=RootView+TitleBar/ActionBar+StatusBarHeight;
或者
DecorViewHeight=RootView+TitleBar/ActionBar+StatusBarHeight+NavigationBarHeight;
这里是不是很困惑了？高度怎么把StatusBarHeight和NavigationBar算进去了。原来StatusBar和NavigationBar都是系统UI，每一个Activity在绘制的时候都会预留空间给StatusBar和NavigationBar,占据DecorView空间但不属于DecorView本身。那为什么DecorView高度有时包括NavigationBar有时不包括呢，这主要是由各个系统版本和Style决定的，具体源码在何处现在没有去分析。总之DecorView高度并不是固定的是可以动态变化的，举个栗子吧！
例子
1、首先隐藏StatusBar和NavigationBar
View decorView = getWindow().getDecorView();
int uiOptions = View.SYSTEM_UI_FLAG_HIDE_NAVIGATION
| View.SYSTEM_UI_FLAG_FULLSCREEN;
decorView.setSystemUiVisibility(uiOptions);
setContentView(R.layout.activity_splash);
2、在onWindowFocusChanged()方法中打印DecorView高度
@Override
public void onWindowFocusChanged(boolean hasFocus) {
super.onWindowFocusChanged(hasFocus);
Log.e("decorViewHeight ", getWindow().getDecorView().getHeight() + "");
Log.e("DisplayHeight ", UIUtil.getDisplayHeight(this) + "");
Log.e("RealMetricsHeight ", UIUtil.getRealMetrics(this) + "");
Log.e("stateBarHeight ", UIUtil.getStatusBarHeight(this) + "");
Log.e("TitleBarHeight ", UIUtil.getTitleBarHeight(this) + "");
Log.e("ActionBarHeight ", UIUtil.getActionBarHeight(this) + "");
Log.e("NavigationBarHeight ", UIUtil.getNavigationBarHeight(this) + "");
Log.e("rootViewHeight ", UIUtil.getRootView(this) + "");
Log.e("contentViewHeight", UIUtil.getContentViewHeight(this) + "");
}
3、打印日志如下
07-08 20:33:43.568 5731-5731/paradise.decoarview E/decorViewHeight: 1280
07-08 20:33:43.568 5731-5731/paradise.decoarview E/DisplayHeight: 1244
07-08 20:33:43.578 5731-5731/paradise.decoarview E/RealMetricsHeight: 1280
07-08 20:33:43.578 5731-5731/paradise.decoarview E/stateBarHeight: 38
07-08 20:33:43.578 5731-5731/paradise.decoarview E/TitleBarHeight: 46
07-08 20:33:43.578 5731-5731/paradise.decoarview E/ActionBarHeight: 0
07-08 20:33:43.578 5731-5731/paradise.decoarview E/NavigationBarHeight: 36
07-08 20:33:43.578 5731-5731/paradise.decoarview E/rootViewHeight: 1158
07-08 20:33:43.578 5731-5731/paradise.decoarview E/contentViewHeight: 1242
4、点击一下屏幕，唤起NavigationBar、按返回键，打印日志如下
07-08 20:36:22.548 5731-5731/paradise.decoarview E/decorViewHeight: 1244
07-08 20:36:22.548 5731-5731/paradise.decoarview E/DisplayHeight: 1244
07-08 20:36:22.548 5731-5731/paradise.decoarview E/RealMetricsHeight: 1280
07-08 20:36:22.548 5731-5731/paradise.decoarview E/stateBarHeight: 38
07-08 20:36:22.548 5731-5731/paradise.decoarview E/TitleBarHeight: 46
07-08 20:36:22.548 5731-5731/paradise.decoarview E/ActionBarHeight: 0
07-08 20:36:22.548 5731-5731/paradise.decoarview E/NavigationBarHeight: 36
07-08 20:36:22.548 5731-5731/paradise.decoarview E/rootViewHeight: 1122
07-08 20:36:22.548 5731-5731/paradise.decoarview E/contentViewHeight: 1206
DecorView高度由1280变成了1244，而这个高度正好是NavigationBar高度。
问题解决
到了这里，一且都明白了。原来在本项目中
activity_splash.xml高度=RootView高度+ActionBarHeight/TitleBarHeight
WindowBackground高度=RootView高度+ActionBarHeight/TitleBarHeight+StatusBarHeight
多了一个StatusBarHeight,所以需要在初始化的时候RootView减去StatusBarHeight
FrameLayout.LayoutParams params = (FrameLayout.LayoutParams) rlSplashRoot.getLayoutParams();
params.topMargin = UIUtil.getStatusBarHeight();
rlSplashRoot.setLayoutParams(params);
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