Android檢視相關之setContentView()原始碼分析

原始碼分析安卓開發 · 發表 2019-04-27 23:11:26

摘要：日常使用Activity時都會用到setContentView(int layoutId)的方法，今天挖一下相關的原始碼，方便日後裝逼（學會這個好像最直接的作用就是可以裝逼） 1、setContentView(int layoutId) （基於Android8.1） @Ov...

日常使用Activity時都會用到setContentView(int layoutId)的方法，今天挖一下相關的原始碼，方便日後裝逼
（學會這個好像最直接的作用就是可以裝逼）

1、setContentView(int layoutId)

（基於Android8.1）

@Override
public void setContentView(@LayoutRes int layoutResID) {
getDelegate().setContentView(layoutResID);
}

-->
@NonNull
public AppCompatDelegate getDelegate() {
if (mDelegate == null) {
mDelegate = AppCompatDelegate.create(this, this);
}
return mDelegate;
}

-->
/**
*AppCompatDelegateImplV9是下面幾個AppCompatDelegateImplX 類的父類
*setContentView在AppCompatDelegateImplV9中實現
*/
private static AppCompatDelegate create(Context context, Window window,
AppCompatCallback callback) {
if (Build.VERSION.SDK_INT >= 24) {
return new AppCompatDelegateImplN(context, window, callback);
} else if (Build.VERSION.SDK_INT >= 23) {
return new AppCompatDelegateImplV23(context, window, callback);
} else if (Build.VERSION.SDK_INT >= 14) {
return new AppCompatDelegateImplV14(context, window, callback);
} else if (Build.VERSION.SDK_INT >= 11) {
return new AppCompatDelegateImplV11(context, window, callback);
} else {
return new AppCompatDelegateImplV9(context, window, callback);
}
}

setContentView在AppCompatDelegateImplV9中實現，其他類最終都繼承了AppCompatDelegateImplV9，呼叫AppCompatDelegateImplV9中的setContentView() 。

class AppCompatDelegateImplV9{

private ViewGroup mSubDecor;
@Override
public void setContentView(int resId) {
ensureSubDecor();
ViewGroup contentParent = (ViewGroup) mSubDecor.findViewById(android.R.id.content);
contentParent.removeAllViews();
LayoutInflater.from(mContext).inflate(resId, contentParent);//常見的inflate layout
mOriginalWindowCallback.onContentChanged();//呼叫onContentChanged（）的生命週期方法
}

-->
private void ensureSubDecor() {
if (!mSubDecorInstalled) {
mSubDecor = createSubDecor();//初始化mSubDecor

mSubDecorInstalled = true;//標記mSubDecor已經初始化

...
}
}
}

重點方法在createSubDecor(), 會關聯到了PhoneWindow和DecorView。

2、createSubDecor()

private ViewGroup createSubDecor() {
//獲取主題屬性
TypedArray a = mContext.obtainStyledAttributes(R.styleable.AppCompatTheme);

//根據activity設定的window屬性，配置activity風格樣式
if (a.getBoolean(R.styleable.AppCompatTheme_windowNoTitle, false)) {
requestWindowFeature(Window.FEATURE_NO_TITLE);//無title
} else if (a.getBoolean(R.styleable.AppCompatTheme_windowActionBar, false)) {
// Don't allow an action bar if there is no title.
requestWindowFeature(FEATURE_SUPPORT_ACTION_BAR);//設定actionbar
}
if (a.getBoolean(R.styleable.AppCompatTheme_windowActionBarOverlay, false)) {
//ActionBar的Overlay模式，讓ActionBar浮動且透明
requestWindowFeature(FEATURE_SUPPORT_ACTION_BAR_OVERLAY);
}
if (a.getBoolean(R.styleable.AppCompatTheme_windowActionModeOverlay, false)) {
requestWindowFeature(FEATURE_ACTION_MODE_OVERLAY);
}
mIsFloating = a.getBoolean(R.styleable.AppCompatTheme_android_windowIsFloating, false);//懸浮
a.recycle();

// Now let's make sure that the Window has installed its decor by retrieving it
mWindow.getDecorView();//給mWindow建立一個DecorView

final LayoutInflater inflater = LayoutInflater.from(mContext);
ViewGroup subDecor = null;//subDecor會作為結果返回出去

//根據主題屬性的標誌來決定實現哪個layout，然後賦值給subDecor 
if (!mWindowNoTitle) {
if (mIsFloating) {
// If we're floating, inflate the dialog title decor
subDecor = (ViewGroup) inflater.inflate(
R.layout.abc_dialog_title_material, null);
} else if (mHasActionBar) {
// Now inflate the view using the themed context and set it as the content view
subDecor = (ViewGroup) LayoutInflater.from(themedContext)
.inflate(R.layout.abc_screen_toolbar, null);
...
}
} else {
if (mOverlayActionMode) {
subDecor = (ViewGroup) inflater.inflate(
R.layout.abc_screen_simple_overlay_action_mode, null);
} else {
subDecor = (ViewGroup) inflater.inflate(R.layout.abc_screen_simple, null);
}
}
...

//獲取內容contentView,上面的四個layout中都有id為action_bar_activity_content的子view
final ContentFrameLayout contentView = (ContentFrameLayout) subDecor.findViewById(
R.id.action_bar_activity_content);

// 獲取PhoneWindow中的content佈局物件，這裡其實就是mWindow的mContentParent
final ViewGroup windowContentView = (ViewGroup) mWindow.findViewById(android.R.id.content);
if (windowContentView != null) {
// There might be Views already added to the Window's content view so we need to
// migrate them to our content view
//如果mWindow的contentview已經新增過一些view，把第一個子view放到我們contentView裡面
while (windowContentView.getChildCount() > 0) {
final View child = windowContentView.getChildAt(0);
windowContentView.removeViewAt(0);
contentView.addView(child);
}

// Change our content FrameLayout to use the android.R.id.content id.
// Useful for fragments.
//把mWindow中的mContentParent的id修改成View.NO_ID，原來的id是android:id/content
windowContentView.setId(View.NO_ID);
contentView.setId(android.R.id.content);
}

// Now set the Window's content view with the decor
mWindow.setContentView(subDecor);//把subDecor設定成mWindow的內容畫面
...
return subDecor;
}

解析：
1、首先配置window的屬性樣式（看3.1的程式碼片段）；
2、然後呼叫了 mWindow.getDecorView() ，即在window類中新建一個DecorView（FrameLayout），根據設定好的window屬性樣式inflate對應的layout佈局生成一個View，新增成為DecorView的子View。
3、根據屬性樣式的標誌載入對應的佈局，設定為subDecor(ViewGroup)的佈局；
4、執行mWindow.setContentView(subDecor)。

(2.1) requestWindowFeature(int featureId)

@Override
public boolean requestWindowFeature(int featureId) {
...
switch (featureId) {
case FEATURE_SUPPORT_ACTION_BAR:
throwFeatureRequestIfSubDecorInstalled();
mHasActionBar = true;// 改變屬性的標記
return true;
...
}
return mWindow.requestFeature(featureId);//設定window的屬性
}

// 如果在setContentView之後再去設定requestWindowFeature，會丟擲Exception。
private void throwFeatureRequestIfSubDecorInstalled() {
if (mSubDecorInstalled) {
throw new AndroidRuntimeException(
"Window feature must be requested before adding content");
}
}

(2.2) 看看subDecor設定的layout佈局

R.layout.abc_dialog_title_material（在include佈局中包含了id為action_bar_activity_content的ContentFrameLayout）

<android.support.v7.widget.FitWindowsLinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_height="match_parent"
android:layout_width="match_parent"
android:orientation="vertical"
android:fitsSystemWindows="true">
<TextView
android:id="@+id/title"
style="?android:attr/windowTitleStyle"
android:singleLine="true"
android:ellipsize="end"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:textAlignment="viewStart"
android:paddingLeft="?attr/dialogPreferredPadding"
android:paddingRight="?attr/dialogPreferredPadding"
android:paddingTop="@dimen/abc_dialog_padding_top_material"/>
<include
layout="@layout/abc_screen_content_include"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="1"/>
</android.support.v7.widget.FitWindowsLinearLayout>

R.layout.abc_screen_simple（在include佈局中包含了id為action_bar_activity_content的ContentFrameLayout）

<android.support.v7.widget.FitWindowsLinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/action_bar_root"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:fitsSystemWindows="true">

<android.support.v7.widget.ViewStubCompat
android:id="@+id/action_mode_bar_stub"
android:inflatedId="@+id/action_mode_bar"
android:layout="@layout/abc_action_mode_bar"
android:layout_width="match_parent"
android:layout_height="wrap_content" />

<include layout="@layout/abc_screen_content_include" />

</android.support.v7.widget.FitWindowsLinearLayout>

3、mWindow.setContentView(View view)

@Override
public void setContentView(View view) {
setContentView(view, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));
}

@Override
public void setContentView(View view, ViewGroup.LayoutParams params) {
// Note: FEATURE_CONTENT_TRANSITIONS may be set in the process of installing the window
// decor, when theme attributes and the like are crystalized. Do not check the feature
// before this happens. 
if (mContentParent == null) {
installDecor();//如果mWindow中的mContentParent 為null，執行installDecor()會初始化mContentParent
} else if (!hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
mContentParent.removeAllViews();
}

if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
view.setLayoutParams(params);
final Scene newScene = new Scene(mContentParent, view);
transitionTo(newScene);
} else {
//把subDecor新增到了window中
mContentParent.addView(view, params);
}
...
}

解析：mWindow.setContentView(subDecor)就是把mSubDecor新增到mWindow的mContentParent佈局中。

4、再回到setContentView

public void setContentView(int resId) {
ensureSubDecor();
ViewGroup contentParent = (ViewGroup) mSubDecor.findViewById(android.R.id.content);
contentParent.removeAllViews();//清空contentParent佈局中的子控制元件
LayoutInflater.from(mContext).inflate(resId, contentParent);//把我們設定的layout新增到contentParent中
mOriginalWindowCallback.onContentChanged();//呼叫onContentChanged（）的生命週期方法
}

從mSubDecor中獲取contentParent的佈局，把我們設定的layout新增到contentParent中。

總結：

1、Activity中有一個window(PhoneWindow), 配置主題屬性就是經過這個window;

2、Activity檢視層級中的根佈局是DecorView，這是個FrameLayout。

3、我們設定的佈局到DecorView之間還存在三個或者四個佈局。

Activity檢視層級.png

結論驗證

寫個demo,佈局頁面如下

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">

<Button
android:id="@+id/btn"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Hello World!"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent" />

</android.support.constraint.ConstraintLayout>

preview.png

在來看一下檢視層級

檢視層級分析.JPG