Android檢視相關之Window.getDecorView()原始碼分析
摘要：
Window類為抽象類，首先檢視Window類的類註釋
/**
* Abstract base class for a top-level window look and behavior policy.An
* instance of this class should ...
Window類為抽象類，首先檢視Window類的類註釋
/**
* Abstract base class for a top-level window look and behavior policy.An
* instance of this class should be used as the top-level view added to the
* window manager. It provides standard UI policies such as a background, title
* area, default key processing, etc.
*
* <p>The only existing implementation of this abstract class is
* android.view.PhoneWindow, which you should instantiate when needing a
* Window.
*/
public abstract class Window {
}
Window類是定義視窗外觀樣式和行為規範的抽象基類，用於作為頂層的View加到WindowManager中；
PhoneWindow是它唯一的實現類。
那麼現在來看一下PhoneWindow
private DecorView mDecor;
@Override
public final View getDecorView() {
if (mDecor == null || mForceDecorInstall) {
installDecor();
}
return mDecor;
}
private void installDecor() {
mForceDecorInstall = false;
if (mDecor == null) {
mDecor = generateDecor(-1);
...
} else {
mDecor.setWindow(this);
}
if (mContentParent == null) {
mContentParent = generateLayout(mDecor);
...
}
}
-->
protected DecorView generateDecor(int featureId) {
...
return new DecorView(context, featureId, this, getAttributes());
}
//DecorView是個FrameLayout
public class DecorView extends FrameLayout implements RootViewSurfaceTaker, WindowCallbacks {
}
-->
protected ViewGroup generateLayout(DecorView decor) {
// Apply data from current theme.
TypedArray a = getWindowStyle();
//很長一段都是設定一些Window的屬性或者標誌；
...
// Inflate the window decor.
//根據設定好的window屬性標誌來選擇layout佈局， 賦值到layoutResource
int layoutResource;
int features = getLocalFeatures();
// System.out.println("Features: 0x" + Integer.toHexString(features));
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;
}
...
}
//還有多個window屬性的判斷，layoutResource賦值 ，和上面這一段基本一樣
...
mDecor.startChanging();//mChanging = true;修改標誌
mDecor.onResourcesLoaded(mLayoutInflater, layoutResource);//重點程式碼，請看下一段
ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);
if (contentParent == null) {
throw new RuntimeException("Window couldn't find content container view");
}
...
mDecor.finishChanging();
return contentParent;
}
小結：
1、generateDecor()用於new一個DecorView，賦值給mDecor；
2、generateLayout()設定window的一些屬性，根據屬性獲取對應的layout，然後執行mDecor.onResourcesLoaded(mLayoutInflater, layoutResource);
再繼續分析onResourcesLoaded(LayoutInflater inflater, int layoutResource) 方法
//onResourcesLoaded主要是把layoutResource inflate出來，新增到DecorView中
void onResourcesLoaded(LayoutInflater inflater, int layoutResource) {
mStackId = getStackId();
//mBackdropFrameRenderer 用於繪製背景的執行緒，不為空時先繪製DecorView的背景
if (mBackdropFrameRenderer != null) {
loadBackgroundDrawablesIfNeeded();
mBackdropFrameRenderer.onResourcesLoaded(
this, mResizingBackgroundDrawable, mCaptionBackgroundDrawable,
mUserCaptionBackgroundDrawable, getCurrentColor(mStatusColorViewState),
getCurrentColor(mNavigationColorViewState));
}
//window的標題View,顯示與否取決於window的型別和作用場景
mDecorCaptionView = createDecorCaptionView(inflater);
final View root = inflater.inflate(layoutResource, null);//建立這個layoutResource 的 View 例項物件 root
if (mDecorCaptionView != null) {
// 先新增 mDecorCaptionView（如果不為null）,再向 mDecorCaptionView 中新增 root
if (mDecorCaptionView.getParent() == null) {
addView(mDecorCaptionView,
new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));
}
mDecorCaptionView.addView(root,
new ViewGroup.MarginLayoutParams(MATCH_PARENT, MATCH_PARENT));
} else {
// Put it below the color views.
addView(root, 0, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));
}
mContentRoot = (ViewGroup) root;
initializeElevation();
}
把layoutResource inflate出來，新增到DecorView中
總結 PhoneWindow.getDecorView()
如果是第一次呼叫mWindow.getDecorView()方法時，mDecor 為空，執行installDecor()，步驟如下：
1、執行generateDecor()方法，new一個DecorView ，賦值到變數mDecor ；
2、執行generateLayout(DecorView decor)方法，把mDecor 傳睇進去；
（2.1）獲取主題設定，配置一些Window的屬性標誌；
（2.2）根據Window的屬性標誌，給layoutResource選擇對應的layout賦值，這些layout的共同點是都包含一個id為@android:id/content的layout；
（2.3）把2.2步驟的layoutResource inflate成view，用addview最終新增到DecorView的中。