setcontentview源码简单分析

首先我们先进入 *setContentView 这个方法

  * @param layoutResID Resource ID to be inflated.
  *
 * @see #setContentView(android.view.View)
 * @see #setContentView(android.view.View, android.view.ViewGroup.LayoutParams)
 */
public void setContentView(@LayoutRes int layoutResID) {
    getWindow().setContentView(layoutResID);
    initWindowDecorActionBar();
}
public Window getWindow() {
    return mWindow;
}
 public abstract void setContentView(@LayoutRes int layoutResID);

可以看到这只是一个抽象类 说明我们找的地方找错了 我们应该去找mWindow赋值的地方所以我们来到了attach 这个方法

    final void attach(...) {
    attachBaseContext(context);

    mFragments.attachHost(null /*parent*/);

    mWindow = new PhoneWindow(this, window, activityConfigCallback);
    mWindow.setWindowControllerCallback(this);
    mWindow.setCallback(this);
    mWindow.setOnWindowDismissedCallback(this);
    mWindow.getLayoutInflater().setPrivateFactory(this);
    if (info.softInputMode != WindowManager.LayoutParams.SOFT_INPUT_STATE_UNSPECIFIED) {
        mWindow.setSoftInputMode(info.softInputMode);
    }
    if (info.uiOptions != 0) {
        mWindow.setUiOptions(info.uiOptions);
    }
    mUiThread = Thread.currentThread();
      ....
    mLastNonConfigurationInstances = lastNonConfigurationInstances;
    if (voiceInteractor != null) {
        if (lastNonConfigurationInstances != null) {
            mVoiceInteractor = lastNonConfigurationInstances.voiceInteractor;
        } else {
            mVoiceInteractor = new VoiceInteractor(voiceInteractor, this, this,
                    Looper.myLooper());
        }
    }

    mWindow.setWindowManager(
            (WindowManager)context.getSystemService(Context.WINDOW_SERVICE),
            mToken, mComponent.flattenToString(),
            (info.flags & ActivityInfo.FLAG_HARDWARE_ACCELERATED) != 0);
    if (mParent != null) {
        mWindow.setContainer(mParent.getWindow());
    }
    mWindowManager = mWindow.getWindowManager();
    mCurrentConfig = config;

    mWindow.setColorMode(info.colorMode);

    setAutofillCompatibilityEnabled(application.isAutofillCompatibilityEnabled());
    enableAutofillCompatibilityIfNeeded();
}

我们可以从 mWindow = new PhoneWindow(this, window, activityConfigCallback);这句代码中 看出 它New了一个 PhoneWindow 的实例 我们再接着去看下 ,而点开PhoneWindow的源码我们会发现它继承自Window类,由此我们可以知道,PhoneWindow类是Window的具体实现类.
我们继续看setcontentView()这个方法的实现

 @Override
   public void setContentView(int layoutResID) {
    // 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) {//当mContentParent为空的时候 也就是没有放置父布局 
        installDecor();
    } else if (!hasFeature(FEATURE_CONTENT_TRANSITIONS)) {//有没有使用过度动画，也就是转场动画
        mContentParent.removeAllViews();
    }

    if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
        final Scene newScene = Scene.getSceneForLayout(mContentParent, layoutResID,
                getContext());//利用Scene来过度启动
        transitionTo(newScene);
    } else {
        mLayoutInflater.inflate(layoutResID, mContentParent);//否则则通过LayoutInflater对象转换为View树，并且添加至mContentParent视图中。
    }
    mContentParent.requestApplyInsets();
    final Callback cb = getCallback();
    if (cb != null && !isDestroyed()) {
        cb.onContentChanged();
    }
    mContentParentExplicitlySet = true;
}

首先他做了一个if (mContentParent == null)判断 我们先来看下这个是啥

// This is the view in which the window contents are placed. It is either
// mDecor itself, or a child of mDecor where the contents go.
ViewGroup mContentParent;  

可以看到他只是一个ViewGroup 结合注释 翻译过来的内容就是（这是放置窗口内容的视图。 它是mDecor本身，或内容的mDecor的子布局。） 我们接着去看installDecor()

private void installDecor() {
mForceDecorInstall = false;
if (mDecor == null) {//判断是否为空
mDecor = generateDecor(-1);//重新NEW一个Decor 实例 mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);
mDecor.setIsRootNamespace(true);
if (!mInvalidatePanelMenuPosted && mInvalidatePanelMenuFeatures != 0) {
mDecor.postOnAnimation(mInvalidatePanelMenuRunnable);
}
} else {
mDecor.setWindow(this);
}
//一开始DecorView未加载到mContentParent，所以此时mContentParent=null
if (mContentParent == null) {
mContentParent = generateLayout(mDecor);

        // Set up decor part of UI to ignore fitsSystemWindows if appropriate.
        mDecor.makeOptionalFitsSystemWindows();

        final DecorContentParent decorContentParent = (DecorContentParent)  mDecor.findViewById(
                R.id.decor_content_parent);
         ...设置title  转场动画等
        }

我们进入generateLayou 这个方法看下

   protected ViewGroup generateLayout(DecorView decor) {
    // Apply data from current theme.
。。。    
      if ((features & (1 << FEATURE_ACTION_MODE_OVERLAY)) != 0) {
        layoutResource = R.layout.screen_simple_overlay_action_mode;
    } else {
        // Embedded, so no decoration is needed.
        layoutResource = R.layout.screen_simple;
        // System.out.println("Simple!");
    }
    mDecor.startChanging();
     //加载资源
        mDecor.startChanging();
    mDecor.onResourcesLoaded(mLayoutInflater, layoutResource);
     //加载一个ID_ANDROID_CONTENT 布局
    ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);
    if (contentParent == null) {
        throw new RuntimeException("Window couldn't find content container view");
    }

  。。。
    // Remaining setup -- of background and title -- that only applies
    // to top-level windows.
    if (getContainer() == null) {
        final Drawable background;
        if (mBackgroundResource != 0) {
            background = getContext().getDrawable(mBackgroundResource);
        } else {
            background = mBackgroundDrawable;
        }
        mDecor.setWindowBackground(background);

        final Drawable frame;
        if (mFrameResource != 0) {
            frame = getContext().getDrawable(mFrameResource);
        } else {
            frame = null;
        }
        mDecor.setWindowFrame(frame);

        mDecor.setElevation(mElevation);
        mDecor.setClipToOutline(mClipToOutline);

        if (mTitle != null) {
            setTitle(mTitle);
        }

        if (mTitleColor == 0) {
            mTitleColor = mTextColor;
        }
        setTitleColor(mTitleColor);
    }

    mDecor.finishChanging();

    return contentParent;    }