Activity 的 Window 创建过程

Yif

发布于 2019-12-26 15:29:42

7030

发布于 2019-12-26 15:29:42

文章被收录于专栏：Android 进阶

Activity 的 Window 创建过程

Activity Window创建最终在ActivityThread 中的performLaunchActivity方法中，调用Activity的attach方法创建。

调用mWindow = new PhoneWindow(this, window, activityConfigCallback);进行初始化操作； Activity中有一个成员为Window，其实例化对象为PhoneWindow，PhoneWindow为抽象Window类的实现类。

Window是一个抽象类，提供了绘制窗口的一组通用API。
PhoneWindow是Window的具体继承实现类。而且该类内部包含了一个DecorView对象，该DecorView对象是所有应用窗口(Activity界面)的根View。
DecorView是PhoneWindow的内部类，是FrameLayout的子类，是对FrameLayout进行功能的修饰（所以叫DecorXXX），是所有应用窗口的根View

Activity、View、Window关系

一句话概括，Activity像工匠，View像窗花，window像窗户，LayoutInflater像剪刀，Xml像窗花图纸。Activity根据他们不同职能，并且与他们相互配合像我们展示灵活与精致的界面

View如何与Activity进行关联

View并不是直接与Activity关联，而是通过Window这个中间人，Window才是直接关联到Activity上的

Window如何与Activity进行关联

每一个Activity包含一个PhoneWindow，并且PhoneWindow是抽象类Window的子类，setContentView让View与Window关联，Activity与Window关联

总结

Activity包含一个PhoneWindow，而PhoneWindow继承Window，Activity通过setContentView将View设置到PhoneWindow上，而View通过WindowManager的addView，removeView，updateView来对View进行管理，Window的添加过程与Activity启动流程都是一个IPC过程。Activity启动完需要通过AMS完成，而Window添加过程需要通过WindowSession完成。

Activity 视图附加到Window上

通过Activity的setContentView方法来实现

//FEATURE_CONTENT_TRANSITIONS 转场动画
setContentView(R.layout.activity_test_event);

最后调用的是Activity的setContentView方法

public void setContentView(@LayoutRes int layoutResID) {
    getWindow().setContentView(layoutResID);
    initWindowDecorActionBar();
}

getWindow返回的是window对象，而window是抽象方法由PhoneWindow实现，所以调用是PhoneWindow的setContentView方法

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.
//判断mContentParent是否为空，这里它是一个viewgroup
    if (mContentParent == null) {
//为空，进行初始化操作
        installDecor();
    } else if (!hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
//不为空，移除之前所以的子view
        mContentParent.removeAllViews();
    }
//判断是否含有转场动画
    if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
        final Scene newScene = Scene.getSceneForLayout(mContentParent, layoutResID,
                getContext());
        transitionTo(newScene);
    } else {
//没有使用此方法加载布局，将布局加载到mContentParent中
        mLayoutInflater.inflate(layoutResID, mContentParent);
    }
    mContentParent.requestApplyInsets();
    final Callback cb = getCallback();
    if (cb != null &amp;&amp; !isDestroyed()) {
        cb.onContentChanged();
    }
    mContentParentExplicitlySet = true;
}
private void installDecor() {
    mForceDecorInstall = false;
//DecorView为空进行初始化
    if (mDecor == null) {
        mDecor = generateDecor(-1);
        mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);
        mDecor.setIsRootNamespace(true);
        if (!mInvalidatePanelMenuPosted &amp;&amp; mInvalidatePanelMenuFeatures != 0) {
            mDecor.postOnAnimation(mInvalidatePanelMenuRunnable);
        }
    } else {
//不为空，与PhoneWindow进行关联
        mDecor.setWindow(this);
    }
    if (mContentParent == null) {
//初始化操作，方法内部通过findviewbyid寻找是否存在id为content的Android内部布局FragmentLayout，有返回，
//没有抛异常
        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);
 
        if (decorContentParent != null) {
            mDecorContentParent = decorContentParent;
            mDecorContentParent.setWindowCallback(getCallback());
            if (mDecorContentParent.getTitle() == null) {
                mDecorContentParent.setWindowTitle(mTitle);
            }
 
            final int localFeatures = getLocalFeatures();
            for (int i = 0; i &lt; FEATURE_MAX; i++) {
                if ((localFeatures &amp; (1 &lt;&lt; i)) != 0) {
                    mDecorContentParent.initFeature(i);
                }
            }
 
            mDecorContentParent.setUiOptions(mUiOptions);
 
            if ((mResourcesSetFlags &amp; FLAG_RESOURCE_SET_ICON) != 0 ||
                    (mIconRes != 0 &amp;&amp; !mDecorContentParent.hasIcon())) {
                mDecorContentParent.setIcon(mIconRes);
            } else if ((mResourcesSetFlags &amp; FLAG_RESOURCE_SET_ICON) == 0 &amp;&amp;
                    mIconRes == 0 &amp;&amp; !mDecorContentParent.hasIcon()) {
                mDecorContentParent.setIcon(
                        getContext().getPackageManager().getDefaultActivityIcon());
                mResourcesSetFlags |= FLAG_RESOURCE_SET_ICON_FALLBACK;
            }
            if ((mResourcesSetFlags &amp; FLAG_RESOURCE_SET_LOGO) != 0 ||
                    (mLogoRes != 0 &amp;&amp; !mDecorContentParent.hasLogo())) {
                mDecorContentParent.setLogo(mLogoRes);
            }
            PanelFeatureState st = getPanelState(FEATURE_OPTIONS_PANEL, false);
            if (!isDestroyed() &amp;&amp; (st == null || st.menu == null) &amp;&amp; !mIsStartingWindow) {
                invalidatePanelMenu(FEATURE_ACTION_BAR);
            }
        } else {
            mTitleView = findViewById(R.id.title);
            if (mTitleView != null) {
                if ((getLocalFeatures() &amp; (1 &lt;&lt; FEATURE_NO_TITLE)) != 0) {
                    final View titleContainer = findViewById(R.id.title_container);
                    if (titleContainer != null) {
                        titleContainer.setVisibility(View.GONE);
                    } else {
                        mTitleView.setVisibility(View.GONE);
                    }
                    mContentParent.setForeground(null);
                } else {
                    mTitleView.setText(mTitle);
                }
            }
        }
 
        if (mDecor.getBackground() == null &amp;&amp; mBackgroundFallbackResource != 0) {
            mDecor.setBackgroundFallback(mBackgroundFallbackResource);
        }
 
        // Only inflate or create a new TransitionManager if the caller hasn&#039;t
        // already set a custom one.
        if (hasFeature(FEATURE_ACTIVITY_TRANSITIONS)) {
//有转场动画就加载动画资源
            if (mTransitionManager == null) {
                final int transitionRes = getWindowStyle().getResourceId(
                        R.styleable.Window_windowContentTransitionManager,
                        0);
                if (transitionRes != 0) {
                    final TransitionInflater inflater = TransitionInflater.from(getContext());
                    mTransitionManager = inflater.inflateTransitionManager(transitionRes,
                            mContentParent);
                } else {
                    mTransitionManager = new TransitionManager();
                }
            }
 
            mEnterTransition = getTransition(mEnterTransition, null,
                    R.styleable.Window_windowEnterTransition);
            mReturnTransition = getTransition(mReturnTransition, USE_DEFAULT_TRANSITION,
                    R.styleable.Window_windowReturnTransition);
            mExitTransition = getTransition(mExitTransition, null,
                    R.styleable.Window_windowExitTransition);
            mReenterTransition = getTransition(mReenterTransition, USE_DEFAULT_TRANSITION,
                    R.styleable.Window_windowReenterTransition);
            mSharedElementEnterTransition = getTransition(mSharedElementEnterTransition, null,
                    R.styleable.Window_windowSharedElementEnterTransition);
            mSharedElementReturnTransition = getTransition(mSharedElementReturnTransition,
                    USE_DEFAULT_TRANSITION,
                    R.styleable.Window_windowSharedElementReturnTransition);
            mSharedElementExitTransition = getTransition(mSharedElementExitTransition, null,
                    R.styleable.Window_windowSharedElementExitTransition);
            mSharedElementReenterTransition = getTransition(mSharedElementReenterTransition,
                    USE_DEFAULT_TRANSITION,
                    R.styleable.Window_windowSharedElementReenterTransition);
            if (mAllowEnterTransitionOverlap == null) {
                mAllowEnterTransitionOverlap = getWindowStyle().getBoolean(
                        R.styleable.Window_windowAllowEnterTransitionOverlap, true);
            }
            if (mAllowReturnTransitionOverlap == null) {
                mAllowReturnTransitionOverlap = getWindowStyle().getBoolean(
                        R.styleable.Window_windowAllowReturnTransitionOverlap, true);
            }
            if (mBackgroundFadeDurationMillis &lt; 0) {
                mBackgroundFadeDurationMillis = getWindowStyle().getInteger(
                        R.styleable.Window_windowTransitionBackgroundFadeDuration,
                        DEFAULT_BACKGROUND_FADE_DURATION_MS);
            }
            if (mSharedElementsUseOverlay == null) {
                mSharedElementsUseOverlay = getWindowStyle().getBoolean(
                        R.styleable.Window_windowSharedElementsUseOverlay, true);
            }
        }
    }
}

总结：

创建一个DecorView的mDecor对象，用于做为整个应用窗口的根视图；
将view添加到DecorView的mContentParent中；
依据Feature等style theme创建不同的窗口修饰布局文件，并且通过findViewById获取Activity布局文件该存放的地方（窗口修饰布局文件中id为content的FrameLayout)；
将Activity的布局文件添加至id为content的FrameLayout内；
回调Activity的onContentChanged方法通知Activity视图发生改变，onContentChanged是一个空的实现，可以自己在Activity中实现 final Callback cb = getCallback(); if (cb != null && !isDestroyed()) { cb.onContentChanged(); }

但是此时DecorView并没有被添加到WindowManager中，没有被识别，无法获取Window的具体功能，需要调用Activity中的makeVisible方法，DecorView才能真正的显示出来。最后Activity的Window就创建完成了。

 void makeVisible() {
        if (!mWindowAdded) {
            ViewManager wm = getWindowManager();
            wm.addView(mDecor, getWindow().getAttributes());
            mWindowAdded = true;
        }
        mDecor.setVisibility(View.VISIBLE);
    }

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原始发表：2019年9月18日，如有侵权请联系 cloudcommunity@tencent.com 删除

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