setContentView() 究竟都做了什么？

版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/crazy1235/article/details/72229175

---

转载请注明出处：http://blog.csdn.net/crazy1235/article/details/51471280

---

这个函数是在常见不过的了！

setContentView(R.layout.activity_test_view);

但是调用了这个函数设置Activity布局的时候，android系统究竟做了什么操作呢？

往下看！

---

setContentView()

我们新建项目模式都是使用的 Theme.AppCompat 主题，Activity都是继承于 AppCompatActivity 的！

OK，下面来一步步跟踪源码！

在AppCompatActivity中：

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

调用的是 getDelegate() 中对应的 setContentView() 函数。

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

AppCompatDelegate 及其子类

AppCompatDelegate 是 AppCompat代理类！

调用AppCompatDelegate中的静态方法create() ：

public static AppCompatDelegate create(Activity activity, AppCompatCallback callback) {
        return create(activity, activity.getWindow(), callback);
    }

接着又调用了另外一个重载的静态函数！

private static AppCompatDelegate create(Context context, Window window,
            AppCompatCallback callback) {
        final int sdk = Build.VERSION.SDK_INT;
        if (BuildCompat.isAtLeastN()) {
            return new AppCompatDelegateImplN(context, window, callback);
        } else if (sdk >= 23) {
            return new AppCompatDelegateImplV23(context, window, callback);
        } else if (sdk >= 14) {
            return new AppCompatDelegateImplV14(context, window, callback);
        } else if (sdk >= 11) {
            return new AppCompatDelegateImplV11(context, window, callback);
        } else {
            return new AppCompatDelegateImplV9(context, window, callback);
        }
    }

在这个函数里根据系统版本来创建不同的代理实现类！

通过查看这几个类的源码可以发现它们之间的继承关系如下图：

可以看出，setContentView() 方法实现是在 AppCompatDelegateImplV9 这个类中！

@Override
    public void setContentView(View v) {
        ensureSubDecor(); // 
        ViewGroup contentParent = (ViewGroup) mSubDecor.findViewById(android.R.id.content);
        contentParent.removeAllViews();
        contentParent.addView(v);
        mOriginalWindowCallback.onContentChanged();
    }

    @Override
    public void setContentView(int resId) {
        ensureSubDecor(); // 
        ViewGroup contentParent = (ViewGroup) mSubDecor.findViewById(android.R.id.content);
        contentParent.removeAllViews();
        LayoutInflater.from(mContext).inflate(resId, contentParent);
        mOriginalWindowCallback.onContentChanged();
    }

    @Override
    public void setContentView(View v, ViewGroup.LayoutParams lp) {
        ensureSubDecor(); // 
        ViewGroup contentParent = (ViewGroup) mSubDecor.findViewById(android.R.id.content);
        contentParent.removeAllViews();
        contentParent.addView(v, lp);
        mOriginalWindowCallback.onContentChanged();
    }

我们平时在Activity中主要用到的就是 public void setContentView(int resId) 这个函数！就那这个来说！

---

ensureSubDecor()

三个重载函数内部都是首先调用了 ensureSubDecor() 这个函数！

private void ensureSubDecor() {
        if (!mSubDecorInstalled) {
            mSubDecor = createSubDecor(); // !!!

            // If a title was set before we installed the decor, propagate it now
            CharSequence title = getTitle();
            if (!TextUtils.isEmpty(title)) {
                onTitleChanged(title);
            }

            applyFixedSizeWindow();

            onSubDecorInstalled(mSubDecor);

            mSubDecorInstalled = true;

            PanelFeatureState st = getPanelState(FEATURE_OPTIONS_PANEL, false);
            if (!isDestroyed() && (st == null || st.menu == null)) {
                invalidatePanelMenu(FEATURE_SUPPORT_ACTION_BAR);
            }
        }
    }

mSubDecorInstalled 默认是false，所以初次会调用 createSubDecor() 来创建 mSubDecor，实际上它就是一个ViewGroup！

private ViewGroup createSubDecor() {
        // [1]. 主题验证！
        TypedArray a = mContext.obtainStyledAttributes(R.styleable.AppCompatTheme);

        if (!a.hasValue(R.styleable.AppCompatTheme_windowActionBar)) {
            a.recycle();
            throw new IllegalStateException(
                    "You need to use a Theme.AppCompat theme (or descendant) with this activity.");
        }
        // [2]. 初始化相关特征标志！
        if (a.getBoolean(R.styleable.AppCompatTheme_windowNoTitle, false)) {
            requestWindowFeature(Window.FEATURE_NO_TITLE);
        } else if (a.getBoolean(R.styleable.AppCompatTheme_windowActionBar, false)) {
            requestWindowFeature(FEATURE_SUPPORT_ACTION_BAR);
        }
        if (a.getBoolean(R.styleable.AppCompatTheme_windowActionBarOverlay, false)) {
            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);
        a.recycle();

        // [3]. window对象创建decor view
        mWindow.getDecorView();

        final LayoutInflater inflater = LayoutInflater.from(mContext);
        ViewGroup subDecor = null; // subDecor是一个ViewGroup


        // [4]. 判断是否有title
        if (!mWindowNoTitle) {
            if (mIsFloating) {
                // (1)如果是浮动窗口形式 -- abc_dialog_title_material.xml
                subDecor = (ViewGroup) inflater.inflate(
                        R.layout.abc_dialog_title_material, null);

                // Floating windows 不允许有actionbar
                mHasActionBar = mOverlayActionBar = false;
            } else if (mHasActionBar) {
                TypedValue outValue = new TypedValue();
                mContext.getTheme().resolveAttribute(R.attr.actionBarTheme, outValue, true);

                Context themedContext;
                if (outValue.resourceId != 0) {
                    themedContext = new ContextThemeWrapper(mContext, outValue.resourceId);
                } else {
                    themedContext = mContext;
                }

                // (2) 费浮动窗口形式 -- abc_screen_toolbar.xml
                subDecor = (ViewGroup) LayoutInflater.from(themedContext)
                        .inflate(R.layout.abc_screen_toolbar, null);

                mDecorContentParent = (DecorContentParent) subDecor
                        .findViewById(R.id.decor_content_parent);
                mDecorContentParent.setWindowCallback(getWindowCallback());

                // ... 省略代码
                }
            }
        } else {
            // (3) abc_screen_simple_overlay_action_mode.xml
            if (mOverlayActionMode) {
                subDecor = (ViewGroup) inflater.inflate(
                        R.layout.abc_screen_simple_overlay_action_mode, null);
            } else {
                // (4) abc_screen_simple.xml
                subDecor = (ViewGroup) inflater.inflate(R.layout.abc_screen_simple, null);
            }

            // ... 省略代码

        // [5]. 如果此时subDecor为空，则抛异常~
        if (subDecor == null) {
            throw new IllegalArgumentException(
                    "AppCompat does not support the current theme features: { "
                            + "windowActionBar: " + mHasActionBar
                            + ", windowActionBarOverlay: "+ mOverlayActionBar
                            + ", android:windowIsFloating: " + mIsFloating
                            + ", windowActionModeOverlay: " + mOverlayActionMode
                            + ", windowNoTitle: " + mWindowNoTitle
                            + " }");
        }

        if (mDecorContentParent == null) {
            mTitleView = (TextView) subDecor.findViewById(R.id.title);
        }

        // Make the decor optionally fit system windows, like the window's decor
        ViewUtils.makeOptionalFitsSystemWindows(subDecor);


        // [6]. 获取ContentFrameLayout
        final ContentFrameLayout contentView = (ContentFrameLayout) subDecor.findViewById(
                R.id.action_bar_activity_content);

        // [7]. 获取PhoneWindow中的content布局对象
        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
            while (windowContentView.getChildCount() > 0) {
                final View child = windowContentView.getChildAt(0);
                windowContentView.removeViewAt(0);
                contentView.addView(child);
            }

            // [8]. 将contentView的id更改为android.R.id.content
            windowContentView.setId(View.NO_ID);
            contentView.setId(android.R.id.content);

            // The decorContent may have a foreground drawable set (windowContentOverlay).
            // Remove this as we handle it ourselves
            if (windowContentView instanceof FrameLayout) {
                ((FrameLayout) windowContentView).setForeground(null);
            }
        }

        // [9]. 对PhoneWindow设置ContentView
        mWindow.setContentView(subDecor);

        // [10]. 设置attach监听
        contentView.setAttachListener(new ContentFrameLayout.OnAttachListener() {
            @Override
            public void onAttachedFromWindow() {}

            @Override
            public void onDetachedFromWindow() {
                dismissPopups();
            }
        });

        return subDecor;
    }

方法体里面步骤标注的比较详细了。

下面针对关键的几步详细说一下！

---

requestWindowFeature

@Override
    public boolean requestWindowFeature(int featureId) {
        featureId = sanitizeWindowFeatureId(featureId);

        if (mWindowNoTitle && featureId == FEATURE_SUPPORT_ACTION_BAR) {
            return false; // Ignore. No title dominates.
        }
        if (mHasActionBar && featureId == Window.FEATURE_NO_TITLE) {
            // Remove the action bar feature if we have no title. No title dominates.
            mHasActionBar = false;
        }

        switch (featureId) {
            case FEATURE_SUPPORT_ACTION_BAR:
                throwFeatureRequestIfSubDecorInstalled();
                mHasActionBar = true;
                return true;
            case FEATURE_SUPPORT_ACTION_BAR_OVERLAY:
                throwFeatureRequestIfSubDecorInstalled();
                mOverlayActionBar = true;
                return true;
            case FEATURE_ACTION_MODE_OVERLAY:
                throwFeatureRequestIfSubDecorInstalled();
                mOverlayActionMode = true;
                return true;
            case Window.FEATURE_PROGRESS:
                throwFeatureRequestIfSubDecorInstalled();
                mFeatureProgress = true;
                return true;
            case Window.FEATURE_INDETERMINATE_PROGRESS:
                throwFeatureRequestIfSubDecorInstalled();
                mFeatureIndeterminateProgress = true;
                return true;
            case Window.FEATURE_NO_TITLE:
                throwFeatureRequestIfSubDecorInstalled();
                mWindowNoTitle = true;
                return true;
        }

        return mWindow.requestFeature(featureId);
    }

从这个方法可以看出，我们在Activity里面调用requestWindowFeature(xxx)，实际上就是设定了先关参数的状态（布尔值）！

但是每个case语句首先都调用了 throwFeatureRequestIfSubDecorInstalled() ；

private void throwFeatureRequestIfSubDecorInstalled() {
        if (mSubDecorInstalled) {
            throw new AndroidRuntimeException(
                    "Window feature must be requested before adding content");
        }
    }

上面提到 mSubDecorInstalled 这个标志初始为false，在我们调用setContentView()的函数内部 变成了true。

所以当在 setContentView() 方法后面再次调用 requestWindowFeature(xxx) 时，就会抛出运行时异常！

所以说在Activity中onCreate() 函数中，requestWindowFeature() 要写在setContentView() 的前面！

---

mWindow.getDecorView()

mWindow是一个Window对象，Window是一个抽象类，实现子类是 PhoneWindow 。

该mWindow对象是从activity中获得的！

public static AppCompatDelegate create(Activity activity, AppCompatCallback callback) {
        return create(activity, activity.getWindow(), callback);
    }

那么具体PhoneWindow的创建这里先不谈！

直接看PhoneWindow中的先关函数：

@Override
    public final View getDecorView() {
        if (mDecor == null || mForceDecorInstall) {
            installDecor();
        }
        return mDecor;
    }

mDecor 是一个 DecorView 对象。

private void installDecor() {
        mForceDecorInstall = false;
        if (mDecor == null) {
            mDecor = generateDecor(-1); // [1]. 创建decorView对象
            // ... 省略代码
        } else {
            mDecor.setWindow(this);
        }
        if (mContentParent == null) {
            mContentParent = generateLayout(mDecor); // [2]. 
            // ... 省略代码
        }
    }

installDecor() 方法体内部主要的函数是上面标注出来的那两行！

protected DecorView generateDecor(int featureId) {
        // ...省略
        return new DecorView(context, featureId, this, getAttributes());
    }

generateDecor() 方法体很简单，直接创建了一个DecorView对象返回！

protected ViewGroup generateLayout(DecorView decor) {
        // Apply data from current theme.

        TypedArray a = getWindowStyle();

        // [1]. 读取属性设置标志和状态

        mIsFloating = a.getBoolean(R.styleable.Window_windowIsFloating, false);
        int flagsToUpdate = (FLAG_LAYOUT_IN_SCREEN|FLAG_LAYOUT_INSET_DECOR)
                & (~getForcedWindowFlags());
        if (mIsFloating) {
            setLayout(WRAP_CONTENT, WRAP_CONTENT);
            setFlags(0, flagsToUpdate);
        } else {
            setFlags(FLAG_LAYOUT_IN_SCREEN|FLAG_LAYOUT_INSET_DECOR, flagsToUpdate);
        }

        if (a.getBoolean(R.styleable.Window_windowNoTitle, false)) {
            requestFeature(FEATURE_NO_TITLE);
        } else if (a.getBoolean(R.styleable.Window_windowActionBar, false)) {
            // Don't allow an action bar if there is no title.
            requestFeature(FEATURE_ACTION_BAR);
        }

        // ... 省略代码 

        // [2]. 映射decor布局

        int layoutResource;
        int features = getLocalFeatures();

        if ((features & (1 << FEATURE_SWIPE_TO_DISMISS)) != 0) {
             // (1)screen_swipe_dismiss.xml
            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);
                // (2) dialog_title_icons.xml
                layoutResource = res.resourceId; 
            } else {
                // (3) screen_title_icons.xml
                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) {
            // (4) screen_progress.xml
            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);
                // (5). dialog_custom_title.xml
                layoutResource = res.resourceId; 
            } else {
                // (6). screen_custom_title.xml
                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);
                // (7). dialog_title.xml
                layoutResource = res.resourceId; 
            } else if ((features & (1 << FEATURE_ACTION_BAR)) != 0) {
                // (8). screen_action_bar.xml
                layoutResource = a.getResourceId(
                        R.styleable.Window_windowActionBarFullscreenDecorLayout,
                        R.layout.screen_action_bar); 
            } else {
                // (9). screen_title.xml
                layoutResource = R.layout.screen_title;
            }
        } else if ((features & (1 << FEATURE_ACTION_MODE_OVERLAY)) != 0) {
            // (10). screen_simple_overlay_action_mode.xml
            layoutResource = R.layout.screen_simple_overlay_action_mode; 
        } else {
            // (11). screen_simple.xml
            layoutResource = R.layout.screen_simple; 
        }

        // [3]. 开始更新decor -- mChanging = true;
        mDecor.startChanging();
        // [4]. 加载 layoutResourc 放到 decor 中
        mDecor.onResourcesLoaded(mLayoutInflater, layoutResource);

        // [5]. 找到 【com.android.internal.R.id.content】 对应的View
        ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);
        if (contentParent == null) {
            throw new RuntimeException("Window couldn't find content container view");
        }

        // ...

        // 设置背景，title，titleColor等属性

        // [6]. 结束更新decor -- mChanging = false;
        mDecor.finishChanging();

        return contentParent;
    }

在 generateLayout() 函数内部，根据features 等一些列参数判断，一共有11种布局！

• screen_swipe_dismiss.xml

• dialog_title_icons.xml

• screen_title_icons.xml

• screen_progress.xml

• dialog_custom_title.xml

• screen_custom_title.xml

• dialog_title.xml

• screen_action_bar.xml

• screen_title.xml

• screen_simple_overlay_action_mode.xml

• screen_simple.xml

但是不管是哪个布局，里面都有一个id是 @android:id/content 的控件！

---

DecorView.onResourcesLoaded()

mDecor.onResourcesLoaded(mLayoutInflater, layoutResource);

将上一步得到的布局映射出来添加到mDecor 这个ViewGroup 中！

void onResourcesLoaded(LayoutInflater inflater, int layoutResource) {
        mStackId = getStackId();

        // ... 省略代码

        mDecorCaptionView = createDecorCaptionView(inflater);
        final View root = inflater.inflate(layoutResource, null);
        if (mDecorCaptionView != null) {
            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();
    }

从上面代码块看出，addView() 函数将layoutResource映射出来的布局添加到DecorView中！并且宽高参数都是 MATCH_PARENT !

---

OK，再接着上面的createSubDecor() 往下分析。

        // [3]. window对象创建decor view
        mWindow.getDecorView();

        final LayoutInflater inflater = LayoutInflater.from(mContext);
        ViewGroup subDecor = null; // subDecor是一个ViewGroup

此时window的decor view创建完毕！

接下来映射 subDecor 布局根据不同情况也对应了下面4种布局：

• abc_dialog_title_material.xml

• abc_screen_toolbar.xml

• abc_screen_simple_overlay_action_mode.xml

• abc_screen_simple

但是无论哪种布局，里面都 include 一个 abc_screen_content_include.xml 布局

<merge xmlns:android="http://schemas.android.com/apk/res/android">

    <android.support.v7.widget.ContentFrameLayout
            android:id="@id/action_bar_activity_content"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:foregroundGravity="fill_horizontal|top"
            android:foreground="?android:attr/windowContentOverlay" />

</merge>

final ContentFrameLayout contentView = (ContentFrameLayout) subDecor.findViewById(
                R.id.action_bar_activity_content);

final ViewGroup windowContentView = (ViewGroup) mWindow.findViewById(android.R.id.content);

所以contentView 就是这个ContentFrameLayout布局！

windowContentView 是 我们上面提到的android.R.id.content对应的布局！

由于那11中布局中android.R.id.content对应的布局不同，所以这里使用 ViewGroup 进行转化!

windowContentView.setId(View.NO_ID);
contentView.setId(android.R.id.content);

接着讲decorView中的 android.R.id.content 对应的控件id 设置为 View.NO_ID

将 subDecor 中 R.id.action_bar_activity_content 对应的布局 ID 设置为 android.R.id.content

---

PhoneWindow.setContentView()

最后是 mWindow.setContentView(subDecor);

在PhoneWindow中有三个setContentView() 重载函数！

@Override
    public void setContentView(int layoutResID) {
        // ... 
    }

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

    @Override
    public void setContentView(View view, ViewGroup.LayoutParams params) {
         // ... 
    }

我们只来关注第三个。

@Override
    public void setContentView(View view, ViewGroup.LayoutParams params) {
        // mContentParent !!! 注意这个变量
        if (mContentParent == null) {
            installDecor();
        } else if (!hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
            mContentParent.removeAllViews();
        }
        // 是否需要transition动画
        if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
            view.setLayoutParams(params);
            final Scene newScene = new Scene(mContentParent, view);
            transitionTo(newScene);
        } else {
            mContentParent.addView(view, params);
        }
        mContentParent.requestApplyInsets();
        final Callback cb = getCallback();
        if (cb != null && !isDestroyed()) {
            cb.onContentChanged();
        }
        mContentParentExplicitlySet = true;
    }

当有过度场景动画时，view的添加实在Scene进入的时候！

Scene.java

 public void enter() {

        // Apply layout change, if any
        if (mLayoutId > 0 || mLayout != null) {
            // empty out parent container before adding to it
            getSceneRoot().removeAllViews();

            if (mLayoutId > 0) {
                LayoutInflater.from(mContext).inflate(mLayoutId, mSceneRoot);
            } else {
                mSceneRoot.addView(mLayout); 
            }
        }

        // ... 
    }

mSceneRoot 就是上面构造Scene传入的 mContentParent , mLayout 是构造Scene传入的view, 也就是 AppCompatDelegateImplV9 里面的 subDecor

当没有过度动画，直接将subDecor添加到mContentParent 中！

而 mContentParent 是谁呢？？？

它就是PhonWindow 类中 installDecor() 函数中，通过 generateLayout(mDecor) 生成的ViewGroup！

在 generateLayout() 函数体内：

ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);

public static final int ID_ANDROID_CONTENT = com.android.internal.R.id.content;

OK。这个conetentParent就是 R.id.content对应的布局！

也就是说 mContentParent 就是 R.id.content对应的布局！

所以，mWindow.setContentView(subDecor); 就是把subDecor添加到了R.id.content 的布局中了！

而此时添加完毕之后，R.id.content对应的布局就变成了 subDecor里面的 原 R.id.action_bar_activity_content 对应的 ContentFrameLayout 布局！

---

至此， ensureSubDecor() 的过程分析完毕！

在回过头看AppCompatDelegateImplV9.java 中的 setContentView() 函数！

ViewGroup contentParent = (ViewGroup) mSubDecor.findViewById(android.R.id.content);
contentParent.removeAllViews();
contentParent.addView(v, lp);

此时就可看出，我们在Activity中调用setContentView（xxx），就是把布局添加到了android.R.id.content对应的布局中。

---

ContentFrameLayout就是ID被更改为android.R.id.content的布局！也是我们在activity中设置布局的父布局！