1、 Window

window 位于 android.view.Window.java。
我们来看下源码里面的说明

/**
 * 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 {
    ...
    @Nullable
    public View findViewById(@IdRes int id) {
        return getDecorView().findViewById(id);
    }

/**
 * Convenience for * {@link #setContentView(View, android.view.ViewGroup.LayoutParams)}
 * to set the screen content from a layout resource.  The resource will be * inflated, adding all top-level views to the screen. * * @param layoutResID Resource ID to be inflated.
 * @see #setContentView(View, android.view.ViewGroup.LayoutParams)
 */
     public abstract void setContentView(@LayoutRes int layoutResID);
     ...
}

该类是一个抽象类，提供了绘制窗口的一组通用API。可以将之理解为一个载体，各种View在这个载体上显示。每一个Activity都包含一个Window对象

2、 PhoneWindow

PhoneWindow位于com.android.internal.policy.PhoneWindow.java。

public class PhoneWindow extends Window implements MenuBuilder.Callback {

    private final static String TAG = "PhoneWindow";

    ...

    // This is the top-level view of the window, containing the window decor.
    private DecorView mDecor;

    // 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.
    private ViewGroup mContentParent;

    private ViewGroup mContentRoot;

    @Override
    public final View getDecorView() {
        if (mDecor == null || mForceDecorInstall) {
            installDecor();
        }
        return mDecor;
    }
    private void installDecor() {
        //mDecor是DecorView,第一次mDecor=null，所以调用generateDecor
        if (mDecor == null) {
            mDecor = generateDecor();
               ...
         }
         //第一次mContentParent也等于null
        if (mContentParent == null) {
            //可以看到把DecorView传入进去了
            mContentParent = generateLayout(mDecor);
        }

    }
    ...
}

该类继承于Window类，是Window类的具体实现，我们可以通过该类具体去绘制窗口。该类内部包含了一个DecorView对象，该DectorView对象是所有应用窗口(Activity界面)的根View。 PhoneWindow类是把一个DecorView(FrameLayout)对象进行一定的包装，并提供一组通用的窗口操作接口。

3、 DecorView

 private final class DecorView extends FrameLayout implements RootViewSurfaceTaker {

        /* package */int mDefaultOpacity = PixelFormat.OPAQUE;

        /** The feature ID of the panel, or -1 if this is the application's DecorView */
        private final int mFeatureId;

        private final Rect mDrawingBounds = new Rect();

        private final Rect mBackgroundPadding = new Rect();

        private final Rect mFramePadding = new Rect();

        private final Rect mFrameOffsets = new Rect();
        ....
 }

继承自FrameLayout，该类就是对普通的FrameLayout进行功能的扩展，更确切点可以说是修饰(Decor的英文全称是Decoration，即“修饰”的意思)，比如说添加TitleBar(标题栏)。最重要的一点是，它是所有应用窗口的根View 。

4、 AppCompatActivity.setContentView源码流程

compileSdkVersion 27 本版本以下源码是基于sdk 27 分析的，不同版本有不同

点击 AppCompatActivity.setContentView();方法

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

    /**
     * @return The {@link AppCompatDelegate} being used by this Activity.
     */
    @NonNull
    public AppCompatDelegate getDelegate() {
        if (mDelegate == null) {
            mDelegate = AppCompatDelegate.create(this, this);
        }
        return mDelegate;
    }

点击AppCompatDelegate.create

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

    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 {
            return new AppCompatDelegateImplV14(context, window, callback);
        }
    }

重点来了

AppCompatDelegateImplN extends AppCompatDelegateImplV23
AppCompatDelegateImplV23 extends AppCompatDelegateImplV14
AppCompatDelegateImplV14 extends AppCompatDelegateImplV9

AppCompatDelegateImplV9 的部分源码

    @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();
    }

我们自己的view 被添加到content 里面了，

    private void ensureSubDecor() {
        if (!mSubDecorInstalled) {
            
            //这个mSubDecor其实就ViewGroup,调用createSubDecor()后，此时存放我们的布局的容器已经准备好了
            mSubDecor = createSubDecor();//核心代码！
           .....
    }

调用了createSubDecor()，看字面意思创建了一个SubDecor,看似跟DecorView有联系。我们看下里面做了什么操作

    private ViewGroup createSubDecor() {
        TypedArray a = mContext.obtainStyledAttributes(R.styleable.AppCompatTheme);

        if (!a.hasValue(R.styleable.AppCompatTheme_windowActionBar)) {
            a.recycle();
            //还记得我们使用AppCompatActivity如果不设置AppCompat主题报的错误吗？就是在这里抛出来的
            throw new IllegalStateException(
                    "You need to use a Theme.AppCompat theme (or descendant) with this activity.");
        }
        //初始化相关特征标志
        if (a.getBoolean(R.styleable.AppCompatTheme_windowNoTitle, false)) {
            //一般我们的主题默认都是NoTitle
            requestWindowFeature(Window.FEATURE_NO_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);
        }
        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();

        //重点！在这里就创建DecorView,至于DecorView到底是什么以及如何创建的，稍后会讲到
        mWindow.getDecorView();

        final LayoutInflater inflater = LayoutInflater.from(mContext);
        //可以看到其实就是个ViewGroup，我们接着往下看，跟DecorView到底有啥关系
        ViewGroup subDecor = null;


        if (!mWindowNoTitle) {
            //上面说了主题默认都是NoTitle，所以不会走里面的方法
            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) {
                
                TypedValue outValue = new TypedValue();
                mContext.getTheme().resolveAttribute(R.attr.actionBarTheme, outValue, true);

                ...

                // 重点---------------->1
                subDecor = (ViewGroup) LayoutInflater.from(themedContext)
                        .inflate(R.layout.abc_screen_toolbar, null);

                /**
                 * Propagate features to DecorContentParent
                 */
                if (mOverlayActionBar) {
                    mDecorContentParent.initFeature(FEATURE_SUPPORT_ACTION_BAR_OVERLAY);
                }
                if (mFeatureProgress) {
                    mDecorContentParent.initFeature(Window.FEATURE_PROGRESS);
                }
                if (mFeatureIndeterminateProgress) {
                    mDecorContentParent.initFeature(Window.FEATURE_INDETERMINATE_PROGRESS);
                }
            }
        } else {
            //我们进入else
            if (mOverlayActionMode) {
                //调用了requestWindowFeature(FEATURE_ACTION_MODE_OVERLAY)会走进来
              // 重点---------------->2
                subDecor = (ViewGroup) inflater.inflate(
                        R.layout.abc_screen_simple_overlay_action_mode, null);
            } else {
                //ok，所以如果这些我们都没设置，默认就走到这里来了，在这里映射出了subDecor,稍后我们来看下这个布局是啥
               // 重点---------------->3
                subDecor = (ViewGroup) inflater.inflate(R.layout.abc_screen_simple, null);
            }

            ...
        }

        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);
        //这个contentView很重要，是我们布局的父容器，你可以把它直接当成FrameLayout
         // 重点---------------->4
        final ContentFrameLayout contentView = (ContentFrameLayout) subDecor.findViewById(
                R.id.action_bar_activity_content);
        //看过相关知识的同学应该知道android.R.id.content这个Id在以前是我们布局的父容器的Id
          // 重点---------------->5
        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);
            }

            //注意！原来windowContentView的Id是android.R.id.content，现在设置成NO_ID
            // 重点---------------->6
            windowContentView.setId(View.NO_ID);
            //在之前这个id是我们的父容器，现在将contentView设置成android.R.id.content，那么可以初步判定，这个contentView将会是我的父容器
            // 重点---------------->7
            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);
            }
        }

        // Now set the Window's content view with the decor
        //注意！重要！将subDecor放入到了这个Window里面，这个Window是个抽象类，其实现类是PhoneWindow，稍后会讲到
        mWindow.setContentView(subDecor);

        ....

        return subDecor;
    }

我们来看下这个abc_screen_simple.xml的布局到底是什么样子的

<android.support.v7.internal.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.internal.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.internal.widget.FitWindowsLinearLayout

abc_screen_content_include.xml

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

    <android.support.v7.internal.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>

原来这个subDecor就是FitWindowsLinearLayout

非常重要的两行代码

mWindow.getDecorView();
mWindow.setContentView(subDecor);

而 mWindow 是 activity.getWindow() 获取到的
我们打开 activity源码

  mWindow = new PhoneWindow(this, window, activityConfigCallback);

发现 这里的window 就是PhoneWindow
在generateDecor()做了什么？其实返回了一个DecorView对象。

protected DecorView generateDecor(int featureId) {
        // System process doesn't have application context and in that case we need to directly use
        // the context we have. Otherwise we want the application context, so we don't cling to the
        // activity.
        Context context;
        if (mUseDecorContext) {
            Context applicationContext = getContext().getApplicationContext();
            if (applicationContext == null) {
                context = getContext();
            } else {
                context = new DecorContext(applicationContext, getContext().getResources());
                if (mTheme != -1) {
                    context.setTheme(mTheme);
                }
            }
        } else {
            context = getContext();
        }
        return new DecorView(context, featureId, this, getAttributes());
    }

我们在来看看generateLayout()做了什么。

protected ViewGroup generateLayout(DecorView decor) {
        TypedArray a = getWindowStyle();
        //设置一堆标志位...
        ...
        if (!mForcedStatusBarColor) {
            //获取主题状态栏的颜色
            mStatusBarColor = a.getColor(R.styleable.Window_statusBarColor, 0xFF000000);
        }
        if (!mForcedNavigationBarColor) {
            //获取底部NavigationBar颜色
            mNavigationBarColor = a.getColor(R.styleable.Window_navigationBarColor, 0xFF000000);
        }

        //获取主题一些资源
       ...

        // Inflate the window decor.

        int layoutResource;
        int features = getLocalFeatures();
        // System.out.println("Features: 0x" + Integer.toHexString(features));
        if ((features & (1 << FEATURE_SWIPE_TO_DISMISS)) != 0) {
            ...我们设置不同的主题以及样式，会采用不同的布局文件...
        } else {
            //记住这个布局，之后我们会来验证下布局的结构
            layoutResource = R.layout.screen_simple;
            // System.out.println("Simple!");
        }
        //要开始更改mDecor啦~
        mDecor.startChanging();
        //注意，此时把screen_simple放到了DecorView里面
       // 重点---------1
        mDecor.onResourcesLoaded(mLayoutInflater, layoutResource);
        //这里的ID_ANDROID_CONTENT就是R.id.content;
        ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);
        if (contentParent == null) {
            throw new RuntimeException("Window couldn't find content container view");
        }

        ...
        
        
        //这里的getContainer()返回的是个Window类，也就是父Window，一般为空
        if (getContainer() == null) {
            final Drawable background;
            if (mBackgroundResource != 0) {
                background = getContext().getDrawable(mBackgroundResource);
            } else {
                background = mBackgroundDrawable;
            }
            //设置背景
            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;
    }

我们来看看这个screen_simple.xml布局是什么样子的

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    android:orientation="vertical">
    <ViewStub android:id="@+id/action_mode_bar_stub"
              android:inflatedId="@+id/action_mode_bar"
              android:layout="@layout/action_mode_bar"
              android:layout_width="match_parent"
              android:layout_height="wrap_content" />
    <FrameLayout
         android:id="@android:id/content"
         android:layout_width="match_parent"
         android:layout_height="match_parent"
         android:foregroundInsidePadding="false"
         android:foregroundGravity="fill_horizontal|top"
         android:foreground="?android:attr/windowContentOverlay" />
</LinearLayout>

打开 DecorView 的onResourcesLoaded

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

        if (mBackdropFrameRenderer != null) {
            loadBackgroundDrawablesIfNeeded();
            mBackdropFrameRenderer.onResourcesLoaded(
                    this, mResizingBackgroundDrawable, mCaptionBackgroundDrawable,
                    mUserCaptionBackgroundDrawable, getCurrentColor(mStatusColorViewState),
                    getCurrentColor(mNavigationColorViewState));
        }

        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();
    }

此时 screen_simple.xml 添加到 DecorView 里面了
再来看看 mWindow.setContentView(subDecor);

    @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) {
            installDecor();
        } else if (!hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
            mContentParent.removeAllViews();
        }

        if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
            final Scene newScene = Scene.getSceneForLayout(mContentParent, layoutResID,
                    getContext());
            transitionTo(newScene);
        } else {
            mLayoutInflater.inflate(layoutResID, mContentParent);
        }
        mContentParent.requestApplyInsets();
        final Callback cb = getCallback();
        if (cb != null && !isDestroyed()) {
            cb.onContentChanged();
        }
        mContentParentExplicitlySet = true;
    }

上面说到了 subDecor就是FitWindowsLinearLayout
此时将 FitWindowsLinearLayout 添加到mContentParent了

我们看看 mContentParent 是个什么东西

private void installDecor() {
        mForceDecorInstall = false;
        if (mDecor == null) {
            mDecor = generateDecor(-1);
            mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);
            mDecor.setIsRootNamespace(true);
            if (!mInvalidatePanelMenuPosted && mInvalidatePanelMenuFeatures != 0) {
                mDecor.postOnAnimation(mInvalidatePanelMenuRunnable);
            }
        } else {
            mDecor.setWindow(this);
        }
        if (mContentParent == null) {
            mContentParent = generateLayout(mDecor);
  }

protected ViewGroup generateLayout(DecorView decor) {
ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);
 return contentParent;
}

可以发现contentParent 就是
screen_simple.xml 重的Framelayout

5校验、

ViewGroup decor = (ViewGroup) getWindow().getDecorView();
View decorChild  = decor.findViewById(android.R.id.content);
while (decorChild.getParent() != decor){
      decorChild = (View) decorChild.getParent();
      AppLog.e(decorChild.getClass());
 }

AppLog: class android.support.v7.widget.FitWindowsLinearLayout
AppLog: class android.widget.FrameLayout
AppLog: class android.widget.LinearLayout

层级.png

在Android studio的Tools–>Layout Inspector–>选中连接的手机–>打开你要看的应用，然后在屏幕上就会显示当前页面的布局结构图View Tree

WeChat2367739a22a041f02223e67e4276cb56.png

6、 Activity

AppLog: class android.widget.LinearLayout