Activity的setContentView的流程

最简单的Activity中的内容大致是这样的:

public class MainActivity extends Activity {  

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main_activity);
    }  

}  

setContentView

一般来说我们设置页面的内容视图是都是通过setContentView方法，那么我们就以2.3源码为例就来看看Activity中的setContentView到底做了什么吧。

 /**
  * Set the activity content from a layout resource.  The resource will be
  * inflated, adding all top-level views to the activity.
  *
  * @param layoutResID Resource ID to be inflated.
  */
 public void setContentView(int layoutResID) {
     getWindow().setContentView(layoutResID);
 }  

 public Window getWindow() {
     return mWindow;
 }  

 private Window mWindow;  

我们可以看到，实际上调用的mWindow的setContentView方法，在Android Touch事件分发过程这篇文章中我们已经指出Window的实现类为PhoneWindow类

 @Override
 public void setContentView(int layoutResID) {
     if (mContentParent == null) {
         installDecor();         // 1、生成DecorView
     } else {
         mContentParent.removeAllViews();
     }
     mLayoutInflater.inflate(layoutResID, mContentParent);// 2、将layoutResId的布局添加到mContentParent中
     final Callback cb = getCallback();
     if (cb != null) {
         cb.onContentChanged();
     }
 }
     // 构建mDecor对象,并且初始化标题栏和Content Parent(我们要显示的内容区域)
     private void installDecor() {
     if (mDecor == null) {
         mDecor = generateDecor();          // 3、构建DecorView
         mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);
         mDecor.setIsRootNamespace(true);
     }
     if (mContentParent == null) {
         mContentParent = generateLayout(mDecor);              // 4、获取ContentView容器，即显示内容的区域  

         mTitleView = (TextView)findViewById(com.android.internal.R.id.title); 、设置Title等
         if (mTitleView != null) {
             if ((getLocalFeatures() & ( << FEATURE_NO_TITLE)) != ) {
                 View titleContainer = findViewById(com.android.internal.R.id.title_container);
                 if (titleContainer != null) {
                     titleContainer.setVisibility(View.GONE);
                 } else {
                     mTitleView.setVisibility(View.GONE);
                 }
                 if (mContentParent instanceof FrameLayout) {
                     ((FrameLayout)mContentParent).setForeground(null);
                 }
             } else {
                 mTitleView.setText(mTitle);
             }
         }
     }
 }  

     protected DecorView generateDecor() {
     return new DecorView(getContext(), -);    // 构建mDecor对象
 }  

我们可以看到，setContentView的基本流程简单概括就是如下几步：

1、构建mDecor对象。mDecor就是整个窗口的顶层视图，它主要包含了Title和Content View两个区域 （参考图1中的两个区域 ），Title区域就是我们的标题栏，Content View区域就是显示我们xml布局内容中的区域。关于mDecor对象更多说明也请参考Android Touch事件分发过程这篇文章；

2、设置一些关于窗口的属性，初始化标题栏区域和内容显示区域；

这里比较复杂的就是generateLayout(mDecor)这个函数，我们一起来分析一下吧。

 // 返回用于显示我们设置的页面内容的ViewGroup容器
 protected ViewGroup generateLayout(DecorView decor) {
    // Apply data from current theme.
    // 1、获取窗口的Style属性
    TypedArray a = getWindowStyle();  

    if (false) {
        System.out.println("From style:");
        String s = "Attrs:";
        for (int i = ; i < com.android.internal.R.styleable.Window.length; i++) {
            s = s + " " + Integer.toHexString(com.android.internal.R.styleable.Window[i]) + "="
                    + a.getString(i);
        }
        System.out.println(s);
    }
    // 窗口是否是浮动的
    mIsFloating = a.getBoolean(com.android.internal.R.styleable.Window_windowIsFloating, false);
    int flagsToUpdate = (FLAG_LAYOUT_IN_SCREEN|FLAG_LAYOUT_INSET_DECOR)
            & (~getForcedWindowFlags());
    if (mIsFloating) {
        setLayout(WRAP_CONTENT, WRAP_CONTENT);
        setFlags(, flagsToUpdate);
    } else {
        setFlags(FLAG_LAYOUT_IN_SCREEN|FLAG_LAYOUT_INSET_DECOR, flagsToUpdate);
    }
    // 设置是否不显示title区域
    if (a.getBoolean(com.android.internal.R.styleable.Window_windowNoTitle, false)) {
        requestFeature(FEATURE_NO_TITLE);
    }
    // 设置全屏的flag
    if (a.getBoolean(com.android.internal.R.styleable.Window_windowFullscreen, false)) {
        setFlags(FLAG_FULLSCREEN, FLAG_FULLSCREEN&(~getForcedWindowFlags()));
    }  

    if (a.getBoolean(com.android.internal.R.styleable.Window_windowShowWallpaper, false)) {
        setFlags(FLAG_SHOW_WALLPAPER, FLAG_SHOW_WALLPAPER&(~getForcedWindowFlags()));
    }  

    WindowManager.LayoutParams params = getAttributes();
    // 设置输入法模式
    if (!hasSoftInputMode()) {
        params.softInputMode = a.getInt(
                com.android.internal.R.styleable.Window_windowSoftInputMode,
                params.softInputMode);
    }  

    if (a.getBoolean(com.android.internal.R.styleable.Window_backgroundDimEnabled,
            mIsFloating)) {
        /* All dialogs should have the window dimmed */
        if ((getForcedWindowFlags()&WindowManager.LayoutParams.FLAG_DIM_BEHIND) == ) {
            params.flags |= WindowManager.LayoutParams.FLAG_DIM_BEHIND;
        }
        params.dimAmount = a.getFloat(
                android.R.styleable.Window_backgroundDimAmount, 0.5f);
    }
    // 窗口动画
    if (params.windowAnimations == ) {
        params.windowAnimations = a.getResourceId(
                com.android.internal.R.styleable.Window_windowAnimationStyle, );
    }  

    // The rest are only done if this window is not embedded; otherwise,
    // the values are inherited from our container.
    if (getContainer() == null) {
        if (mBackgroundDrawable == null) {
            if (mBackgroundResource == ) {
                mBackgroundResource = a.getResourceId(
                        com.android.internal.R.styleable.Window_windowBackground, );
            }
            if (mFrameResource == ) {
                mFrameResource = a.getResourceId(com.android.internal.R.styleable.Window_windowFrame, );
            }
            if (false) {
                System.out.println("Background: "
                        + Integer.toHexString(mBackgroundResource) + " Frame: "
                        + Integer.toHexString(mFrameResource));
            }
        }
        mTextColor = a.getColor(com.android.internal.R.styleable.Window_textColor, 0xFF000000);
    }  

    // Inflate the window decor.
    // 2、根据一些属性来选择不同的顶层视图布局,例如设置了FEATURE_NO_TITLE的属性，那么就选择没有Title区域的那么布局；
    // layoutResource布局就是整个Activity的布局，其中含有title区域和content区域，content区域就是用来显示我通过
    // setContentView设置进来的内容区域，也就是我们要显示的视图。  

    int layoutResource;
    int features = getLocalFeatures();
    // System.out.println("Features: 0x" + Integer.toHexString(features));
    if ((features & (( << FEATURE_LEFT_ICON) | ( << FEATURE_RIGHT_ICON))) != ) {
        if (mIsFloating) {
            layoutResource = com.android.internal.R.layout.dialog_title_icons;
        } else {
            layoutResource = com.android.internal.R.layout.screen_title_icons;
        }
        // System.out.println("Title Icons!");
    } else if ((features & (( << FEATURE_PROGRESS) | ( << FEATURE_INDETERMINATE_PROGRESS))) != ) {
        // Special case for a window with only a progress bar (and title).
        // XXX Need to have a no-title version of embedded windows.
        layoutResource = com.android.internal.R.layout.screen_progress;
        // System.out.println("Progress!");
    } else if ((features & ( << FEATURE_CUSTOM_TITLE)) != ) {
        // Special case for a window with a custom title.
        // If the window is floating, we need a dialog layout
        if (mIsFloating) {
            layoutResource = com.android.internal.R.layout.dialog_custom_title;
        } else {
            layoutResource = com.android.internal.R.layout.screen_custom_title;
        }
    } else if ((features & ( << FEATURE_NO_TITLE)) == ) {
        // If no other features and not embedded, only need a title.
        // If the window is floating, we need a dialog layout
        if (mIsFloating) {
            layoutResource = com.android.internal.R.layout.dialog_title;
        } else {
            layoutResource = com.android.internal.R.layout.screen_title;
        }
        // System.out.println("Title!");
    } else {
        // Embedded, so no decoration is needed.
        layoutResource = com.android.internal.R.layout.screen_simple;
        // System.out.println("Simple!");
    }  

    mDecor.startChanging();
    // 3、加载视图
    View in = mLayoutInflater.inflate(layoutResource, null);
    // 4、将layoutResource的内容添加到mDecor中
    decor.addView(in, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));
    // 5、获取到我们的内容显示区域，这是一个ViewGroup类型的，其实是FrameLayout
    ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);
    if (contentParent == null) {
        throw new RuntimeException("Window couldn't find content container view");
    }  

    if ((features & ( << FEATURE_INDETERMINATE_PROGRESS)) != ) {
        ProgressBar progress = getCircularProgressBar(false);
        if (progress != null) {
            progress.setIndeterminate(true);
        }
    }  

    // 6、设置一些背景、title等属性
    // Remaining setup -- of background and title -- that only applies
    // to top-level windows.
    if (getContainer() == null) {
        Drawable drawable = mBackgroundDrawable;
        if (mBackgroundResource != ) {
            drawable = getContext().getResources().getDrawable(mBackgroundResource);
        }
        mDecor.setWindowBackground(drawable);
        drawable = null;
        if (mFrameResource != ) {
            drawable = getContext().getResources().getDrawable(mFrameResource);
        }
        mDecor.setWindowFrame(drawable);  

        // System.out.println("Text=" + Integer.toHexString(mTextColor) +
        // " Sel=" + Integer.toHexString(mTextSelectedColor) +
        // " Title=" + Integer.toHexString(mTitleColor));  

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

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

    mDecor.finishChanging();  

    return contentParent;  

其实也就是这么几个步骤：

1、获取用户设置的一些属性与Flag；

2、根据一些属性选择不同的顶层视图布局，例如FEATURE_NO_TITLE则选择没有title的布局文件等；这里我们看一个与图1中符合的顶层布局吧，即layoutResource = c

 <?xml version="1.0" encoding="utf-8"?>  

 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
     android:orientation="vertical"
     android:fitsSystemWindows="true">
     <!-- Popout bar for action modes -->
     <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" />
     <!--  title区域-->
     <FrameLayout
         android:layout_width="match_parent"
         android:layout_height="?android:attr/windowTitleSize"
         style="?android:attr/windowTitleBackgroundStyle">
         <TextView android:id="@android:id/title"
             style="?android:attr/windowTitleStyle"
             android:background="@null"
             android:fadingEdge="horizontal"
             android:gravity="center_vertical"
             android:layout_width="match_parent"
             android:layout_height="match_parent" />
     </FrameLayout>
     <!--内容显示区域, 例如main_activity.xml布局就会被放到这个ViewGroup下面 -->
     <FrameLayout android:id="@android:id/content"
         android:layout_width="match_parent"
         android:layout_height="0dip"
         android:layout_weight=""
         android:foregroundGravity="fill_horizontal|top"
         android:foreground="?android:attr/windowContentOverlay" />
 </LinearLayout>  

我们可以看到有两个区域，即title区域和content区域，generateLayout函数中的

// 5、获取到我们的内容显示区域，这是一个ViewGroup类型的，其实是FrameLayout
ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);  

获取的就是xml中id为content的FrameLayout，这个content就是我们的内容显示区域。整个布局对应的效果如下 :

这两个区域就组成了mDecor视图，我们的main_activity.xml就是放在内容视图这个区域的。

3、加载顶层布局文件，转换为View，将其添加到mDecor中；

4、获取内容容器Content Parent，即用于显示我们的内容的区域；

5、设置一些背景图和title等。

在经过这几步，我们就得到了mContentParent，这就是用来装载我们的视图的ViewGroup。再回过头来看setContentView函数：

 public void setContentView(int layoutResID) {
     if (mContentParent == null) {
         installDecor();         // 1、生成DecorView，并且根据窗口属性加载顶级视图布局、获取mContentParent、设置一些基本属性等
     } else {
         mContentParent.removeAllViews();
     }
     mLayoutInflater.inflate(layoutResID, mContentParent);// 2、将layoutResId加载到mContentParent中，这里的layoutResId就是我们的main_activity.xml
     final Callback cb = getCallback();
     if (cb != null) {
         cb.onContentChanged();
     }
 }  

我们看看LayoutInflater的inflate函数吧 :

 /**
  * Inflate a new view hierarchy from the specified xml resource. Throws
  * {@link InflateException} if there is an error.
  *
  * @param resource ID for an XML layout resource to load (e.g.,
  *        <code>R.layout.main_page</code>)
  * @param root Optional view to be the parent of the generated hierarchy.
  * @return The root View of the inflated hierarchy. If root was supplied,
  *         this is the root View; otherwise it is the root of the inflated
  *         XML file.
  */
 public View inflate(int resource, ViewGroup root) {
     return inflate(resource, root, root != null);
 }  

 /**
  * Inflate a new view hierarchy from the specified xml resource. Throws
  * {@link InflateException} if there is an error.
  *
  * @param resource ID for an XML layout resource to load (e.g.,
  *        <code>R.layout.main_page</code>)
  * @param root Optional view to be the parent of the generated hierarchy (if
  *        <em>attachToRoot</em> is true), or else simply an object that
  *        provides a set of LayoutParams values for root of the returned
  *        hierarchy (if <em>attachToRoot</em> is false.)
  * @param attachToRoot Whether the inflated hierarchy should be attached to
  *        the root parameter? If false, root is only used to create the
  *        correct subclass of LayoutParams for the root view in the XML.
  * @return The root View of the inflated hierarchy. If root was supplied and
  *         attachToRoot is true, this is root; otherwise it is the root of
  *         the inflated XML file.
  */
 public View inflate(int resource, ViewGroup root, boolean attachToRoot) {
     if (DEBUG) System.out.println("INFLATING from resource: " + resource);
     XmlResourceParser parser = getContext().getResources().getLayout(resource);
     try {
         return inflate(parser, root, attachToRoot);
     } finally {
         parser.close();
     }
 }  

实际上就是将layoutResId这个布局的视图附加到mContentParent中。

DecorView

移步 : DecorView 。

ViewGroup

ViewGroup从语义上来说就是视图组，它也继承自View类，它其实就是视图的容器。我们看官方的定义 :

* A ViewGroup is a special view that can contain other views
* (called children.) The view group is the base class for layouts and views
* containers. This class also defines the
* {@link android.view.ViewGroup.LayoutParams} class which serves as the base
* class for layouts parameters.  

我们通过ViewGroup来组织、管理子视图，例如我们常见的FrameLayout、LinearLayout、RelativeLayout、ListView等都是ViewGroup类型，总之只要能包含其他View或者ViewGroup的都是ViewGroup类型。使用ViewGroup来构建视图树。

View

View就是UI界面上的一个可见的组件，任何在UI上可见的都为View的子类。我们看官方定义 :

TextView、Button、ImageView、FrameLayout、LinearLayout、ListView等都是View的子类。

这样，ViewGroup类型的视图管理嵌套在里面的ViewGroup以及View控件组成了丰富多彩的用户界面。例如我们开篇的Hello World的视图结构是这样的 :

总结

整个窗口由Title区域和Content区域组成，Content区域就是我们要显示内容的区域，在这个区域中mContentParent是根ViewGroup，由mContentParent组织、管理其子视图，从而构建整个视图树。当Activity启动时，就将这些内容就会显示在手机上。