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Activity 中view 的布局

分类： Android平台

2013-12-20 18:47:36

       android 中view 代表一块图形区域。每一个view 都与一个依赖一个父view。在每一个Activity 中有一个Window  代表一个屏幕，包含一个View 树和窗口的layout 参数。View tree的root View可以通过getDecorView得到。 在 new 一个activity 时，通常把APK的view和布局通过setContentView(R.layout.activity_main)设置到View树中。  
      一.在activity中有一个：  private Window mWindow; 看一看这个mWindow是怎么来的：在Activity 的attach函数中：

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  1. mWindow = PolicyManager.makeNewWindow(this);
追踪一下这个函数，看一下调用流程：
./frameworks/base/core/java/com/android/internal/policy/PolicyManager.java：

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  1. package com.android.internal.policy;

  3. import android.content.Context;
  4. import android.view.FallbackEventHandler;
  5. import android.view.LayoutInflater;
  6. import android.view.Window;
  7. import android.view.WindowManagerPolicy;

  9. import com.android.internal.policy.IPolicy;

  11. /**
  12.  * {@hide}
  13.  */

  15. public final class PolicyManager {
  16.     private static final String POLICY_IMPL_CLASS_NAME =
  17.         "com.android.internal.policy.impl.Policy";

  19.     private static final IPolicy sPolicy;

  21.     static {
  22.         // Pull in the actual implementation of the policy at run-time
  23.         try {
  24.             Class policyClass = Class.forName(POLICY_IMPL_CLASS_NAME);
  25.             sPolicy = (IPolicy)policyClass.newInstance();
  26.         } catch (ClassNotFoundException ex) {
  27.             throw new RuntimeException(
  28.                     POLICY_IMPL_CLASS_NAME + " could not be loaded", ex);
  29.         } catch (InstantiationException ex) {
  30.             throw new RuntimeException(
  31.                     POLICY_IMPL_CLASS_NAME + " could not be instantiated", ex);
  32.         } catch (IllegalAccessException ex) {
  33.             throw new RuntimeException(
  34.                     POLICY_IMPL_CLASS_NAME + " could not be instantiated", ex);
  35.         }
  36.     }

  38.     // Cannot instantiate this class
  39.     private PolicyManager() {}

  41.     // The static methods to spawn new policy-specific objects
  42.     public static Window makeNewWindow(Context context) {
  43.         return sPolicy.makeNewWindow(context);
  44.     }

  46.     public static LayoutInflater makeNewLayoutInflater(Context context) {
  47.         return sPolicy.makeNewLayoutInflater(context);
  48.     }

  50.     public static WindowManagerPolicy makeNewWindowManager() {
  51.         return sPolicy.makeNewWindowManager();
  52.     }

  54.     public static FallbackEventHandler makeNewFallbackEventHandler(Context context) {
  55.         return sPolicy.makeNewFallbackEventHandler(context);
  56.     }
  57. }
这是一个 final 类，通过反射的方法获取一个com.android.internal.policy.impl.Policy类的静态对象：sPolicy，调用这个类的makeNewWindow：
./frameworks/base/policy/src/com/android/internal/policy/impl/Policy.java

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  1. package com.android.internal.policy.impl;

  3. import android.content.Context;
  4. import android.util.Log;
  5. import android.view.FallbackEventHandler;
  6. import android.view.LayoutInflater;
  7. import android.view.Window;
  8. import android.view.WindowManagerPolicy;

  10. import com.android.internal.policy.IPolicy;
  11. import com.android.internal.policy.impl.PhoneLayoutInflater;
  12. import com.android.internal.policy.impl.PhoneWindow;
  13. import com.android.internal.policy.impl.PhoneWindowManager;

  15. /**
  16.  * {@hide}
  17.  */

  19. // Simple implementation of the policy interface that spawns the right
  20. // set of objects
  21. public class Policy implements IPolicy {
  22.     private static final String TAG = "PhonePolicy";

  24.     private static final String[] preload_classes = {
  25.         "com.android.internal.policy.impl.PhoneLayoutInflater",
  26.         "com.android.internal.policy.impl.PhoneWindow",
  27.         "com.android.internal.policy.impl.PhoneWindow$1",
  28.         "com.android.internal.policy.impl.PhoneWindow$DialogMenuCallback",
  29.         "com.android.internal.policy.impl.PhoneWindow$DecorView",
  30.         "com.android.internal.policy.impl.PhoneWindow$PanelFeatureState",
  31.         "com.android.internal.policy.impl.PhoneWindow$PanelFeatureState$SavedState",
  32.     };

  34.     static {
  35.         // For performance reasons, preload some policy specific classes when
  36.         // the policy gets loaded.
  37.         for (String s : preload_classes) {
  38.             try {
  39.                 Class.forName(s);
  40.             } catch (ClassNotFoundException ex) {
  41.                 Log.e(TAG, "Could not preload class for phone policy: " + s);
  42.             }
  43.         }
  44.     }

  46.     public Window makeNewWindow(Context context) {
  47.         return new PhoneWindow(context);
  48.     }

  50.     public LayoutInflater makeNewLayoutInflater(Context context) {
  51.         return new PhoneLayoutInflater(context);
  52.     }

  54.     public WindowManagerPolicy makeNewWindowManager() {
  55.         return new PhoneWindowManager();
  56.     }

  58.     public FallbackEventHandler makeNewFallbackEventHandler(Context context) {
  59.         return new PhoneFallbackEventHandler(context);
  60.     }
  61. }
在这个类中返回了new PhoneWindow(context); 
./frameworks/base/policy/src/com/android/internal/policy/impl/PhoneWindow.java  现在我们找到了这个Window 对象。Window 的庐山真面目：

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  1. public class PhoneWindow extends Window implements MenuBuilder.Callback {
继承自 Window。window 的关系搞清楚了。
      二.在Activity中通过mWindow.getDecorView() 获取activity view树的布局。又来到了window 中。

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  1. public final View getDecorView() {
  2.         if (mDecor == null) {
  3.             installDecor();
  4.         }
  5.         return mDecor;
  6.     }
DecorView 是PhoneWindow的一个内部类：

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  1. private final class DecorView extends FrameLayout implements RootViewSurfaceTaker {
其实就是一个FrameLayout 布局，FrameLayout extend  ViewGroup。所有Activity 中的view 都添加到这个布局中。installDecor 函数：

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  1. private void installDecor() {
  2.         if (mDecor == null) {
  3.             mDecor = generateDecor();
  4.             mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);
  5.             mDecor.setIsRootNamespace(true);
  6.             if (!mInvalidatePanelMenuPosted && mInvalidatePanelMenuFeatures != 0) {
  7.                 mDecor.postOnAnimation(mInvalidatePanelMenuRunnable);
  8.             }
  9.         }
  10.         if (mContentParent == null) {
  11.             mContentParent = generateLayout(mDecor);
  12. ......
  13. }
    

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  1. protected DecorView generateDecor() {
  2.         return new DecorView(getContext(), -1);
  3.     }
      
这就是在PhoneWindow 的mDecorView 。需要注意一下mContentParent 这个变量。下面会分析到。
总结一下在一个Activity 中，有一个PhoneWindwo 对象，这个对象有有一个内部类Decorview ，Decorview extend  FrameLayout extend  ViewGroup 。这个Activity 的 view 都保存在这里，形成一个View 树。

      三.
Activity 的 setContentView:

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  1. public void setContentView(int layoutResID) {
  2.         getWindow().setContentView(layoutResID);
  3.         initActionBar();
  4.     }
PhoneWindow 的setContentView:

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  1. public void setContentView(int layoutResID) {
  2.         if (mContentParent == null) {
  3.             installDecor();
  4.         } else {
  5.             mContentParent.removeAllViews();
  6.         }
  7.         mLayoutInflater.inflate(layoutResID, mContentParent);
  8.         final Callback cb = getCallback();
  9.         if (cb != null && !isDestroyed()) {
  10.             cb.onContentChanged();
  11.         }
  12.     }
 mLayoutInflater.inflate(layoutResID, mContentParent); 在这行代码中，view 被设置进了mContentParent 这个父View中，在 PhoneWindow 中：
private ViewGroup  mContentParent

在刚才分析DecorView的时候， 在installDecor中会调用  mContentParent = generateLayout(mDecor)， 生成mContentParent；看一下实现：

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  1. protected ViewGroup generateLayout(DecorView decor) {
  2.         // Apply data from current theme.
  3.         ......

  5.         // Inflate the window decor.

  7.         int layoutResource;
  8.         int features = getLocalFeatures();
  9.         System.out.println("Features: 0x" + Integer.toHexString(features));
  10.         if ((features & ((1 << FEATURE_LEFT_ICON) | (1 << FEATURE_RIGHT_ICON))) != 0) {
  11.             if (mIsFloating) {
  12.                 TypedValue res = new TypedValue();
  13.                 getContext().getTheme().resolveAttribute(
  14.                         com.android.internal.R.attr.dialogTitleIconsDecorLayout, res, true);
  15.                 layoutResource = res.resourceId;
  16.             } else {
  17.                 layoutResource = com.android.internal.R.layout.screen_title_icons;
  18.                 System.out.println("layout.screen.title.icons");
  19.             }
  20.             // XXX Remove this once action bar supports these features.
  21.             removeFeature(FEATURE_ACTION_BAR);
  22.             // System.out.println("Title Icons!");
  23.         } else if ((features & ((1 << FEATURE_PROGRESS) | (1 << FEATURE_INDETERMINATE_PROGRESS))) != 0
  24.                 && (features & (1 << FEATURE_ACTION_BAR)) == 0) {
  25.             // Special case for a window with only a progress bar (and title).
  26.             // XXX Need to have a no-title version of embedded windows.
  27.             layoutResource = com.android.internal.R.layout.screen_progress;
  28.             // System.out.println("Progress!");
  29.         } else if ((features & (1 << FEATURE_CUSTOM_TITLE)) != 0) {
  30.             // Special case for a window with a custom title.
  31.             // If the window is floating, we need a dialog layout
  32.             if (mIsFloating) {
  33.                 TypedValue res = new TypedValue();
  34.                 getContext().getTheme().resolveAttribute(
  35.                         com.android.internal.R.attr.dialogCustomTitleDecorLayout, res, true);
  36.                 layoutResource = res.resourceId;
  37.             } else {
  38.                 layoutResource = com.android.internal.R.layout.screen_custom_title;
  39.             }
  40.             // XXX Remove this once action bar supports these features.
  41.             removeFeature(FEATURE_ACTION_BAR);
  42.         } else if ((features & (1 << FEATURE_NO_TITLE)) == 0) {
  43.             // If no other features and not embedded, only need a title.
  44.             // If the window is floating, we need a dialog layout
  45.             if (mIsFloating) {
  46.                 TypedValue res = new TypedValue();
  47.                 getContext().getTheme().resolveAttribute(
  48.                         com.android.internal.R.attr.dialogTitleDecorLayout, res, true);
  49.                 layoutResource = res.resourceId;
  50.             } else if ((features & (1 << FEATURE_ACTION_BAR)) != 0) {
  51.                 layoutResource = com.android.internal.R.layout.screen_action_bar;
  52.             } else {
  53.                 layoutResource = com.android.internal.R.layout.screen_title;
  54.             }
  55.             // System.out.println("Title!");
  56.         } else if ((features & (1 << FEATURE_ACTION_MODE_OVERLAY)) != 0) {
  57.             layoutResource = com.android.internal.R.layout.screen_simple_overlay_action_mode;
  58.         } else {
  59.             // Embedded, so no decoration is needed.
  60.             layoutResource = com.android.internal.R.layout.screen_simple;
  61.             // System.out.println("Simple!");
  62.         }

  64.         mDecor.startChanging();

  66.         View in = mLayoutInflater.inflate(layoutResource, null);
  67.         decor.addView(in, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));

  69.         ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);
  70.         if (contentParent == null) {
  71.             throw new RuntimeException("Window couldn't find content container view");
  72.         }

  74.         if ((features & (1 << FEATURE_INDETERMINATE_PROGRESS)) != 0) {
  75.             ProgressBar progress = getCircularProgressBar(false);
  76.             if (progress != null) {
  77.                 progress.setIndeterminate(true);
  78.             }
  79.         }

  81.         // Remaining setup -- of background and title -- that only applies
  82.         // to top-level windows.
  83.         if (getContainer() == null) {
  84.             Drawable drawable = mBackgroundDrawable;
  85.             if (mBackgroundResource != 0) {
  86.                 drawable = getContext().getResources().getDrawable(mBackgroundResource);
  87.             }
  88.             mDecor.setWindowBackground(drawable);
  89.             drawable = null;
  90.             if (mFrameResource != 0) {
  91.                 drawable = getContext().getResources().getDrawable(mFrameResource);
  92.             }
  93.             mDecor.setWindowFrame(drawable);

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

  99.             if (mTitleColor == 0) {
  100.                 mTitleColor = mTextColor;
  101.             }

  103.             if (mTitle != null) {
  104.                 setTitle(mTitle);
  105.             }
  106.             setTitleColor(mTitleColor);
  107.         }

  109.         mDecor.finishChanging();

  111.         return contentParent;
  112.     }
一开始获取一些窗口的属性，然后根据这些属性确定 layoutResource 的值，layoutResource 为com.android.internal.R.layout.screen_开头;就是 framework-res.apk里面的资源：src/android$ ls frameworks/base/core/res/res/layout/screen*
frameworks/base/core/res/res/layout/screen_action_bar.xml                  frameworks/base/core/res/res/layout/screen_simple.xml
frameworks/base/core/res/res/layout/screen_custom_title.xml                frameworks/base/core/res/res/layout/screen_title_icons.xml
frameworks/base/core/res/res/layout/screen_progress.xml                    frameworks/base/core/res/res/layout/screen_title.xml
frameworks/base/core/res/res/layout/screen_simple_overlay_action_mode.xml  frameworks/base/core/res/res/layout/screen.xml

然后解析：
  1. View in = mLayoutInflater.inflate(layoutResource, null);
  2.         decor.addView(in, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));

  4.         ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);
  5.         if (contentParent == null) {
  6.             throw new RuntimeException("Window couldn't find content container view");
  7.         }
contentParent 就是这些xml 文件里的一个ID_ANDROID_CONTENT 的view 。查找 ID_ANDROID_CONTENT定义：
frameworks/base/core/java/android/view/Window.java 124行：    
public static final int ID_ANDROID_CONTENT = com.android.internal.R.id.content;
打开 screen.xml 文件：

  1. <LinearLayout xmlns:android=""
  2.     android:layout_width="match_parent"
  3.     android:layout_height="match_parent"
  4.     android:fitsSystemWindows="true"
  5.     android:orientation="vertical">
  6.     <ViewStub android:id="@+id/action_mode_bar_stub"
  7.               android:inflatedId="@+id/action_mode_bar"
  8.               android:layout="@layout/action_mode_bar"
  9.               android:layout_width="match_parent"
  10.               android:layout_height="wrap_content" />
  11.     <FrameLayout
  12.          android:id="@android:id/content"
  13.          android:layout_width="match_parent"
  14.          android:layout_height="match_parent"
  15.          android:foregroundInsidePadding="false"
  16.          android:foregroundGravity="fill_horizontal|top"
  17.          android:foreground="?android:attr/windowContentOverlay" />
  18. </LinearLayout>
content 是一个FrameLayout的布局，在这几个screen_*.xml文件中 都有一个id为：content的View。也就是说 mDecorView 是一个Activity的根布局，contentParent是mDecorView 一个子布局，提供给程序员的View的根布局。setContentView 的时候以contentParent为父节点。

四.
 Activity的默认布局确定了，可以确定一下，修改xml 布局：

  1. diff --git a/base/core/res/res/layout/screen_simple.xml b/base/core/res/res/layout/screen_simple.xml
  2. index c1914e7..0b7f6e2 100644
  3. --- a/base/core/res/res/layout/screen_simple.xml
  4. +++ b/base/core/res/res/layout/screen_simple.xml
  5. @@ -25,7 +25,8 @@ enabled.
  6.      android:layout_width="match_parent"
  7.      android:layout_height="match_parent"
  8.      android:fitsSystemWindows="true"
  9. - android:orientation="vertical">
  10. + android:orientation="vertical"
  11. + android:background="@android:color/holo_orange_dark">
  12.      <ViewStub android:id="@+id/action_mode_bar_stub"
  13.                android:inflatedId="@+id/action_mode_bar"
  14.                android:layout="@layout/action_mode_bar"
  15. @@ -37,5 +38,6 @@ enabled.
  16.           android:layout_height="match_parent"
  17.           android:foregroundInsidePadding="false"
  18.           android:foregroundGravity="fill_horizontal|top"
  19. - android:foreground="?android:attr/windowContentOverlay" />
  20. + android:foreground="?android:attr/windowContentOverlay"
  21. + android:background="@android:color/holo_green_dark"/>
  22.  </LinearLayout>
当我们进入桌面的时候，桌面效果如下：
homeshell.png
进入HelloWorld,没有任何变化。分析generateLayout的时候已经看到会根据窗口的属性选择不同的资源文件。桌面和一般的Activity使用了不同的资源配置。
修改screen_action_bar.xml

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  1. diff --git a/base/core/res/res/layout/screen_action_bar.xml b/base/core/res/res/layout/screen_action_bar.xml
  2. index f0b2313..62b34f6 100644
  3. --- a/base/core/res/res/layout/screen_action_bar.xml
  4. +++ b/base/core/res/res/layout/screen_action_bar.xml
  5. @@ -23,33 +23,39 @@ This is an optimized layout for a screen with the Action Bar enabled.
  6.      android:layout_height="match_parent"
  7.      android:orientation="vertical"
  8.      android:fitsSystemWindows="true"
  9. - android:splitMotionEvents="false">
  10. + android:splitMotionEvents="false"
  11. + android:background="@android:color/holo_red_dark">
  12.      <com.android.internal.widget.ActionBarContainer android:id="@+id/action_bar_container"
  13.          android:layout_width="match_parent"
  14.          android:layout_height="wrap_content"
  15. - style="?android:attr/actionBarStyle">
  16. + style="?android:attr/actionBarStyle"
  17. + android:background="@android:color/holo_green_dark">
  18.          <com.android.internal.widget.ActionBarView
  19.              android:id="@+id/action_bar"
  20.              android:layout_width="match_parent"
  21.              android:layout_height="wrap_content"
  22. - style="?android:attr/actionBarStyle" />
  23. + style="?android:attr/actionBarStyle"
  24. + android:background="@android:color/holo_green_light"/>
  25.          <com.android.internal.widget.ActionBarContextView
  26.              android:id="@+id/action_context_bar"
  27.              android:layout_width="match_parent"
  28.              android:layout_height="wrap_content"
  29.              android:visibility="gone"
  30. - style="?android:attr/actionModeStyle" />
  31. + style="?android:attr/actionModeStyle"
  32. + android:background="@android:color/white"/>
  33.      </com.android.internal.widget.ActionBarContainer>
  34.      <FrameLayout android:id="@android:id/content"
  35.          android:layout_width="match_parent"
  36.          android:layout_height="0dip"
  37.          android:layout_weight="1"
  38.          android:foregroundGravity="fill_horizontal|top"
  39. - android:foreground="?android:attr/windowContentOverlay" />
  40. + android:foreground="?android:attr/windowContentOverlay"
  41. + android:background="@android:color/holo_orange_light"/>
  42.      <com.android.internal.widget.ActionBarContainer android:id="@+id/split_action_bar"
  43.                    android:layout_width="match_parent"
  44.                    android:layout_height="wrap_content"
  45.                    style="?android:attr/actionBarSplitStyle"
  46.                    android:visibility="gone"
  47. - android:gravity="center"/>
  48. + android:gravity="center"
  49. + android:background="@android:color/holo_blue_light"/>
  50.  </LinearLayout>
HelloWorld 的效果：
 activity.png
从图中可以看到根布局是一个FrameLayout布局，就是mDecorView.DecorView extend  FrameLayout。 被选中的区域为FrameLayout，就是mcontentParent，mcontentParent中有一个RelativeLayout,是我们setContentView 的R.layout.activity_main 布局文件。
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