Activity和Window关联源码分析

在Activity中，存在一个Window对象，现针对这个存在的window对象和activity之间的关系，进行分析：

在Activity的attach()方法中，进行成员变量mWindow的创建和初始化。

final void attach(Context context, ActivityThread aThread,
            Instrumentation instr, IBinder token, int ident,
            Application application, Intent intent, ActivityInfo info,
            CharSequence title, Activity parent, String id,
            Object lastNonConfigurationInstance,
            HashMap lastNonConfigurationChildInstances,
            Configuration config) {
        ......
        mWindow = PolicyManager.makeNewWindow(this);
        mWindow.setCallback(this);
        if (info.softInputMode != WindowManager.LayoutParams.SOFT_INPUT_STATE_UNSPECIFIED) {
            mWindow.setSoftInputMode(info.softInputMode);
        }
        ......
        mWindow.setWindowManager(null, mToken, mComponent.flattenToString());
        ......
        mWindowManager = mWindow.getWindowManager();
        ......
    }

其中mWindow对象调用PolicyManager的静态方法makeNewWindow(this)

public final class PolicyManager {
    private static final String POLICY_IMPL_CLASS_NAME =
        "com.android.internal.policy.impl.Policy";
    private static final IPolicy sPolicy;
    static {
        // Pull in the actual implementation of the policy at run-time
        try {
            Class policyClass = Class.forName(POLICY_IMPL_CLASS_NAME);
            sPolicy = (IPolicy)policyClass.newInstance();
        } catch (ClassNotFoundException ex) {
            throw new RuntimeException(
                    POLICY_IMPL_CLASS_NAME + " could not be loaded", ex);
        } catch (InstantiationException ex) {
            throw new RuntimeException(
                    POLICY_IMPL_CLASS_NAME + " could not be instantiated", ex);
        } catch (IllegalAccessException ex) {
            throw new RuntimeException(
                    POLICY_IMPL_CLASS_NAME + " could not be instantiated", ex);
        }
    }
    ......
    // The static methods to spawn new policy-specific objects
    public static Window makeNewWindow(Context context) {
        return sPolicy.makeNewWindow(context);
    }
    ......
}

在程序运行的时候，会调用静态代码块，生成一个IPolicy实例，实际上是通过类名反射出来的一个Policy对象，而PolicyManager.makeNewWindow返回的就是Policy的makeNewWindow,即是一个PhoneWindow。

public class Policy implements IPolicy {  
    ......  
    public PhoneWindow makeNewWindow(Context context) {  
        return new PhoneWindow(context);  
    }  
    ......  
}  

而PhoneWindow的创建，就是一个利用构造方法进行构造和初始化的过程：

public class PhoneWindow extends Window implements MenuBuilder.Callback {
    ......
    public PhoneWindow(Context context) {
        super(context);
        mLayoutInflater = LayoutInflater.from(context);
    }
    ......
}

在初始化之后，获取LayoutInflater对象，放在成员变量mLayoutInflater中，方便后面的mDecorView里面添加布局和子View。
在activity的attach()方法中，获取了mWindow对象之后，调用mWindow.setCallback()设置window的回调事件，而回调接口为在抽象类Window的内部：CallBack

public abstract class Window {
    ......
    public interface Callback {
        public boolean dispatchKeyEvent(KeyEvent event);
        public boolean dispatchTouchEvent(MotionEvent event);
        public boolean dispatchTrackballEvent(MotionEvent event);
        public boolean dispatchPopulateAccessibilityEvent(AccessibilityEvent event);
        public View onCreatePanelView(int featureId);
        public boolean onCreatePanelMenu(int featureId, Menu menu);
        public boolean onPreparePanel(int featureId, View view, Menu menu);
        public boolean onMenuOpened(int featureId, Menu menu);
        public boolean onMenuItemSelected(int featureId, MenuItem item);
        public void onWindowAttributesChanged(WindowManager.LayoutParams attrs);
        public void onContentChanged();
        public void onWindowFocusChanged(boolean hasFocus);
        public void onAttachedToWindow();
        public void onDetachedFromWindow();
        public void onPanelClosed(int featureId, Menu menu);
        public boolean onSearchRequested();
    }
    ......
}

而Activity又实现了此接口，自此，当PhoneWindow接受到系统的一系列事件，可以通过回调方法，在activity中进行接受和处理。
接着往下看，设置回调方法之后是判断软键盘的输入法显示模式（mWindow.setSoftInputMode(info.softInputMode)），再之后是设置mWindow的windowManager，这个方法在Window类中

public void setWindowManager(WindowManager wm, IBinder appToken, String appName) {
        mAppToken = appToken;
        mAppName = appName;
        if (wm == null) {
            wm = WindowManagerImpl.getDefault();
        }
        mWindowManager = new LocalWindowManager(wm);
    }

因为外面传进来的WindowManager是null，会进if判断，调用windowManagerImpl的静态方法getDefault():

public class WindowManagerImpl implements WindowManager {
    ......
    public static WindowManagerImpl getDefault(){
        return mWindowManager;
    }
    ......
    private static WindowManagerImpl mWindowManager = new WindowManagerImpl();
}

将获取的windowManager对象，作为一个参数，传递至LocalWindowManager构造方法中，此时生成mWindowManager对象，LocalWindowManager对mDefaultDisplay进行了包裹，而这个mWindowManager可通过activity的getWindowManager()或者是getWindow().getWindowManager()获得。

     private class LocalWindowManager implements WindowManager {
        LocalWindowManager(WindowManager wm) {
            mWindowManager = wm;
            mDefaultDisplay = mContext.getResources().getDefaultDisplay(
                    mWindowManager.getDefaultDisplay());
        }
        ......
        public Display getDefaultDisplay() {
            return mDefaultDisplay;
        }
        private final WindowManager mWindowManager;
        private final Display mDefaultDisplay;
    }

至此，activity和window的关联源码告一段落，总结一下：

1、Activity内部的Window对象，实际是PhoneWindow的实例
2、Activity的Window实例化过程，是在attach()方法中进行的，分别进行window构建和初始化，包括设置回调(setCallBack)、设置软键盘输入模式(setSoftInputMode)、和设置窗口管理器(setWindowManager)
3、Activity的getWindowManager()方法返回的，实际上是一个LocalWindowManager。
4、对于Activity内部的视图view操作，发生在PhoneWindow内部，即Activity的方法调用，最终会调取PhoneWindow内部方法，包括findViewById,setContentView等等