Android技术精髓-理解Context [源码]

Android技术精髓-理解Context [源码]

Context：

Context类是一个抽象类，定义应用程序环境的全局信息，它允许访问应用程序特定的资源和类，以及最新的电话应用程序级别的操作，例如： launching activities, broadcasting and receiving intents 等操作！

图1：Context定义的抽象方法以及全局变量

举个例子：

Context抽象类定义了StartActivity的方法，而并非是我们所想的在Activity中定义。

abstract void	startActivities(Intent[] intents, Bundle options) Launch multiple new activities.
abstract void	startActivities(Intent[] intents) Same as startActivities(Intent[], Bundle) with no options specified.
abstract void	startActivity(Intent intent) Same as startActivity(Intent, Bundle) with no options specified.
abstract void	startActivity(Intent intent, Bundle options) Launch a new activity.

在Android源代码中此抽象方法定义如下：

  public abstract void startActivity(Intent intent);

  public abstract boolean stopService(Intent service);

    
  public abstract boolean bindService(Intent service, ServiceConnection conn,
            int flags);

  public abstract void unbindService(ServiceConnection conn);

总结下：

1、它描述的是一个应用程序环境的信息，即上下文。

2、该类是一个抽象(abstract class)类，Android提供了该抽象类的具体实现类(后面我们会讲到是ContextIml类)。

3、通过它我们可以获取应用程序的资源和类，也包括一些应用级别操作，例如：启动一个Activity，发送广播，接受Intent信息 等。

Context相关类的继承关系

、

ContextIml.java类：

该Context类的实现类为ContextIml，该类实现了Context类的功能。请注意，该函数的大部分功能都是直接调用其属性mPackageInfo去完成

源码：

/**
 * Common implementation of Context API, which provides the base
 * context object for Activity and other application components.
 */
class ContextImpl extends Context {
    private final static String TAG = "ApplicationContext";
    private final static boolean DEBUG = false;
    private final static boolean DEBUG_ICONS = false;

//以下选择部分function实现源码贴出

 @Override
    public PackageManager getPackageManager() {
        if (mPackageManager != null) {
            return mPackageManager;
        }


        IPackageManager pm = ActivityThread.getPackageManager();
        if (pm != null) {
            // Doesn't matter if we make more than one instance.
            return (mPackageManager = new ApplicationPackageManager(this, pm));
        }


        return null;
    }

  @Override
    public void setTheme(int resid) {
        mThemeResource = resid;
    }
    
    @Override
    public Resources.Theme getTheme() {
        if (mTheme == null) {
            if (mThemeResource == 0) {
                mThemeResource = com.android.internal.R.style.Theme;
            }
            mTheme = mResources.newTheme();
            mTheme.applyStyle(mThemeResource, true);
        }
        return mTheme;
    }

  private static File makeBackupFile(File prefsFile) {
        return new File(prefsFile.getPath() + ".bak");
    }


    public File getSharedPrefsFile(String name) {
        return makeFilename(getPreferencesDir(), name + ".xml");
    }


    @Override
    public SharedPreferences getSharedPreferences(String name, int mode) {
        SharedPreferencesImpl sp;
        File prefsFile;
        boolean needInitialLoad = false;
        synchronized (sSharedPrefs) {
            sp = sSharedPrefs.get(name);
            if (sp != null && !sp.hasFileChangedUnexpectedly()) {
                return sp;
            }
            prefsFile = getSharedPrefsFile(name);
            if (sp == null) {
                sp = new SharedPreferencesImpl(prefsFile, mode, null);
                sSharedPrefs.put(name, sp);
                needInitialLoad = true;
            }
        }


        synchronized (sp) {
            if (needInitialLoad && sp.isLoaded()) {
                // lost the race to load; another thread handled it
                return sp;
            }
            File backup = makeBackupFile(prefsFile);
            if (backup.exists()) {
                prefsFile.delete();
                backup.renameTo(prefsFile);
            }


            // Debugging
            if (prefsFile.exists() && !prefsFile.canRead()) {
                Log.w(TAG, "Attempt to read preferences file " + prefsFile + " without permission");
            }


            Map map = null;
            FileStatus stat = new FileStatus();
            if (FileUtils.getFileStatus(prefsFile.getPath(), stat) && prefsFile.canRead()) {
                try {
                    FileInputStream str = new FileInputStream(prefsFile);
                    map = XmlUtils.readMapXml(str);
                    str.close();
                } catch (org.xmlpull.v1.XmlPullParserException e) {
                    Log.w(TAG, "getSharedPreferences", e);
                } catch (FileNotFoundException e) {
                    Log.w(TAG, "getSharedPreferences", e);
                } catch (IOException e) {
                    Log.w(TAG, "getSharedPreferences", e);
                }
            }
            sp.replace(map, stat);
        }
        return sp;
    }


    private File getPreferencesDir() {
        synchronized (mSync) {
            if (mPreferencesDir == null) {
                mPreferencesDir = new File(getDataDirFile(), "shared_prefs");
            }
            return mPreferencesDir;
        }
    }


    @Override
    public FileInputStream openFileInput(String name)
        throws FileNotFoundException {
        File f = makeFilename(getFilesDir(), name);
        return new FileInputStream(f);
    }


    @Override
    public FileOutputStream openFileOutput(String name, int mode)
        throws FileNotFoundException {
        final boolean append = (mode&MODE_APPEND) != 0;
        File f = makeFilename(getFilesDir(), name);
        try {
            FileOutputStream fos = new FileOutputStream(f, append);
            setFilePermissionsFromMode(f.getPath(), mode, 0);
            return fos;
        } catch (FileNotFoundException e) {
        }


        File parent = f.getParentFile();
        parent.mkdir();
        FileUtils.setPermissions(
            parent.getPath(),
            FileUtils.S_IRWXU|FileUtils.S_IRWXG|FileUtils.S_IXOTH,
            -1, -1);
        FileOutputStream fos = new FileOutputStream(f, append);
        setFilePermissionsFromMode(f.getPath(), mode, 0);
        return fos;
    }


    @Override
    public boolean deleteFile(String name) {
        File f = makeFilename(getFilesDir(), name);
        return f.delete();
    }

  @Override
    public File getFilesDir() {
        synchronized (mSync) {
            if (mFilesDir == null) {
                mFilesDir = new File(getDataDirFile(), "files");
            }
            if (!mFilesDir.exists()) {
                if(!mFilesDir.mkdirs()) {
                    Log.w(TAG, "Unable to create files directory");
                    return null;
                }
                FileUtils.setPermissions(
                        mFilesDir.getPath(),
                        FileUtils.S_IRWXU|FileUtils.S_IRWXG|FileUtils.S_IXOTH,
                        -1, -1);
            }
            return mFilesDir;
        }
    }

 @Override
    public void startActivity(Intent intent) {
        if ((intent.getFlags()&Intent.FLAG_ACTIVITY_NEW_TASK) == 0) {
            throw new AndroidRuntimeException(
                    "Calling startActivity() from outside of an Activity "
                    + " context requires the FLAG_ACTIVITY_NEW_TASK flag."
                    + " Is this really what you want?");
        }
        mMainThread.getInstrumentation().execStartActivity(
            getOuterContext(), mMainThread.getApplicationThread(), null, null, intent, -1);
    }

    @Override
    public void sendBroadcast(Intent intent, String receiverPermission) {
        String resolvedType = intent.resolveTypeIfNeeded(getContentResolver());
        try {
            ActivityManagerNative.getDefault().broadcastIntent(
                mMainThread.getApplicationThread(), intent, resolvedType, null,
                Activity.RESULT_OK, null, null, receiverPermission, false, false);
        } catch (RemoteException e) {
        }
    }

   @Override
    public ComponentName startService(Intent service) {
        try {
            ComponentName cn = ActivityManagerNative.getDefault().startService(
                mMainThread.getApplicationThread(), service,
                service.resolveTypeIfNeeded(getContentResolver()));
            if (cn != null && cn.getPackageName().equals("!")) {
                throw new SecurityException(
                        "Not allowed to start service " + service
                        + " without permission " + cn.getClassName());
            }
            return cn;
        } catch (RemoteException e) {
            return null;
        }
    }


    @Override
    public boolean stopService(Intent service) {
        try {
            int res = ActivityManagerNative.getDefault().stopService(
                mMainThread.getApplicationThread(), service,
                service.resolveTypeIfNeeded(getContentResolver()));
            if (res < 0) {
                throw new SecurityException(
                        "Not allowed to stop service " + service);
            }
            return res != 0;
        } catch (RemoteException e) {
            return false;
        }
    }


    @Override
    public boolean bindService(Intent service, ServiceConnection conn,
            int flags) {
        IServiceConnection sd;
        if (mPackageInfo != null) {
            sd = mPackageInfo.getServiceDispatcher(conn, getOuterContext(),
                    mMainThread.getHandler(), flags);
        } else {
            throw new RuntimeException("Not supported in system context");
        }
        try {
            int res = ActivityManagerNative.getDefault().bindService(
                mMainThread.getApplicationThread(), getActivityToken(),
                service, service.resolveTypeIfNeeded(getContentResolver()),
                sd, flags);
            if (res < 0) {
                throw new SecurityException(
                        "Not allowed to bind to service " + service);
            }
            return res != 0;
        } catch (RemoteException e) {
            return false;
        }
    }


    @Override
    public void unbindService(ServiceConnection conn) {
        if (mPackageInfo != null) {
            IServiceConnection sd = mPackageInfo.forgetServiceDispatcher(
                    getOuterContext(), conn);
            try {
                ActivityManagerNative.getDefault().unbindService(sd);
            } catch (RemoteException e) {
            }
        } else {
            throw new RuntimeException("Not supported in system context");
        }
    }


    @Override
    public Object getSystemService(String name) {
        if (WINDOW_SERVICE.equals(name)) {
            return WindowManagerImpl.getDefault();
        } else if (LAYOUT_INFLATER_SERVICE.equals(name)) {
            synchronized (mSync) {
                LayoutInflater inflater = mLayoutInflater;
                if (inflater != null) {
                    return inflater;
                }
                mLayoutInflater = inflater =
                    PolicyManager.makeNewLayoutInflater(getOuterContext());
                return inflater;
            }
        } else if (ACTIVITY_SERVICE.equals(name)) {
            return getActivityManager();
        } else if (INPUT_METHOD_SERVICE.equals(name)) {
            return InputMethodManager.getInstance(this);
        } else if (ALARM_SERVICE.equals(name)) {
            return getAlarmManager();
        } else if (ACCOUNT_SERVICE.equals(name)) {
            return getAccountManager();
        } else if (POWER_SERVICE.equals(name)) {
            return getPowerManager();
        } else if (CONNECTIVITY_SERVICE.equals(name)) {
            return getConnectivityManager();
        } else if (THROTTLE_SERVICE.equals(name)) {
            return getThrottleManager();
        } else if (WIFI_SERVICE.equals(name)) {
            return getWifiManager();
        } else if (NOTIFICATION_SERVICE.equals(name)) {
            return getNotificationManager();
        } else if (KEYGUARD_SERVICE.equals(name)) {
            return new KeyguardManager();
        } else if (ACCESSIBILITY_SERVICE.equals(name)) {
            return AccessibilityManager.getInstance(this);
        } else if (LOCATION_SERVICE.equals(name)) {
            return getLocationManager();
        } else if (SEARCH_SERVICE.equals(name)) {
            return getSearchManager();
        } else if (SENSOR_SERVICE.equals(name)) {
            return getSensorManager();
        } else if (STORAGE_SERVICE.equals(name)) {
            return getStorageManager();
        } else if (VIBRATOR_SERVICE.equals(name)) {
            return getVibrator();
        } else if (STATUS_BAR_SERVICE.equals(name)) {
            synchronized (mSync) {
                if (mStatusBarManager == null) {
                    mStatusBarManager = new StatusBarManager(getOuterContext());
                }
                return mStatusBarManager;
            }
        } else if (AUDIO_SERVICE.equals(name)) {
            return getAudioManager();
        } else if (TELEPHONY_SERVICE.equals(name)) {
            return getTelephonyManager();
        } else if (CLIPBOARD_SERVICE.equals(name)) {
            return getClipboardManager();
        } else if (WALLPAPER_SERVICE.equals(name)) {
            return getWallpaperManager();
        } else if (DROPBOX_SERVICE.equals(name)) {
            return getDropBoxManager();
        } else if (DEVICE_POLICY_SERVICE.equals(name)) {
            return getDevicePolicyManager();
        } else if (UI_MODE_SERVICE.equals(name)) {
            return getUiModeManager();
        } else if (DOWNLOAD_SERVICE.equals(name)) {
            return getDownloadManager();
        } else if (NFC_SERVICE.equals(name)) {
            return getNfcManager();
        }


        return null;
    }

ContextWrapper类 ：

该类只是对Context类的一种包装，该类的构造函数包含了一个真正的Context引用，即ContextIml对象

源码：

public class ContextWrapper extends Context {
    Context mBase;

    public ContextWrapper(Context base) {
        mBase = base;
    }
    
    /**
     * Set the base context for this ContextWrapper.  All calls will then be
     * delegated to the base context.  Throws
     * IllegalStateException if a base context has already been set.
     * 
     * @param base The new base context for this wrapper.
     */
    protected void attachBaseContext(Context base) {
        if (mBase != null) {
            throw new IllegalStateException("Base context already set");
        }
        mBase = base;
    }

    /**
     * @return the base context as set by the constructor or setBaseContext
     */
    public Context getBaseContext() {
        return mBase;
    }

    @Override
    public AssetManager getAssets() {
        return mBase.getAssets();
    }

    @Override
    public Resources getResources()
    {
        return mBase.getResources();
    }

    @Override
    public PackageManager getPackageManager() {
        return mBase.getPackageManager();
    }

    @Override
    public ContentResolver getContentResolver() {
        return mBase.getContentResolver();
    }

    @Override
    public Looper getMainLooper() {
        return mBase.getMainLooper();
    }
    
    @Override
    public Context getApplicationContext() {
        return mBase.getApplicationContext();
    }
    
    @Override
    public void setTheme(int resid) {
        mBase.setTheme(resid);
    }

    @Override
    public Resources.Theme getTheme() {
        return mBase.getTheme();
    }

    @Override
    public ClassLoader getClassLoader() {
        return mBase.getClassLoader();
    }

    @Override
    public String getPackageName() {
        return mBase.getPackageName();
    }

    @Override
    public ApplicationInfo getApplicationInfo() {
        return mBase.getApplicationInfo();
    }
    
    @Override
    public String getPackageResourcePath() {
        return mBase.getPackageResourcePath();
    }

    @Override
    public String getPackageCodePath() {
        return mBase.getPackageCodePath();
    }

    /** @hide */
    @Override
    public File getSharedPrefsFile(String name) {
        return mBase.getSharedPrefsFile(name);
    }

    @Override
    public SharedPreferences getSharedPreferences(String name, int mode) {
        return mBase.getSharedPreferences(name, mode);
    }

    @Override
    public FileInputStream openFileInput(String name)
        throws FileNotFoundException {
        return mBase.openFileInput(name);
    }

    @Override
    public FileOutputStream openFileOutput(String name, int mode)
        throws FileNotFoundException {
        return mBase.openFileOutput(name, mode);
    }

    @Override
    public boolean deleteFile(String name) {
        return mBase.deleteFile(name);

ContextThemeWrapper类 ：

该类内部包含了主题(Theme)相关的接口，即android:theme属性指定的。只有Activity需要主题，Service不需要主题， 所以Service直接继承于ContextWrapper类。

源码：

/**
 * A ContextWrapper that allows you to modify the theme from what is in the 
 * wrapped context. 
 */
public class ContextThemeWrapper extends ContextWrapper {
    private Context mBase;
    private int mThemeResource;
    private Resources.Theme mTheme;
    private LayoutInflater mInflater;

    public ContextThemeWrapper() {
        super(null);
    }
    
    public ContextThemeWrapper(Context base, int themeres) {
        super(base);
        mBase = base;
        mThemeResource = themeres;
    }

    @Override protected void attachBaseContext(Context newBase) {
        super.attachBaseContext(newBase);
        mBase = newBase;
    }
    
    @Override public void setTheme(int resid) {
        mThemeResource = resid;
        initializeTheme();
    }
    
    @Override public Resources.Theme getTheme() {
        if (mTheme != null) {
            return mTheme;
        }

        if (mThemeResource == 0) {
            mThemeResource = com.android.internal.R.style.Theme;
        }
        initializeTheme();

        return mTheme;
    }

    @Override public Object getSystemService(String name) {
        if (LAYOUT_INFLATER_SERVICE.equals(name)) {
            if (mInflater == null) {
                mInflater = LayoutInflater.from(mBase).cloneInContext(this);
            }
            return mInflater;
        }
        return mBase.getSystemService(name);
    }
    
    /**
     * Called by {@link #setTheme} and {@link #getTheme} to apply a theme
     * resource to the current Theme object.  Can override to change the
     * default (simple) behavior.  This method will not be called in multiple
     * threads simultaneously.
     *
     * @param theme The Theme object being modified.
     * @param resid The theme style resource being applied to <var>theme</var>.
     * @param first Set to true if this is the first time a style is being
     *              applied to <var>theme</var>.
     */
    protected void onApplyThemeResource(Resources.Theme theme, int resid, boolean first) {
        theme.applyStyle(resid, true);
    }

    private void initializeTheme() {
        final boolean first = mTheme == null;
        if (first) {
            mTheme = getResources().newTheme();
            Resources.Theme theme = mBase.getTheme();
            if (theme != null) {
                mTheme.setTo(theme);
            }
        }
        onApplyThemeResource(mTheme, mThemeResource, first);
    }
}

Activity类 、Service类 、Application类本质上都是Context子类。

Activity类源码（部分）：

public class Activity extends ContextThemeWrapper
        implements LayoutInflater.Factory,
        Window.Callback, KeyEvent.Callback,
        OnCreateContextMenuListener, ComponentCallbacks {
    private static final String TAG = "Activity";

  public static long getInstanceCount() {
        return sInstanceCount;
    }


    /** Return the intent that started this activity. */
    public Intent getIntent() {
        return mIntent;
    }


    /** 
     * Change the intent returned by {@link #getIntent}.  This holds a 
     * reference to the given intent; it does not copy it.  Often used in 
     * conjunction with {@link #onNewIntent}. 
     *  
     * @param newIntent The new Intent object to return from getIntent 
     * 
     * @see #getIntent
     * @see #onNewIntent
     */ 
    public void setIntent(Intent newIntent) {
        mIntent = newIntent;
    }


    /** Return the application that owns this activity. */
    public final Application getApplication() {
        return mApplication;
    }


    /** Is this activity embedded inside of another activity? */
    public final boolean isChild() {
        return mParent != null;
    }
    
    /** Return the parent activity if this view is an embedded child. */
    public final Activity getParent() {
        return mParent;
    }


    /** Retrieve the window manager for showing custom windows. */
    public WindowManager getWindowManager() {
        return mWindowManager;
    }


      /**
     * Called when the activity is starting.  This is where most initialization
     * should go: calling {@link #setContentView(int)} to inflate the
     * activity's UI, using {@link #findViewById} to programmatically interact
     * with widgets in the UI, calling
     * {@link #managedQuery(android.net.Uri , String[], String, String[], String)} to retrieve
     * cursors for data being displayed, etc.
     * 
     * <p>You can call {@link #finish} from within this function, in
     * which case onDestroy() will be immediately called without any of the rest
     * of the activity lifecycle ({@link #onStart}, {@link #onResume},
     * {@link #onPause}, etc) executing.
     * 
     * <p><em>Derived classes must call through to the super class's
     * implementation of this method.  If they do not, an exception will be
     * thrown.</em></p>
     * 
     * @param savedInstanceState If the activity is being re-initialized after
     *     previously being shut down then this Bundle contains the data it most
     *     recently supplied in {@link #onSaveInstanceState}.  <b><i>Note: Otherwise it is null.</i></b>
     * 
     * @see #onStart
     * @see #onSaveInstanceState
     * @see #onRestoreInstanceState
     * @see #onPostCreate
     */
    protected void onCreate(Bundle savedInstanceState) {         mVisibleFromClient = !mWindow.getWindowStyle().getBoolean(                 com.android.internal.R.styleable.Window_windowNoDisplay, false);         mCalled = true;     }

private Dialog createDialog(Integer dialogId, Bundle state, Bundle args) {
        final Dialog dialog = onCreateDialog(dialogId, args);
        if (dialog == null) {
            return null;
        }
        dialog.dispatchOnCreate(state);
        return dialog;
    }

    protected void onDestroy() {
        mCalled = true;


        // dismiss any dialogs we are managing.
        if (mManagedDialogs != null) {
            final int numDialogs = mManagedDialogs.size();
            for (int i = 0; i < numDialogs; i++) {
                final ManagedDialog md = mManagedDialogs.valueAt(i);
                if (md.mDialog.isShowing()) {
                    md.mDialog.dismiss();
                }
            }
            mManagedDialogs = null;
        }


        // close any cursors we are managing.
        synchronized (mManagedCursors) {
            int numCursors = mManagedCursors.size();
            for (int i = 0; i < numCursors; i++) {
                ManagedCursor c = mManagedCursors.get(i);
                if (c != null) {
                    c.mCursor.close();
                }
            }
            mManagedCursors.clear();
        }


        // Close any open search dialog
        if (mSearchManager != null) {
            mSearchManager.stopSearch();
        }
    }

  /**
     * Called when a key was pressed down and not handled by any of the views
     * inside of the activity. So, for example, key presses while the cursor 
     * is inside a TextView will not trigger the event (unless it is a navigation
     * to another object) because TextView handles its own key presses.
     * 
     * <p>If the focused view didn't want this event, this method is called.
     *
     * <p>The default implementation takes care of {@link KeyEvent#KEYCODE_BACK}
     * by calling {@link #onBackPressed()}, though the behavior varies based
     * on the application compatibility mode: for
     * {@link android.os.Build.VERSION_CODES#ECLAIR} or later applications,
     * it will set up the dispatch to call {@link #onKeyUp} where the action
     * will be performed; for earlier applications, it will perform the
     * action immediately in on-down, as those versions of the platform
     * behaved.
     * 
     * <p>Other additional default key handling may be performed
     * if configured with {@link #setDefaultKeyMode}.
     * 
     * @return Return <code>true</code> to prevent this event from being propagated
     * further, or <code>false</code> to indicate that you have not handled 
     * this event and it should continue to be propagated.
     * @see #onKeyUp
     * @see android.view.KeyEvent
     */
    public boolean onKeyDown(int keyCode, KeyEvent event)  {
        if (keyCode == KeyEvent.KEYCODE_BACK) {
            if (getApplicationInfo().targetSdkVersion
                    >= Build.VERSION_CODES.ECLAIR) {
                event.startTracking();
            } else {
                onBackPressed();
            }
            return true;
        }
        
        if (mDefaultKeyMode == DEFAULT_KEYS_DISABLE) {
            return false;
        } else if (mDefaultKeyMode == DEFAULT_KEYS_SHORTCUT) {
            if (getWindow().performPanelShortcut(Window.FEATURE_OPTIONS_PANEL, 
                    keyCode, event, Menu.FLAG_ALWAYS_PERFORM_CLOSE)) {
                return true;
            }
            return false;
        } else {
            // Common code for DEFAULT_KEYS_DIALER & DEFAULT_KEYS_SEARCH_*
            boolean clearSpannable = false;
            boolean handled;
            if ((event.getRepeatCount() != 0) || event.isSystem()) {
                clearSpannable = true;
                handled = false;
            } else {
                handled = TextKeyListener.getInstance().onKeyDown(
                        null, mDefaultKeySsb, keyCode, event);
                if (handled && mDefaultKeySsb.length() > 0) {
                    // something useable has been typed - dispatch it now.


                    final String str = mDefaultKeySsb.toString();
                    clearSpannable = true;
                    
                    switch (mDefaultKeyMode) {
                    case DEFAULT_KEYS_DIALER:
                        Intent intent = new Intent(Intent.ACTION_DIAL,  Uri.parse("tel:" + str));
                        intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
                        startActivity(intent);    
                        break;
                    case DEFAULT_KEYS_SEARCH_LOCAL:
                        startSearch(str, false, null, false);
                        break;
                    case DEFAULT_KEYS_SEARCH_GLOBAL:
                        startSearch(str, false, null, true);
                        break;
                    }
                }
            }
            if (clearSpannable) {
                mDefaultKeySsb.clear();
                mDefaultKeySsb.clearSpans();
                Selection.setSelection(mDefaultKeySsb,0);
            }
            return handled;
        }
    }


    /**
     * Default implementation of {@link KeyEvent.Callback#onKeyLongPress(int, KeyEvent)
     * KeyEvent.Callback.onKeyLongPress()}: always returns false (doesn't handle
     * the event).
     */
    public boolean onKeyLongPress(int keyCode, KeyEvent event) {
        return false;
    }


    public boolean onKeyUp(int keyCode, KeyEvent event) {
        if (getApplicationInfo().targetSdkVersion
                >= Build.VERSION_CODES.ECLAIR) {
            if (keyCode == KeyEvent.KEYCODE_BACK && event.isTracking()
                    && !event.isCanceled()) {
                onBackPressed();
                return true;
            }
        }
        return false;
    }


    /**
     * Default implementation of {@link KeyEvent.Callback#onKeyMultiple(int, int, KeyEvent)
     * KeyEvent.Callback.onKeyMultiple()}: always returns false (doesn't handle
     * the event).
     */
    public boolean onKeyMultiple(int keyCode, int repeatCount, KeyEvent event) {
        return false;
    }
    
    /**
     * Called when the activity has detected the user's press of the back
     * key.  The default implementation simply finishes the current activity,
     * but you can override this to do whatever you want.
     */
    public void onBackPressed() {
        finish();
    }
    

  @Override
    public void startActivity(Intent intent) {
        startActivityForResult(intent, -1);
    }

    public void startActivityFromChild(Activity child, Intent intent, 
            int requestCode) {
        Instrumentation.ActivityResult ar =
            mInstrumentation.execStartActivity(
                this, mMainThread.getApplicationThread(), mToken, child,
                intent, requestCode);
        if (ar != null) {
            mMainThread.sendActivityResult(
                mToken, child.mEmbeddedID, requestCode,
                ar.getResultCode(), ar.getResultData());
        }
    }

   public void finish() {
        if (mParent == null) {
            int resultCode;
            Intent resultData;
            synchronized (this) {
                resultCode = mResultCode;
                resultData = mResultData;
            }
            if (Config.LOGV) Log.v(TAG, "Finishing self: token=" + mToken);
            try {
                if (ActivityManagerNative.getDefault()
                    .finishActivity(mToken, resultCode, resultData)) {
                    mFinished = true;
                }
            } catch (RemoteException e) {
                // Empty
            }
        } else {
            mParent.finishFromChild(this);
        }
    }

  public void finishFromChild(Activity child) {
        finish();
    }


    /**
     * Force finish another activity that you had previously started with
     * {@link #startActivityForResult}.
     * 
     * @param requestCode The request code of the activity that you had
     *                    given to startActivityForResult().  If there are multiple
     *                    activities started with this request code, they
     *                    will all be finished.
     */
    public void finishActivity(int requestCode) {
        if (mParent == null) {
            try {
                ActivityManagerNative.getDefault()
                    .finishSubActivity(mToken, mEmbeddedID, requestCode);
            } catch (RemoteException e) {
                // Empty
            }
        } else {
            mParent.finishActivityFromChild(this, requestCode);
        }
    }
 {