将 Activity 转换为 MainActivity 时出现 ClassCastException

Question

我的 Android 应用程序在将 Activity 投射到我的 MainActivity 时遇到了一个奇怪的问题。我正在使用 GeoFences 将事件广播到名为 NotificationActivity 的基础 activity。 NotificationActivity 用于我使用的所有其他活动，因此当 GeoFence 触发 AlertDialog 弹出时。现在，当 GeoFence 触发并且我处于 MainActivity 以外的 activity 时，我需要完成当前 activity 并在 MainActivity 上执行特定操作（切换到某个选项卡）。在我的应用程序 class 中，我正在实施 Application.ActivityLifeCycleCallbacks，在 onActivityResumed 回调中，我将 currentActivity 设置为已恢复 activity （我知道一个静态引用会导致内存泄漏，但我需要解决这个问题）。

这是我的申请 class:

private static Activity currentActivity;

@Override
public void onCreate() {
    super.onCreate();

    // Setup Fabric
    if (AppConfig.getEnvironment() != AppConfig.Environment.Development) {
        Fabric.with(this, new Crashlytics(), new Answers());
    }

    // Init realm
    Realm.init(this);

    // Init Firebase
    FirebaseApp.initializeApp(this);

    if (AppConfig.getEnvironment() == AppConfig.Environment.Development) {
        // Init Stetho with realm plugin
        Stetho.initialize (
                Stetho.newInitializerBuilder(this)
                        .enableDumpapp(Stetho.defaultDumperPluginsProvider(this))
                        .enableWebKitInspector(RealmInspectorModulesProvider.builder(this).build())
                        .build());
    }

    registerActivityLifecycleCallbacks(this);
}

@Override
public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
    Log.d(Constants.DEBUG, "Activity created: " + activity.toString());
}

@Override
public void onActivityStarted(Activity activity) {
    Log.d(Constants.DEBUG, "Activity started: " + activity.toString());
}

@Override
public void onActivityResumed(Activity activity) {
    Log.d(Constants.DEBUG, "Activity resumed: " + activity.toString());
    currentActivity = activity;
}

@Override
public void onActivityPaused(Activity activity) {
    Log.d(Constants.DEBUG, "Activity paused: " + activity.toString());
}

@Override
public void onActivityStopped(Activity activity) {
    Log.d(Constants.DEBUG, "Activity stopped: " + activity.toString());
}

@Override
public void onActivitySaveInstanceState(Activity activity, Bundle outState) {
    Log.d(Constants.DEBUG, "Activity SaveInstanceState: " + activity.toString());
}

@Override
public void onActivityDestroyed(Activity activity) {
    Log.d(Constants.DEBUG, "Activity Destroyed: " + activity.toString());
}

public static Activity getCurrentActivity() {
    return currentActivity;
}

这是我的通知Activity（基础）activity:

public abstract class NotificationActivity extends AppCompatActivity {

private BroadcastReceiver onNoticeWithinPoi = new BroadcastReceiver() {

    @Override
    public void onReceive(Context context, Intent intent) {
        abortBroadcast();
        Bundle bundle = intent.getExtras();
        if (bundle != null) {
            Realm realm = Realm.getDefaultInstance();
            Poi poi = realm.where(Poi.class).equalTo("ref", bundle.getString(Constants.POI_KEY_REF)).findFirst();
            showAlertWithinPoi(context, poi);
        }
    }
};

private BroadcastReceiver onNoLocationProviderSet = new BroadcastReceiver() {

    @Override
    public void onReceive(Context context, Intent intent) {
        warnUserNoLocationProviderSet();
    }
};

private BroadcastReceiver onNoticeOutOfRange = new BroadcastReceiver() {

    @Override
    public void onReceive(Context context, Intent intent) {
        abortBroadcast();
        alertNoticeOutOfRange();
    }
};

public Fragment getActiveFragment() {
    if (getFragmentManager().getBackStackEntryCount() == 0) {
        return null;
    }

    String tag = getFragmentManager().getBackStackEntryAt(getFragmentManager().getBackStackEntryCount() - 1).getName();
    return getFragmentManager().findFragmentByTag(tag);
}

private void showAlertWithinPoi(final Context context, final Poi poi) {
    AlertDialog.Builder builder =  new AlertDialog.Builder(this);
    builder.setTitle(getString(R.string.poi_popup_title));
    builder.setMessage(getString(R.string.poi_popup_subtitle));
    builder.setPositiveButton(getString(R.string.yes), new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialog, int which) {
            Game currentGame = Helper.getCurrentGame(context);
            Game poiGame = null;

            Realm realm = Realm.getDefaultInstance();
            for (Game game : realm.where(Game.class).findAll()) {
                for (Tag tag : game.tags) {
                    if (tag.poi.ref.equals(poi.ref)) {
                        poiGame = game;
                        break;
                    }
                }

                if (poiGame != null) {
                    break;
                }
            }

            if (poiGame != null && poiGame.ref.equals(currentGame.ref)) {
                realm.beginTransaction();
                currentGame.lastSeenPoi = poi.ref;
                realm.commitTransaction();
                checkCurrentActivity();
            } else if (poiGame != null && !poiGame.ref.equals(currentGame.ref)) {
                showAlertDifferentGame(context, poiGame, poi);
            }
        }
    });

    builder.setNegativeButton(getString(R.string.later), null);
    builder.setIcon(R.drawable.poi_unvisited);
    builder.create().show();
}

private void showAlertDifferentGame(final Context context, final Game game, final Poi poi) {
    AlertDialog.Builder builder = new AlertDialog.Builder(context);
    builder.setTitle(getString(R.string.game_switch_title));
    builder.setMessage(getString(R.string.game_switch_message) + " " + LanguageHelper.getGameTitle(game) + " ?");
    builder.setPositiveButton(R.string.yes, new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialog, int which) {
            Realm realm = Realm.getDefaultInstance();
            realm.beginTransaction();
            game.lastSeenPoi = poi.ref;
            realm.commitTransaction();

            SharedPreferencesHelper.saveString(context, Constants.PREF_SELECTED, game.ref);
            GeofenceService.updateGeoFences(game, context);
            checkCurrentActivity();
        }
    });
    builder.setNegativeButton(R.string.no, new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialog, int which) {
            checkCurrentActivity();
        }
    });
    builder.create().show();
}

private void checkCurrentActivity() {
    final Activity currentActivity = GeoFortApplication.getCurrentActivity();
    if (currentActivity instanceof MainActivity) {
        ((MainActivity) currentActivity).switchTab();
    } else {
        currentActivity.finish();
        new Handler().postDelayed(new Runnable() {
            @Override
            public void run() {
                try {
                    Log.d(Constants.DEBUG, "CurrentActivity: " +  currentActivity.toString());
                    ((MainActivity) currentActivity).switchTab();
                } catch (ClassCastException e) {
                    Log.e(Constants.EXCEPTION, e.getLocalizedMessage());
                }
            }
        }, 5000);
    }
}


private void alertNoticeOutOfRange() {
    new AlertDialog.Builder(this)
            .setTitle(R.string.error_location_not_close_enough_title)
            .setMessage(R.string.error_location_not_close_enough_alert)
            .setPositiveButton(R.string.ok, null)
            .setIcon(R.drawable.ic_launcher)
            .show();
}

private void warnUserNoLocationProviderSet() {
    new AlertDialog.Builder(this)
            .setTitle(R.string.error_location_not_available_title)
            .setMessage(R.string.error_location_services_not_available_text)
            .setPositiveButton(R.string.ok, new DialogInterface.OnClickListener() {
                @Override
                public void onClick(DialogInterface dialog, int which) {
                    // TODO no user location set?
                }
            })
            .setIcon(null)
            .show();
}

@Override
protected void onResume() {
    super.onResume();

    IntentFilter filterWithinPoi = new IntentFilter(Constants.NOTIFICATION_WITHIN_POI);
    filterWithinPoi.setPriority(2);
    registerReceiver(onNoticeWithinPoi, filterWithinPoi);

    IntentFilter filterOutOfRange = new IntentFilter(Constants.NOTIFICATION_LOCATION_OUT_OF_RANGE);
    filterOutOfRange.setPriority(2);
    registerReceiver(onNoticeOutOfRange, filterOutOfRange);

    IntentFilter filterLocationProviderOff = new IntentFilter(Constants.NOTIFICATION_LOCATION_PROVIDER_OFF);
    registerReceiver(onNoLocationProviderSet, filterLocationProviderOff);
}

@Override
protected void onPause() {
    super.onPause();

    unregisterReceiver(onNoticeWithinPoi);
    unregisterReceiver(onNoticeOutOfRange);
    unregisterReceiver(onNoLocationProviderSet);
}

}

Answer 1

你在 else 上做错了

private void checkCurrentActivity() {
    final Activity currentActivity = GeoFortApplication.getCurrentActivity();
    if (currentActivity instanceof MainActivity) {
        ((MainActivity) currentActivity).switchTab();
    } else {
        currentActivity.finish();
        new Handler().postDelayed(new Runnable() {
            @Override
            public void run() {
                try {
                    Log.d(Constants.DEBUG, "CurrentActivity: " +  currentActivity.toString());
                    ((MainActivity) currentActivity).switchTab();
                } catch (ClassCastException e) {
                    Log.e(Constants.EXCEPTION, e.getLocalizedMessage());
                }
            }
        }, 5000);
    }
}

在运行方法中，activity 不是 MainActivity，正如您之前检查过的那样。

Answer 2

拳头检查

if (activity instanceOf MainActivity){
    // do typecast here
}else{
    // you should which which instance you have 
}

这样你将摆脱 classCastException

将 Activity 转换为 MainActivity 时出现 ClassCastException

ClassCastException when casting Activity to MainActivity

java

android

classcastexception