一个相当简单的解决方案是创建一个单例管理器类，你可以在其中存储一个或多个活动的引用，或者你想在整个应用程序中访问的任何其他东西。

调用UberManager.getInstance()。setMainActivity(activity);在主活动的onCreate中。

.getMainActivity调用UberManager.getInstance () ();在应用程序的任何地方检索它。(我使用这个能够使用吐司从一个非UI线程。)

确保您添加了对UberManager.getInstance().cleanup()的调用;当你的应用程序被销毁时。

import android.app.Activity;

public class UberManager
{
    private static UberManager instance = new UberManager();

    private Activity mainActivity = null;

    private UberManager()
    {

    }

    public static UberManager getInstance()
    {
        return instance;
    }

    public void setMainActivity( Activity mainActivity )
    {
        this.mainActivity = mainActivity;
    }

    public Activity getMainActivity()
    {
        return mainActivity;
    }

    public void cleanup()
    {
        mainActivity = null;
    }
}

就我个人而言，我是按照“Cheok Yan Cheng”说的去做的，但我使用了一个“列表”来对我所有的活动进行“备份”。

如果你想检查哪个是当前活动，你只需要得到列表中的最后一个活动类。

创建一个扩展“application”的应用程序，这样做:

public class MyApplication extends Application implements Application.ActivityLifecycleCallbacks,
EndSyncReceiver.IEndSyncCallback {

private List<Class> mActivitiesBackStack;
private EndSyncReceiver mReceiver;
    private Merlin mMerlin;
    private boolean isMerlinBound;
    private boolean isReceiverRegistered;

@Override
    public void onCreate() {
        super.onCreate();
        [....]
RealmHelper.initInstance();
        initMyMerlin();
        bindMerlin();
        initEndSyncReceiver();
        mActivitiesBackStack = new ArrayList<>();
    }

/* START Override ActivityLifecycleCallbacks Methods */
    @Override
    public void onActivityCreated(Activity activity, Bundle bundle) {
        mActivitiesBackStack.add(activity.getClass());
    }

    @Override
    public void onActivityStarted(Activity activity) {
        if(!isMerlinBound){
            bindMerlin();
        }
        if(!isReceiverRegistered){
            registerEndSyncReceiver();
        }
    }

    @Override
    public void onActivityResumed(Activity activity) {

    }

    @Override
    public void onActivityPaused(Activity activity) {

    }

    @Override
    public void onActivityStopped(Activity activity) {
        if(!AppUtils.isAppOnForeground(this)){
            if(isMerlinBound) {
                unbindMerlin();
            }
            if(isReceiverRegistered){
                unregisterReceiver(mReceiver);
            }
            if(RealmHelper.getInstance() != null){
                RealmHelper.getInstance().close();
                RealmHelper.getInstance().logRealmInstanceCount("AppInBackground");
                RealmHelper.setMyInstance(null);
            }
        }
    }

    @Override
    public void onActivitySaveInstanceState(Activity activity, Bundle bundle) {

    }

    @Override
    public void onActivityDestroyed(Activity activity) {
        if(mActivitiesBackStack.contains(activity.getClass())){
            mActivitiesBackStack.remove(activity.getClass());
        }
    }
    /* END Override ActivityLifecycleCallbacks Methods */

/* START Override IEndSyncCallback Methods */
    @Override
    public void onEndSync(Intent intent) {
        Constants.SyncType syncType = null;
        if(intent.hasExtra(Constants.INTENT_DATA_SYNC_TYPE)){
            syncType = (Constants.SyncType) intent.getSerializableExtra(Constants.INTENT_DATA_SYNC_TYPE);
        }
        if(syncType != null){
            checkSyncType(syncType);
        }
    }
    /* END IEndSyncCallback Methods */

private void checkSyncType(Constants.SyncType){
    [...]
    if( mActivitiesBackStack.contains(ActivityClass.class) ){
         doOperation()     }
}

}

在我的例子中，我使用了“应用程序”。ActivityLifecycleCallbacks”:

Bind/Unbind Merlin Instance (used to get event when the app lose or get connection, for example when you close mobile data or when you open it). It is useful after the "OnConnectivityChanged" intent action was disabled. For more info about MERLIN see: MERLIN INFO LINK Close my last Realm Instance when the application is closed; I will init it inside a BaseActivity wich is extended from all others activities and which has a private RealmHelper Instance. For more info about REALM see: REALM INFO LINK For instance I have a static "RealmHelper" instance inside my "RealmHelper" class which is instantiated inside my application "onCreate". I have a synchronization service in which I create I new "RealmHelper" because Realm is "Thread-Linked" and a Realm Instance can't work inside a different Thread. So in order to follow Realm Documentation "You Need To Close All Opened Realm Instances to avoid System Resources Leaks", to accomplish this thing I used the "Application.ActivityLifecycleCallbacks" as you can see up. Finally I have a receiver wich is triggered when I finish to synchronize my application, then when the sync end it will call the "IEndSyncCallback" "onEndSync" method in which I look if I have a specific Activity Class inside my ActivitiesBackStack List because I need to update the data on the view if the sync updated them and I could need to do others operations after the app sync.

以上就是全部内容，希望对大家有所帮助。见u:)

getCurrentActivity()也在ReactContextBaseJavaModule中。 (因为这个问题最初被问到，许多Android应用程序也有ReactNative组件-混合应用程序。)

ReactNative中的类ReactContext有一整套逻辑来维护在getCurrentActivity()中返回的mCurrentActivity。

注:我希望getCurrentActivity()在Android应用程序类中实现。

知道ActivityManager管理活动，所以我们可以从ActivityManager获取信息。我们得到当前的前景运行活动

ActivityManager am = (ActivityManager)context.getSystemService(Context.ACTIVITY_SERVICE);
ComponentName cn = am.getRunningTasks(1).get(0).topActivity;

更新2018/10/03 getRunningTasks()已弃用。请参阅下面的解决方案。

此方法在API级别21中已弃用。 从Build.VERSION_CODES开始。LOLLIPOP，这种方法不再适用于第三方应用程序:以文档为中心的最近记录的引入意味着它可能会向调用者泄露人员信息。为了向后兼容，它仍然会返回它的数据的一个小子集:至少是调用者自己的任务，可能还有一些已知不敏感的其他任务，比如home。

一个相当简单的解决方案是创建一个单例管理器类，你可以在其中存储一个或多个活动的引用，或者你想在整个应用程序中访问的任何其他东西。

调用UberManager.getInstance()。setMainActivity(activity);在主活动的onCreate中。

.getMainActivity调用UberManager.getInstance () ();在应用程序的任何地方检索它。(我使用这个能够使用吐司从一个非UI线程。)

确保您添加了对UberManager.getInstance().cleanup()的调用;当你的应用程序被销毁时。

import android.app.Activity;

public class UberManager
{
    private static UberManager instance = new UberManager();

    private Activity mainActivity = null;

    private UberManager()
    {

    }

    public static UberManager getInstance()
    {
        return instance;
    }

    public void setMainActivity( Activity mainActivity )
    {
        this.mainActivity = mainActivity;
    }

    public Activity getMainActivity()
    {
        return mainActivity;
    }

    public void cleanup()
    {
        mainActivity = null;
    }
}

使用is操作符或其否定形式!is执行运行时检查，确定对象是否符合给定类型:

if (this !is OneActivity) {
// do something
} else if (this !is TwoActivity) {
// do something 2
}