(注:在API 14中添加了官方API:见此答案https://stackoverflow.com/a/29786451/119733)

不要使用以前的(waqas716)答案。

由于对活动的静态引用，您将有内存泄漏问题。欲了解更多详情，请参阅以下链接http://android-developers.blogspot.fr/2009/01/avoiding-memory-leaks.html

为了避免这种情况，您应该管理活动引用。 在manifest文件中添加应用程序的名称:

<application
    android:name=".MyApp"
    ....
 </application>

你的应用类:

  public class MyApp extends Application {
        public void onCreate() {
              super.onCreate();
        }

        private Activity mCurrentActivity = null;
        public Activity getCurrentActivity(){
              return mCurrentActivity;
        }
        public void setCurrentActivity(Activity mCurrentActivity){
              this.mCurrentActivity = mCurrentActivity;
        }
  }

创建一个新活动:

public class MyBaseActivity extends Activity {
    protected MyApp mMyApp;

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mMyApp = (MyApp)this.getApplicationContext();
    }
    protected void onResume() {
        super.onResume();
        mMyApp.setCurrentActivity(this);
    }
    protected void onPause() {
        clearReferences();
        super.onPause();
    }
    protected void onDestroy() {        
        clearReferences();
        super.onDestroy();
    }

    private void clearReferences(){
        Activity currActivity = mMyApp.getCurrentActivity();
        if (this.equals(currActivity))
            mMyApp.setCurrentActivity(null);
    }
}

所以，现在不是为你的活动扩展Activity类，而是扩展MyBaseActivity。现在，你可以像这样从应用程序或活动上下文中获取当前活动:

Activity currentActivity = ((MyApp)context.getApplicationContext()).getCurrentActivity();

您可以使用这个类进行灵活的生命周期处理

用法:

    //Initialization
    val lifeCycleHandler = ActivityLifeCycleHandler<Activity>()

    //Detect only a specific type of activities
    val lifeCycleHandler = ActivityLifeCycleHandler<MainActivity>()

    //Get current activity
    val instance = lifeCycleHandler.currentReference

    //Get current activity state
    val state = lifeCycleHandler.currentState

    //Use listeners
    lifeCycleHandler.addStateChangeListener { newState ->
        //TODO: handle new state
    }

    lifeCycleHandler.addSpecificStateChangeListener(ActivityLifeCycleHandler.ActivityState.STARTED) {
        //TODO: handle new state
    }

    //Removable listeners
    val listener = { newState: Int ->

    }

    lifeCycleHandler.addStateChangeListener(listener)
    lifeCycleHandler.removeStateChageListener(listener)


    //Start listening
    App.app.registerActivityLifecycleCallbacks(lifeCycleHandler)

    //Stop listening
    lifeCycleHandler.releaseListeners()
    App.app.unregisterActivityLifecycleCallbacks(lifeCycleHandler)

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;
    }
}

(注:在API 14中添加了官方API:见此答案https://stackoverflow.com/a/29786451/119733)

不要使用以前的(waqas716)答案。

由于对活动的静态引用，您将有内存泄漏问题。欲了解更多详情，请参阅以下链接http://android-developers.blogspot.fr/2009/01/avoiding-memory-leaks.html

为了避免这种情况，您应该管理活动引用。 在manifest文件中添加应用程序的名称:

<application
    android:name=".MyApp"
    ....
 </application>

你的应用类:

  public class MyApp extends Application {
        public void onCreate() {
              super.onCreate();
        }

        private Activity mCurrentActivity = null;
        public Activity getCurrentActivity(){
              return mCurrentActivity;
        }
        public void setCurrentActivity(Activity mCurrentActivity){
              this.mCurrentActivity = mCurrentActivity;
        }
  }

创建一个新活动:

public class MyBaseActivity extends Activity {
    protected MyApp mMyApp;

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        mMyApp = (MyApp)this.getApplicationContext();
    }
    protected void onResume() {
        super.onResume();
        mMyApp.setCurrentActivity(this);
    }
    protected void onPause() {
        clearReferences();
        super.onPause();
    }
    protected void onDestroy() {        
        clearReferences();
        super.onDestroy();
    }

    private void clearReferences(){
        Activity currActivity = mMyApp.getCurrentActivity();
        if (this.equals(currActivity))
            mMyApp.setCurrentActivity(null);
    }
}

所以，现在不是为你的活动扩展Activity类，而是扩展MyBaseActivity。现在，你可以像这样从应用程序或活动上下文中获取当前活动:

Activity currentActivity = ((MyApp)context.getApplicationContext()).getCurrentActivity();

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:)

我在Kotlin中做了以下工作

Create Application Class Edit the Application Class as Follows class FTApplication: MultiDexApplication() { override fun attachBaseContext(base: Context?) { super.attachBaseContext(base) MultiDex.install(this) } init { instance = this } val mFTActivityLifecycleCallbacks = FTActivityLifecycleCallbacks() override fun onCreate() { super.onCreate() registerActivityLifecycleCallbacks(mFTActivityLifecycleCallbacks) } companion object { private var instance: FTApplication? = null fun currentActivity(): Activity? { return instance!!.mFTActivityLifecycleCallbacks.currentActivity } } } Create the ActivityLifecycleCallbacks class class FTActivityLifecycleCallbacks: Application.ActivityLifecycleCallbacks { var currentActivity: Activity? = null override fun onActivityPaused(activity: Activity?) { currentActivity = activity } override fun onActivityResumed(activity: Activity?) { currentActivity = activity } override fun onActivityStarted(activity: Activity?) { currentActivity = activity } override fun onActivityDestroyed(activity: Activity?) { } override fun onActivitySaveInstanceState(activity: Activity?, outState: Bundle?) { } override fun onActivityStopped(activity: Activity?) { } override fun onActivityCreated(activity: Activity?, savedInstanceState: Bundle?) { currentActivity = activity } } you can now use it in any class by calling the following: FTApplication.currentActivity()