java - 在LifecycleObserver中调用mainActivity的方法

Question

我有麻烦了。

我想从我的 LifeCycleManager(它是一个 LifecycleObserver)调用我的 MainActivity 方法并执行简单的 XML 修改。但是那次崩溃是因为我正在尝试访问 XML 值并且 main_activity.xml 尚未完全创建

首先这是我的 LifeCycleManager :

class LifeCycleManager(context: Context) : LifecycleObserver {

companion object {
    var notif = NotificationManager()
    var onForeground = false
    var main = MainActivity()

    // If we are on MainActivity return true , otherwise return false
    fun isOnHomeController(context: Context?): Boolean {

        if (context == null || context !is MainActivity)
            return false

        return true
    }


var mContext = context

// WHEN THE APP BECOME ACTIVE
@OnLifecycleEvent(Lifecycle.Event.ON_START)
fun appComeBackFromBackground() {
    onForeground = true
    notif.cancelAllLocalNotifications(mContext)

    if (isOnHomeController(mContext)) {
        // Call the refresh dialog and print it
        main.appComeBackFromBackground("refresh", null)
    }
}
}

这是我的 MainActivity 方法:

fun appComeBackFromBackground(status: String?, elementsadded: Int?)
{
Log.e("enterForeground", "App come back in Foreground")
if (status == null) return

when (status)
{
    "refresh" ->{
        val text = findViewById<TextView>(R.id.refreshtext)
        text.setText("test")
    }
    else -> {
        return
    }

}
}

如您所见，当我的 MainActivity Start 和 Lifecycle 获取事件并直接进入我的 appComeBackFromBackground() 方法时。在其中我调用了我的 MainActivity 方法，我想在其中修改 activity_main.xml 中的元素

论文崩溃:

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.mControllers.MainActivity}: java.lang.RuntimeException: Failed to call observer method

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.Window$Callback android.view.Window.getCallback()' on a null object reference

请问我该怎么办？我真的需要这样做(从 LifecycleObserver 到 MainActivity)。谢谢

编辑:

我试图像这样延迟调用 MainActivity 的方法:

Handler().postDelayed({
        main.appComeBackFromBackground("refresh", null)
    }, 5000)

即使加载了 MainActivity 布局，它也会崩溃

Answer 1

我正在用 Java 写这个，(如果您不想将数据保存在首选项或存储中，这是方法)

应用类:

public class TestApplication extends Application implements ActivityLifecycleCallbacks {
    private static String mStringToSet;
    
    @Override
    public void onCreate() {
        super.onCreate();
        //App is not from background, a new instance of your app           is created 
        mStringToSet="new_instance";
        registerActivityLifecycleCallbacks(this);
    }

    public static String getStringToSet() {
        return mStringToSet;
    }

  
    @Override
    public void onActivityDestroyed(Activity activity) {
        if(activity instanceof MainActivity){
        //This is only called when the activity is destroyed not the application, so if the context is your desired activity then set the string here
            mStringToSet="refresh";
        }
    }

   //Implement other life cycle methods** 

  

在您的 Activity 中:

public class MainActivity extends AppCompatActivity {
    private final String TAG="ACTIVITY";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);


        if("refresh".equals(TestApplication.getStringToSet())){
            Toast.makeText(this,"From Background",Toast.LENGTH_SHORT).show();
            (TextView)findViewById(R.id.YOUR_TEXT_VIEW).setText("refresh")
        }else{
            Log.d(TAG,TestApplication.getStringToSet());
            Toast.makeText(this,"Not from background",Toast.LENGTH_SHORT).show();
           (TextView)findViewById(R.id.YOUR_TEXT_VIEW).setText("new_instance")
        }

    }
}
     //Implement other life cycle methods
}