Question

我有麻烦了。

我想从LifeCycleManager（这是一个LifecycleObserver）中调用MainActivity的方法，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：

public function inicio()
    {

        $pageInfo = 
        [
            'page_title'      => 'Inicio',
            'menu_active'     => 'Inicio',
            'submenu_active' => '',
        ];

        $globals = Globals::all();

        $web_name = $globals->where('name', 'Nombre del restaurante')->first();
        $web_description = $globals->where('name', 'Descripcion en google del restaurante')->first();
        $restaurant_bio = $globals->where('name', 'Biografia del restaurante')->first();
        $booking_phone = $globals->where('name', 'Télefono de reserva')->first();
        $client_mail = $globals->where('name', 'Email de contacto')->first();
        $full_address = $globals->where('name', 'Dirección del restaurante')->first();
        $city_zip_address = $globals->where('name', 'Código postal y ciudad')->first();

        $config = compact('web_name', 'web_description');

        $sliders = Slider::all();


        return view('inicio.index', compact('pageInfo', 'config', 'sliders', 'web_name'));
    }

这是我的MainActivity方法：

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)
    }
}
}

如您所见，当MainActivity启动时，我的生命周期获取事件并直接进入appComeBackFromBackground（）方法。在其中调用我的MainActivity方法，该方法是要从activity_main.xml

修改元素的地方

论文崩溃：

java.lang.RuntimeException：无法启动活动ComponentInfo {com.mControllers.MainActivity}：java.lang.RuntimeException：无法调用观察者方法

原因：java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法“ android.view.Window $ Callback android.view.Window.getCallback（）”

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

编辑：

我试图像这样延迟地调用MainActivity的方法：

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
    }

}
}

即使加载了MainActivity布局，它也会崩溃

Answer 1

我是用Java编写的，（如果您不想将数据保存在首选项或存储中，则这是一种方法）

应用程序类别：

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**

您的活动中：

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
}

在LifecycleObserver中调用mainActivity的方法

1 个答案: