OnRestoreInstanceState 在 Xamarin 中出现问题

Question

我正在开发一个闹钟应用程序，我的布局恰好包含一个 TimePicker 视图，用于设置用户希望提醒某件事的时间。当活动发送到后台时，我似乎对保存值所应用的方法有问题。编译器中的代码是干净的，没有错误，但是当我在智能手机上调试它时，我将应用程序发送到后台，然后当恢复它时，TimePicker 当前时间不会被这两种方法修改...您的时间和贡献是非常感谢

 class SecondActivity : AppCompatActivity
    {
      TimePicker timePicker2;
       int x=2;
       protected override void OnCreate(Bundle savedInstanceState)
        {
         base.OnCreate(savedInstanceState);
         //Timepicker definition
         timepicker1=this.FindViewById<TimePicker>(Resource.Id.timepicker1);
          //Setting the default selected time of the Timepicker via OnCreate
        timepicker1.CurrentHour=Java.Lang.Integer.ValueOf(x);

        }
     //This method supposedly overrides another method called OnSavedInstanceState and allows programmer to save values to it
      protected override void OnSaveInstanceState(Bundle savedInstanceState)
        {
            int y;
            y = 2;
         //Saving my value to Bundle savedInstanceState
            savedInstanceState.PutInt("value",y);
           //This super is being called but i dont know what it does
            base.OnSaveInstanceState(savedInstanceState);
        }
     //This method is supposed to remember all the values user saved before the Activity went into OnPause()
//Changed this from public to protected because i figured onsavedInstanceState has its parameters protected so unless its an inheritance, access to its members is forbidden
        protected override void OnRestoreInstanceState(Bundle savedInstanceState)
        {
            base.OnRestoreInstanceState(savedInstanceState);
            //Restore the time value from the SavedInstance state
            int c = savedInstanceState.GetInt("value");
           //Assign the value to The Timepicker
            timePicker2.CurrentHour=(Java.Lang.Integer.ValueOf(c));
        }
}````
What am i doing wrong? An additional alert dialog code to detect when activity goes into Onpause and OnRestore will greatly be appreciated

Answer 1

当活动发送到后台时，我似乎对保存值所应用的方法有问题。

你可以通过这个 Activity.OnRestoreInstanceState 方法检查一下就知道：

当 Activity 从之前保存的状态重新初始化时，此方法会在

OnStart()

之后调用，如

savedInstanceState

中所示。

^{（图片来自重新创建活动）}

从后台返回时不会调用该方法，只有重新初始化后才会调用。比如

Recreate()

方法会调用它。

因此，这里当进入后台时，

OnSaveInstanceState

方法就起作用了。但是，

OnRestoreInstanceState

不会被调用。

现在如果你想存储一些数据并恢复后台和前台之间的视图，你可以使用

SharedPreferences

中的

OnResume()

和

Activity

的OnPause()。

例如代码如下：

protected override void OnResume()
{
    base.OnResume();
    ISharedPreferences prefs = PreferenceManager.GetDefaultSharedPreferences(this);
    int value = prefs.GetInt("value", 0);
    timePicker1.CurrentHour = (Java.Lang.Integer.ValueOf(value));
}


protected override void OnPause()
{
    base.OnPause();
    ISharedPreferences prefs = PreferenceManager.GetDefaultSharedPreferences(this);
    ISharedPreferencesEditor editor = prefs.Edit();
    int y;
    y = 2;
    editor.PutInt("value", y);
    editor.Apply();
}

然后就会显示效果：