OnRestoreInstanceState 在 Xamarin 中遇到问题

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事的时间。当 Activity 被发送到后台时，我似乎对用于保存值的方法有疑问。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......你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

I seem to have a problem with the methods applied in saving values when the Activity is being sent to the background.

你可以用这个Activity.OnRestoreInstanceState Method检查一下就知道：

This method is called after OnStart() when the activity is being re-initialized from a previously saved state, given here in savedInstanceState.

该方法在后台返回时不会被调用，只有在re-initialized后才会被调用。比如Recreate()方法会调用它。

所以这里在进入后台的时候，OnSaveInstanceState的方法是有效的。但是，OnRestoreInstanceState不会被调用。

现在如果你想存储一些数据并恢复背景和前景之间的视图，你可以使用 SharedPreferences in OnResume() 和 OnPause() of Activity.

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();
}

那么效果会显示：

OnRestoreInstanceState 在 Xamarin 中遇到问题

OnRestoreInstanceState got a problem in Xamarin

android

xamarin

onsaveinstancestate

onrestoreinstancestate