Xamarin中的OnRestoreInstanceState出现问题

编程问答 2022-06-09

问题描述

我正在使用一个警报应用程序，而我的布局恰好包含一个TimePicker View，用于设置用户希望被提醒的时间。当将“活动”发送到后台时，保存值所应用的方法似乎出现问题。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，然后在恢复它时，TimePicker当前时间未被这两种方法修改...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

解决方法

当“活动”发送到后台时，我似乎对保存值所采用的方法存在疑问。

您可以通过此 Activity.OnRestoreInstanceState Method 查看以下信息：

从先前保存的状态（在OnStart()中给出的状态开始重新初始化活动时，在savedInstanceState之后调用此方法。

enter image description here

从后台返回时将不会调用此方法，只有在重新初始化后才能调用此方法。例如Recreate()方法将调用它。

因此，此处进入后台时，OnSaveInstanceState方法有效。但是，OnRestoreInstanceState将不会被调用。

现在，如果您想存储一些数据并恢复背景和前景之间的视图，则可以在活动的SharedPreferences和OnResume()中使用OnPause()。 / p>

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();
}

然后效果将显示：

enter image description here