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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,用于设置用户希望被提醒某事的时间。当 Activity 被发送到后台时,我似乎对保存值的方法有问题。编译器中的代码很干净,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,这两种方法不会修改 TimePicker 当前时间......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
4

1 回答 1

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当 Activity 被发送到后台时,我似乎对保存值的方法有问题。

您可以使用此Activity.OnRestoreInstanceState 方法进行检查以了解:

OnStart()当活动从先前保存的状态重新初始化时调用此方法,在此处给出savedInstanceState

在此处输入图像描述

从后台返回时不会调用此方法,只有在重新初始化后才会调用。比如Recreate()方法会调用它。

因此,这里进入后台时,该OnSaveInstanceState方法有效。但是,OnRestoreInstanceState不会被调用。

现在,如果您想处理一些数据并恢复背景和前景之间的视图,您可以使用SharedPreferencesinOnResume()ActivityOnPause()

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();
}

然后效果会显示:

在此处输入图像描述

于 2020-10-13T02:37:13.380 回答