ListView不更新（C＃）

Question

I am doing a simple test because I need to learn about the ListView. I've done a lot of searching and there is a LOT out there but all of it trying to do more than just the basics. So to understand the concept I've done a simple program and listed it below.

Everything works - except when i rotate the phone. I understand that it will destroy the Activity and I need to re-create the listview and adapter. What I don't understand is - why my list of strings is also "destroyed".

Looking at my example - the weekdays will be there after rotation. But the list of click-times will not !! What would be the right way to use the listview in my case? I'm not trying to do complicated row views or custom adapters. I'll go with the basics. Thanks !

namespace NewListViewTest
{
    [Activity(Label = "NewListViewTest", MainLauncher = true)]
    public class MainActivity : Activity
    {
        Button StartScan;
        Button StopScan;
        TextView Filter;
        ListView IBeaconActivities;
        List<string> dataList;
        ArrayAdapter<string> dataAdapter;

        protected override void OnCreate(Bundle savedInstanceState)
        {
            base.OnCreate(savedInstanceState);

            // Set our view from the "main" layout resource
            SetContentView(Resource.Layout.Main);

            dataList = new List<string>();
        }

        protected override void OnStart()
        {
            base.OnStart();
            StartScan = FindViewById<Button>(Resource.Id.startScan);
            StartScan.Click += StartScan_Click;

            StopScan = FindViewById<Button>(Resource.Id.stopScan);
            Filter = FindViewById<TextView>(Resource.Id.filter);
            IBeaconActivities = FindViewById<ListView>(Resource.Id.beaconActivities);

            dataAdapter = new ArrayAdapter<string>(this, Android.Resource.Layout.SimpleListItem1, dataList);
            IBeaconActivities.Adapter = dataAdapter;

            dataList.Add("Monday");
            dataList.Add("Tuesday");
            dataList.Add("Wednesday");
            dataList.Add("Thursday");
            dataList.Add("Friday");
            dataList.Add("Saturday");
            dataList.Add("Sunday");

            DataWasUpdated();
        }

        public void DataWasUpdated()
        {
            dataAdapter.Clear();
            dataAdapter.AddAll(dataList);

            dataAdapter.NotifyDataSetChanged();
        }

        private void StartScan_Click(object sender, System.EventArgs e)
        {
            dataList.Add("New item at: " + DateTime.Now.ToString("hh:mm:ss"));
            DataWasUpdated();
        }
    }
}

Answer 1

ListView not updating (c#)

You could read the Android Activity Lifecycle document, when you rotate the phone, your Activity will be destroyed and recreate. You could add a log to see more information, for example :

protected override void OnPause()
{
    base.OnPause();
    Log.Error(Tag, "OnPause");
}

protected override void OnResume()
{
    base.OnResume();
    Log.Error(Tag, "OnResume");
}

protected override void OnSaveInstanceState(Bundle outState)
{
    base.OnSaveInstanceState(outState);
    Log.Error(Tag, "OnSaveInstanceState");
}

protected override void OnRestoreInstanceState(Bundle savedInstanceState)
{
    base.OnRestoreInstanceState(savedInstanceState);
    Log.Error(Tag, "OnRestoreInstanceState");
}

protected override void OnDestroy()
{
    base.OnDestroy();
    Log.Error(Tag, "OnDestroy");
}

......

When you rotate your phone, you could see following information :

That's why your ListView will be destroyed.

Solution :

Add a ConfigurationChanges attribute in your Activity :

[Activity(Label = "ListActivity", 
    ConfigurationChanges = Android.Content.PM.ConfigChanges.Orientation | Android.Content.PM.ConfigChanges.ScreenSize)]
public class ListActivity : Activity

Then, when you rotate your phone only execute the OnConfigurationChanged method :

E/Activity (17410): OnConfigurationChanged

Your Activity won't be created and your New item will still exist.