[Solved] Updating DataSource loses display of selected item

[Ryan]

Hi,

I have run into some strange behaviour, when changing the DataSource driving the RadLoopingList.

Steps:

1. Change the selected item to number 10 (image 1.png)
2. Press the application bar button, which will recreate the DataSource.
3. Observe that the LoopingList jumps to the very top, and the selected item is not visible (image 2.png).
4. Press the application bar button.
5. Observe the selected item jumps to the center as expected.

<telerikPrimitives:RadLoopingList
    ItemWidth="120"
    ItemHeight="120"
    Width="120"
    IsCentered="True"
    DataSource="{Binding DataSource}"
    SelectedIndex="{Binding SelectedIndex, Mode=TwoWay}"/>

public partial class MainPage : PhoneApplicationPage, INotifyPropertyChanged
{
    LoopingListDataSource dataSource;
    int selectedIndex = -1;

    public MainPage()
    {
        InitializeComponent();
        DataContext = this;

        CreateDataSource();
    }

    public LoopingListDataSource DataSource
    {
        get { return dataSource; }
        set { dataSource = value; NotifyPropertyChanged("DataSource"); }
    }

    public int SelectedIndex
    {
        get { return selectedIndex; }
        set { selectedIndex = value; NotifyPropertyChanged("SelectedIndex"); }
    }

    private void CreateDataSource()
    {
        DataSource = new LoopingListDataSource(1000);

        dataSource.ItemNeeded += (sender, args) =>
        {
            args.Item = new LoopingListDataItem();
        };

        dataSource.ItemUpdated += (sender, args) =>
        {
            args.Item.Text = args.Index.ToString();
        };
    }

    private void Button_Click(object sender, EventArgs e)
    {
        CreateDataSource();
    }

    public event PropertyChangedEventHandler PropertyChanged;
    private void NotifyPropertyChanged(string propertyName)
    {
        if (null != PropertyChanged)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

So it seems that the problem only occurs the first time the DataSource is swapped, and only after the selected index was changed.

Any help is much appreciated in what helping resolve this problem

Thanks
Ryan

[Ryan]

Image attached.

[Ryan]

Any updates on this?

I have a sample project however this forum only lets me attach pictures...

[Dimitrina]

Hi Ryan,

We need some more time to further investigate it. I will write again with our findings. Please don't hesitate to contact us in  case you have any additional questions.

Regards,
Dimitrina
Telerik

 

 

[Ryan]

Hi Dimitrina,

Let me know if there is anything else you need to help me with this problem. I have a sample project which reproduces the behaviour I can provide.

Thanks
Ryan

[Rosy Topchiyska]

Hi Ryan,

We have successfully reproduced this behavior. You will have to call the LoopingListDataSource.UpdateLayout() method when you change the DataSource:

private void CreateDataSource()
{
    this.DataSource = new LoopingListDataSource(1000);

    this.dataSource.ItemNeeded += (sender, args) =>
    {
        args.Item = new LoopingListDataItem();
    };

    this.dataSource.ItemUpdated += (sender, args) =>
    {
        args.Item.Text = args.Index.ToString();
    };

    this.dataSource.UpdateLayout();
}

I hope this helps and sorry for the delay. Please, do not hesitate to contact us if you have any other questions.

Regards,
Rosy Topchiyska
Telerik

 

 

[Ryan]

Thanks Rosy, your work-around performs perfectly!