Adding listbox items doesn't work in xamarin forms

Question

In xamarin forms development , adding items to listbox doesn't work well.

MainPage.xaml

  <ListBox  x:Name="vrlist_panel">
        <ListBox.ItemContainerStyle>
            ....
        </ListBox.ItemContainerStyle>

        <ListBox.ItemTemplate>
            <DataTemplate>
                <Grid Margin="0">
                    <Grid.ColumnDefinitions>
                        <ColumnDefinition Width="1*"></ColumnDefinition>
                        <ColumnDefinition Width="1*"></ColumnDefinition>
                    </Grid.ColumnDefinitions>
                    <Grid.RowDefinitions>
                        <RowDefinition Height="1*"></RowDefinition>
                    </Grid.RowDefinitions>

                    <Border Grid.Column="0" Grid.Row="0">
                        <Image Source="{Binding leftImg}" Height="100" Margin="14,2,13,20"></Image>
                    </Border>
                    <Border Grid.Column="1" Grid.Row="0">
                        <Image Source="{Binding rightImg}" Height="100" Margin="14,2,13,20"></Image>
                    </Border>
                </Grid>
            </DataTemplate>
        </ListBox.ItemTemplate>

  </ListBox>

MainPage.xaml.cs

public class VRDataModel
{
    public string leftImg { get; set; }

    public string rightImg { get; set; }
}


public partitial class MainPage : Page , 
                                    Autodesk.Revit.UI.IDockablePaneProvider
{
         ....
     private static ObservableCollection<VRDataModel> vrImgs = new 
                                       ObservableCollection<VRDataModel>();
         ....
}


    ...
vrlist_panel.ItemsSource = vrImgs;
    ...

Here is entire code. But even though vrImgs is valid value, the value of vrlist_panel.ItemsSource is null on runtime and it causes exception. I have been trying to fix this issue for several days but couldn't find the reason. How should I do?

Answer 1

Your example is incomplete but if you are getting a NullReferenceException when trying to set the ItemsSource property, you are probably not calling the InitializeComponent() method prior to setting the property:

public partial class MainPage : Page
{
    public MainPage()
    {
        InitializeComponent();
        ...
        vrlist_panel.ItemsSource = vrImgs;
    }
}