显示2个项目时WPF绑定的列表框错误

Question

I have a WPF listbox in my window. In the Load event of the window, i create a List(of Object) and I added some items. At application starts or debug, I can see items. If I add 1 item on the list, i correctly see 1 only item. If I add 3 or more items, i correctly see 3 or more items. If I add 2 only items, i see 1 only item. Why?

Here is my WPF code

<Window x:Class="Cacatua.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:local="clr-namespace:Cacatua;assembly=" >

    <Grid>
        <ListBox Name="lbSearch" ItemsSource="{Binding}" />
    </Grid>
</Window>

And here is my code-behind (same assembly, in Cacatua namespace):

Private myLstSearch As List(Of Object)

Private Sub Window_Loaded(sender As System.Object, e As System.Windows.RoutedEventArgs) Handles MyBase.Loaded
     myLstSearch = New List(Of Object)
     lbSearch.ItemsSource = myLstSearch
     Dim myMedia1 as Media1

     myMedia1 = New Media1("IdMedia1-A")
     myLstSearch.Add(myMedia1)

     myMedia1 = New Media1("IdMedia1-B")
     myLstSearch.Add(myMedia1)
End Sub

where Media1 is a simple class that contains a string

Public Class Media1
    Private myIdTitolo As String
    Public ReadOnly Property IDTitolo As String
        Get
            Return (myIdTitolo)
        End Get
    End Property
    Public Sub New(str As String)
        myIdTitolo = str
    End Sub
End Class

With this code, I would see a list with this output (there is no datatemplate): Cacatua.Media1 Cacatua.Media1

but I see only Cacatua.Media1

I think it's a bug. But am I the first with this problem?

Answer 1

You've got the right idea, but the problem is your ItemsSource doesn't know when to update since you're not using an ObservableCollection . Also there is a timing issue between rendering and loading the window, and I think this has to do with the fact you aren't properly binding your items source.

For starters, try changing the type of myLstSearch to ObservableCollection(Of Media1) .

Also, a better way to do this would be to databind it from the XAML directly, so your code-behind would be something like:

Public property MyListSearch As ObservableCollection(Of Media1)

Then your XAML would look like:

<Window x:Class="Cacatua.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:Cacatua;assembly=">

    <Grid>
        <ListBox Name="lbSearch" ItemsSource="{Binding Path=MyListSearch}" />
    </Grid>
</Window>

That way, you can simply initialize MyListSearch in your window constructor, and then add elements to it whenever, while your view will automatically update.