WPF binding behavior

Question

I have page like this ...

<Page x:Class="WPFTestRig.Page1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="Page1">
<Grid>
    <StackPanel>
        <ComboBox Name="myBox" ItemsSource="{Binding Path=MyCollection}" DisplayMemberPath="Name" IsSynchronizedWithCurrentItem="True" 
                  SelectedItem="{Binding Path=SelectedEntryValue}" SelectedValuePath="Name" SelectedValue="{Binding Path=SelectedEntryValue}"/>
    </StackPanel>

</Grid>
</Page>

with code behind as

 public partial class Page1 : Page
{
    private List<Entry> _myCollection;
    private string _selectedEntryValue;
    public Page1()
    {
        InitializeComponent();
        _myCollection = new List<Entry>();
        _myCollection.Add(new Entry { Name = "Test1", Id = 1 });
        _myCollection.Add(new Entry { Name = "Test2", Id = 2 });
        _myCollection.Add(new Entry { Name = "Test3", Id = 3 });

        _selectedEntryValue = "Test3";

        myBox.DataContext = this;
    }

    public List<Entry> MyCollection
    {
        get {
            return _myCollection;
        }
    }
    public string SelectedEntryValue
    {
        get {
            return _selectedEntryValue;
        }
        set { 
            _selectedEntryValue = value ;
        }
    }

}

public class Entry
{
    public string Name { get; set; }
    public int Id { get; set; }
}

when i put a break point on set property of SelectedEntryValue property, i see it gets called twice, once with the string of the type name like (MyTestApp.Entry) and then the actual selected value

can someone point out what i should be doing for it to work right ?

many thanks

Answer 1

Your problem is that you accidentally bound both SelectedItem and SelectedValue.

You wrote (reformatted for readability):

<ComboBox Name="myBox" ... SelectedValuePath="Name" ...
  SelectedItem="{Binding Path=SelectedEntryValue}"
  SelectedValue="{Binding Path=SelectedEntryValue}" />

Remove the SelectedItem binding and you will get the behavior you expect.

Answer 2

You're seeing that behavior because you bind it to both SelectedItem and SelectedValue, thus it executes twice. The first time it is bound it appears the displayed property is not being used yet.