ComboBox SelectedItem 绑定不更新

Question

I'm a bit puzzled: this works:

<StackPanel Orientation="Horizontal" HorizontalAlignment="Right">
            <Label Content="Rol" />
            <ComboBox ItemTemplate="{StaticResource listRollen}"
                      Height="23" Width="150"
                      SelectedItem="{Binding Path=SelectedRol, UpdateSourceTrigger=PropertyChanged, Mode=TwoWay}"
                      ItemsSource="{Binding Path=allRollen, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" />
        </StackPanel>

and the property for SelectedRol is:

public TblRollen SelectedRol
    {
        get { return _selectedRol; }
        set
        {
            if (_selectedRol != value)
            {
                _selectedRol = value;
                OnPropertyChanged("SelectedRol");
            }
        }
    }

But this doesn't work:

<StackPanel Orientation="Horizontal" HorizontalAlignment="Right">
            <Label Content="Soort" />
            <ComboBox ItemTemplate="{StaticResource listSoorten}"
                      Height="23" Width="150"
                      ItemsSource="{Binding Path=allSoorten}"
                      SelectedItem="{Binding Path=SelectedProduct, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"/>
        </StackPanel>

with following property SelectedProduct:

public TblProduktSoorten SelectedProduct
    {
        get { return _selectedPSoort; }
        set
        {
            if (_selectedPSoort != value)
            {
                _selectedPSoort = value;
                OnPropertyChanged("SelectedProduct");
            }
        }
    }

somewhere in my code I set SelectedProduct = p.TblProduktSoorten and while debugging, I see the property gets set correctly...

Answer 1

Combobox inside a DataGrid?

If the combobox is in a DataGrid you must add this:

Mode=TwoWay, UpdateSourceTrigger=PropertyChanged

See this: https://stackoverflow.com/a/5669426/16940

Answer 2

This might be related to the fact that apparently attribute order does matter , in your second case the ItemsSource and SelectedItem declarations are swapped.

Answer 3

Try to use not selected item but value path look at the code sample

<ComboBox Name="projectcomboBox" ItemsSource="{Binding Path=Projects}" IsSynchronizedWithCurrentItem="True" DisplayMemberPath="FullName"
          SelectedValuePath="Name"  SelectedIndex="0"  Grid.Row="1" Visibility="Visible" Canvas.Left="10" Canvas.Top="24" Margin="11,6,13,10">
</ComboBox>

the binding property is

public ObservableCollection<Project> Projects
{
    get { return projects; }
    set
    {
        projects = value;
        RaisePropertyChanged("Projects");
    }
}

Answer 4

I don't know if you fixed it yet, but I encountered the same issue today. It was fixed by making sure the collection for selecteditems was an ObservableCollection.

Answer 5

If you set the SelectedProduct property when SelectedProduct is changed in the property changed event handler, you need to set this property asynchronously.

private void ViewModel_PropertyChanged(object sender, PropertyChangedEventArgs e)
{
    if (e.PropertyName == "SelectedProduct")
        App.Current.Dispatcher.InvokeAsync(() => SelectedProduct = somevalue);
}

Answer 6

My problem was caused by my own tired brain. Same symptom, maybe it will kick you into seeing your problem.

Setting the SelectedItem must be given an item in the List;! (duhh) Normally this happens naturally but I had a case I got a "Role" from another service (Same object type) and was trying to set it and expecting the combobox to change! ;(

instead of -

Roles = roles;
CurrentRole = role;

remember to do this -

Roles = roles;
CurrentRole = roles.FirstOrDefault(e=> e.ID == role.ID); //(System.Linq)

Answer 7

I think this problem is caused by the type of ItemSource and SelectedItem is mitchmatched .

For example, if the ItemSource is binded to a List of int and the SelectedItem is binded to a string . If you set selected item to null or empty string, the combobox cannot know what item is selected. So the combobox will show nothing.

Answer 8

This might be old but I have not seen the trick that did it for me; I had to add NotifyOnSourceupdate=true to my SelectedItem in the ComboBox

Answer 9

This had me stumped for a while inside a DataGrid, using SelectedItem. Everything was fine but I am deserializing the app state which loads the items and also has a selected item. The collection was there but the selected isn't actually visible until I used the Text="{Binding Path=Score.SelectedResult.Offset}"

<DataGridTemplateColumn.CellTemplate>
    <DataTemplate>
        <ComboBox ToolTip="Score offset results" 
          ItemsSource="{Binding Score.SearchResults,UpdateSourceTrigger=PropertyChanged}"                                                   
          SelectedItem="{Binding Score.SelectedResult, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
          Text="{Binding Path=Score.SelectedResult.Offset}"
          SelectedValuePath="Offset"
          DisplayMemberPath="Offset"/>
    </DataTemplate>
</DataGridTemplateColumn.CellTemplate>