How do I display the first item in my ComboBox based on my dataBinding?

Question

Xaml:

<ComboBox Grid.Row="1"
                  Name="CmbClasse"
                  Grid.Column="3"
                  Margin="5,5,5,5"
                  ItemsSource="{Binding DataContext.Classeses}"
                  SelectedValuePath="ClasseId"
                  DisplayMemberPath="ClasseName"
                  SelectedValue="{Binding DataContext.CurrentSelectedPersonagem.IdClasse, Mode=TwoWay}"/>

When I open my application, the ComboBox do not have display any default item. But the item list is working, have all the items on it. Please help, if a image is needed just ask. Thanks.

Answer 1

Here is a method I use all the time.

Firstly, your View Model should have two properties, one to represent the collection, and the other to represent the selected item.

public IEnumerable<YourObject> MyObjects { get; private set; }
public YourObject SelectedObject { get; private set; }

Note: It would be a good idea to use an ObservableCollection for MyObjects, and also implement INotifyPropertyChanged. Use this only if you need to create brand new instances of your collection in the View Model.

Your ComboBox should then bind to these properties, like so:

<ComboBox ItemsSource="{Binding MyObjects}"
          SelectedItem="{Binding SelectedObject}"
          ... 
          />

Now, here comes the magic. When you create your collection, simply set the SelectedObject to be the FirstOrDefault item in the list.

private void LoadData()
{
    //TODO: Load the data into the collection

    //Set the first item
    this.SelectedObject = MyObjects.FirstOrDefault();
}

This will ensure that the first item is always selected. You do not need to implement INotifyPropertyChanged on the SelectedObject property unless you are planning on manually changing the value of this property in your View Model.