WPF - Auto refresh combobox content

I got a sample mvvm app. The UI has a textbox, a button and a combobox. when I enter something in the textbox 开发者_StackOverflow社区and hit the button, the text I enter gets added to an observablecollection. The Combobox is bound to that collection. How do I get the combobox to display the newly added string automaticly?

As I understand correctly, you want to add an item and select it. Here is the example how it can be done using ViewModel and bindings.

Xaml:

<StackPanel>
    <TextBox Text="{Binding ItemToAdd}"/>
    <ComboBox ItemsSource="{Binding Items}" SelectedItem="{Binding SelectedItem}" />
    <Button Content="Add" Click="Button_Click"/>
</StackPanel>

ViewModel:

public class MainViewModel:INotifyPropertyChanged
{
    public ObservableCollection<string> Items { get; set; }

    public string ItemToAdd { get; set; }

    private string selectedItem;

    public string SelectedItem
    {
        get { return selectedItem; }
        set
        {
            selectedItem = value;
            OnPropertyChanged("SelectedItem");
        }
    }

    public void AddNewItem()
    {
        this.Items.Add(this.ItemToAdd);
        this.SelectedItem = this.ItemToAdd;
    }


    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual void OnPropertyChanged(string propertyName)
    {
        if (this.PropertyChanged != null)
        {
            this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

The MainViewModel has 3 properties (one for the TextBox and two other for the ComboBox) and the method AddNewItem without parameters.

The method can be triggered from a command, but there is no standard class for commands, so I will call it from the code-behind:

   ((MainViewModel)this.DataContext).AddNewItem();

So you must explicitly set an added item as selected after you add it to a collection.

Because the method OnItemsChanged of the ComboBox class is protected and can't be used.

If the ComboBox is bound to an ObservableCollection, the ComboBox will be updated as soon as the collection is changed.

That's the advantage of using an ObservableCollection - you don't need to do any extra coding to update the UI.

If this is not the behavior you're seeing, perhaps you can post some code/xaml.