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What i'm doing wrong?
Basic binding to Combobox ItemsSource.

What I have tried:

public partial class MainWindow : Window
        ObservableCollection<string> _items = new ObservableCollection<string> { "a1", "a2" };

        public ObservableCollection<string> Items


            get { return _items; }

            set { _items = value; }

        public MainWindow()
            var aa = a1;


       <ComboBox Name="a1" ItemsSource="{Binding Items}">

Updated 10-Apr-19 22:11pm

read another codeproject article
Step by Step WPF Data Binding with Comboboxes[^]

ItemsSource - is bound to the static resource array 'ColorListString' that we defined above as an application resource in the App.xaml file. This list of items is used to populate the Items collection of the ComboBox. This collection is used to generate the items that show up in the dropdown list.
DisplayMemberPath - is bound to the ValueString property of the ComboBoxItemString object, in the ItemsSource list. When an item is selected from the dropdown list, this is the value that is displayed to the user.
SelectedValuePath - is bound to ValueString property of the ComboBoxItemString object, in the ItemsSource list. When an item is selected from the dropdown list, this is the property used to get the value to set the SelectedItem value to.
SelectedValue - is bound using a property binding of "{Binding ColorString}". When an item is selected in the list, this is the property on the data object that is set to the value returned from the SelectedValuePath property.

<pre><combobox itemssource="{StaticResource ColorListString}">
            SelectedValue="{Binding ColorString}" /></combobox>
This answer is way after the posting and I hope you figured it out by now, but when you're binding without a source the default source is the DataContext property. In this example your DataContext property has not been set yet. The easiest fix in this example is to do this:

public MainWindow()
    DataContext = this;

I personally do not recommend a view being it's own DataContext, but if you're going to do it you should also make it's exposed property you're binding to a DependencyProperty.

You need to implement INotifyPropertyChanged on you viewmodel (class with your observable collection).

Once that is done you'll use the eventhandler provided by the interface to let your GUI know that whenever your collection is updated.

Typcally it looks like this.

public class YourClass : INotifyPropertyChagned
    private ObservableCollection<string> _collectionOfStrings;
    public ObservableCollection<string> CollectionOfStrings
        get => _collectionOfStrings
            if (value != _collectionOfStrings)
                _listOfStrings = value;

    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual void OnPropertyChanged([CallerMemberName] string propertyName =
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));

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