Set DataContext in XAML

I have this simple application that adds some items to a combobox:

public partial class Window1 : Window
    {
        private ObservableCollection<string> _dropDownValues = new ObservableCollection<string>();
        public ObservableCollection<string> DropDownValues
        {
            get { return _dropDownValues; }
            set { _dropDownValues = value; }
        }

        private string _selectedValue;
        public string SelectedValue
        {
            get { return _selectedValue; }
            set { _selectedValue = value; }
        }

        public Window1()
        {
            InitializeComponent();
            DataContext = this;

            DropDownValues.Add("item1");
            DropDownValues.Add("item1");
            DropDownValues.Add("item1");
            DropDownValues.Add("item1");
            DropDownValues.Add("item1");
            DropDownValues.Add("item1");
        }
    }

And here is the XAML file:

<Window x:Class="WpfApplication2.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" Height="300" Width="300">
    <StackPanel HorizontalAlignment="Left" Margin="10">
        <ComboBox
            Margin="0 0 0 5"
            ItemsSource="{Binding DropDownValues}"
            SelectedValue="{Binding SelectedValue}"        
            Width="150"/>     
    </StackPanel>
</Window>

Can someone show me how can I set the DataContext from the xaml file instead of initializing in the constructor ?

Thanks.

Just change the Window to bind DataContext to itself:

<Window x:Class="WpfApplication2.Window1"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="Window1" Height="300" Width="300"
        DataContext="{Binding RelativeSource={RelativeSource Self}}" ... />

I believe the DataContext in this scenario is implicit and does not have to be set since you are using the code behind. If you were using MVVM you would add a reference to that folder and class inside of you XAML markup and set the resource key equal to a value that can then be declared as the DataContext inside of a child elements DataContext property. But in your case (since you are not using MVVM) you shouldn't have to do that.