Access codebehind variable in XAML

How can I access the public variable which in Sample.xaml.cs file like asp.net <%=VariableName%>?

There are a few ways to do this.

• Add your variable as a resource from codebehind:

   myWindow.Resources.Add("myResourceKey", myVariable);
  

  Then you can access it from XAML:

   <TextBlock Text="{StaticResource myResourceKey}"/>
  

  If you have to add it after the XAML gets parsed, you can use a DynamicResource above instead of StaticResource.

• Make the variable a property of something in your XAML. Usually this works through the DataContext:

   myWindow.DataContext = myVariable;
  

  or

   myWindow.MyProperty = myVariable;
  

  After this, anything in your XAML can access it through a Binding:

   <TextBlock Text="{Binding Path=PropertyOfMyVariable}"/>
  

  or

   <TextBlock Text="{Binding ElementName=myWindow, Path=MyProperty}"/>
  

For binding, if DataContext is not in use, you can simply add this to the constructor of the code behind:

this.DataContext = this;

Using this, every property in the code becomes accessible to binding:

<TextBlock Text="{Binding PropertyName}"/>

Another way is to just give a name to the root element of the XAML:

x:Name="root"

Since the XAML is compiled as a partial class of the code-behind, we can access every property by name:

<TextBlock Text="{Binding ElementName="root" Path=PropertyName}"/>

Note: access is only available to properties; not to fields. set; and get; or {Binding Mode = OneWay} are necessary. If OneWay binding is used, the underlying data should implement INotifyPropertyChanged.

For quick-and-dirty Windows in WPF, I prefer binding the DataContext of the Window to the window itself; this can all be done in XAML.

Window1.xaml

<Window x:Class="WpfApplication1.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    DataContext="{Binding RelativeSource={RelativeSource self}}"
    Title="Window1" Height="300" Width="300">
    <StackPanel>
        <TextBlock Text="{Binding Path=MyProperty1}" />
        <TextBlock Text="{Binding Path=MyProperty2}" />
        <Button Content="Set Property Values" Click="Button_Click" />
    </StackPanel>
</Window>

Window1.xaml.cs

public partial class Window1 : Window
{
    public static readonly DependencyProperty MyProperty2Property =
        DependencyProperty.Register("MyProperty2", typeof(string), typeof(Window1), new UIPropertyMetadata(string.Empty));

    public static readonly DependencyProperty MyProperty1Property =
        DependencyProperty.Register("MyProperty1", typeof(string), typeof(Window1), new UIPropertyMetadata(string.Empty));

    public Window1()
    {
        InitializeComponent();
    }

    public string MyProperty1
    {
        get { return (string)GetValue(MyProperty1Property); }
        set { SetValue(MyProperty1Property, value); }
    }

    public string MyProperty2
    {
        get { return (string)GetValue(MyProperty2Property); }
        set { SetValue(MyProperty2Property, value); }
    }

    private void Button_Click(object sender, RoutedEventArgs e)
    {
        // Set MyProperty1 and 2
        this.MyProperty1 = "Hello";
        this.MyProperty2 = "World";
    }
}

In the above example, note the binding used in the DataContext property on the Window, this says "Set your data context to yourself". The two text blocks are bound to MyProperty1 and MyProperty2, the event handler for the button will set these values, which will automatically propagate to the Text property of the two TextBlocks as the properties are Dependency Properties.

It is also worth noting that a 'Binding' can only be set on a DependencyProperty of a DependencyObject. If you want to set a non DependencyProperty (eg. a normal property) on an object in XAML, then you will have to use Robert's first method of using resources in the code behind.

myWindow.xaml

<Window
    ...
    <TextBlock Text="{ Binding Path=testString }" />
</Window>

myWindow.xaml.cs

public partial class myWindow: Window
{
    public string testString { get; set; } = "This is a test string";

    public myWindow()
    {
        DataContext = this;
        InitializeComponent();
    }
}

Important

• Set Datacontext
• testString MUST be public
• testString MUST be a property (have a get and set)