WPF DialogResult declaratively?

You can do this with an attached behavior to keep your MVVM clean. The C# code for your attached behavior might look something like so:

public static class DialogBehaviors{    private static void OnClick(object sender, RoutedEventArgs e)    {        var button = (Button)sender;        var parent = VisualTreeHelper.GetParent(button);        while (parent != null && !(parent is Window))        {            parent = VisualTreeHelper.GetParent(parent);        }        if (parent != null)        {            ((Window)parent).DialogResult = true;        }    }    private static void IsAcceptChanged(DependencyObject obj, DependencyPropertyChangedEventArgs e)    {        var button = (Button)obj;        var enabled = (bool)e.NewValue;        if (button != null)        {            if (enabled)            {                button.Click += OnClick;            }            else            {                button.Click -= OnClick;            }        }    }    public static readonly DependencyProperty IsAcceptProperty =        DependencyProperty.RegisterAttached(            name: "IsAccept",            propertyType: typeof(bool),            ownerType: typeof(Button),            defaultMetadata: new UIPropertyMetadata(                defaultValue: false,                propertyChangedCallback: IsAcceptChanged));    public static bool GetIsAccept(DependencyObject obj)    {        return (bool)obj.GetValue(IsAcceptProperty);    }    public static void SetIsAccept(DependencyObject obj, bool value)    {        obj.SetValue(IsAcceptProperty, value);    }}

You can use the property in XAML with the code below:

<Button local:IsAccept="True">OK</Button>

An alternative way is to use Popup Control

Try this tutorial.