C# WPF PRISM - Make UserControl Draggable

Question

I already found a solution (How to make a user control draggable on screen like a window), but it doesn't work the way i wanted. In this solution only the content of the UserControl is draggable, but i open my UserDialog with the ShowDialog method, so the UserControl is a seperate Dialog (https://prismlibrary.com/docs/wpf/dialog-service.html).

Is there any equivalent to the DragMove() method for the UserControl?

Answer 1

I don't know if I understood correctly, but you want a behavior that when a user control is dragged you want the parent window to be dragged. So here it is :

public class DragParentWindowBehavior : Behavior<UserControl>
    {
        private Window parentWindow;

        protected override void OnAttached()
        {
            AssociatedObject.Loaded += AssociatedObject_Loaded;
            AssociatedObject.Unloaded += AssociatedObject_Unloaded;
            AssociatedObject.PreviewMouseLeftButtonDown += AssociatedObject_MouseLeftButtonDown;
        }

        private void AssociatedObject_Unloaded(object sender, RoutedEventArgs e)
        {
            parentWindow = null;
        }

        private void AssociatedObject_Loaded(object sender, RoutedEventArgs e)
        {
           //We get the parent window here. because the behavior is attached to the view way before it is shown.
            parentWindow = Window.GetWindow(AssociatedObject);
        }

        private void AssociatedObject_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
        {
            parentWindow?.DragMove();
        }

        protected override void OnDetaching()
        {
            AssociatedObject.PreviewMouseLeftButtonDown -= AssociatedObject_MouseLeftButtonDown;
            AssociatedObject.Loaded -= AssociatedObject_Loaded;
            AssociatedObject.Unloaded -= AssociatedObject_Unloaded;

            parentWindow = null;
        }
    }

This is how you use it in XAML :

<UserControl x:Class="Prism1.Modules.ModuleName.Views.DraggableControl"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             xmlns:local="clr-namespace:Prism1.Modules.ModuleName.Views" 
             xmlns:Behaviors="http://schemas.microsoft.com/xaml/behaviors" 
             xmlns:mvvm="clr-namespace:Prism1.Core.Mvvm;assembly=Prism1.Core"
             mc:Ignorable="d" 
             d:DesignHeight="450" d:DesignWidth="800">
    <Behaviors:Interaction.Behaviors>
        <mvvm:DragParentWindowBehavior></mvvm:DragParentWindowBehavior>
    </Behaviors:Interaction.Behaviors>
    <Grid x:Name="LayoutRoot" Margin="5">
        <Grid.RowDefinitions>
            <RowDefinition />
            <RowDefinition Height="Auto" />
        </Grid.RowDefinitions>

        <TextBlock Text="{Binding Message}" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Grid.Row="0" TextWrapping="Wrap" />
        <Button Command="{Binding CloseDialogCommand}" CommandParameter="true" Content="OK" Width="75" Height="25" HorizontalAlignment="Right" Margin="0,10,0,0" Grid.Row="1" IsDefault="True" />
    </Grid>
</UserControl>