Question

The WPF program below puts up a window which looks like this:

Mouse-movement outside the black square causes the window title to be updated with the mouse’s position. The updating stops when the mouse enters the square.

I’d like for MouseMove to continue to trigger even when the mouse is over the square. Is there a way to do this?

using System.Windows;
using System.Windows.Controls;
using System.Windows.Media;

namespace Wpf_Particle_Demo
{
    class DrawingVisualElement : FrameworkElement
    {
        public DrawingVisual visual;

        public DrawingVisualElement() { visual = new DrawingVisual(); }

        protected override int VisualChildrenCount { get { return 1; } }

        protected override Visual GetVisualChild(int index) { return visual; }
    }

    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();

            var canvas = new Canvas();

            Content = canvas;

            var element = new DrawingVisualElement();

            canvas.Children.Add(element);

            CompositionTarget.Rendering += (s, e) =>
                {
                    using (var dc = element.visual.RenderOpen())
                        dc.DrawRectangle(Brushes.Black, null, new Rect(0, 0, 50, 50));
                };

            MouseMove += (s, e) => Title = e.GetPosition(canvas).ToString();
        }
    }
}

Answer 1

You will need to Capture the mouse this will allow your Canvas to continue to respond to the MouseMove Event, Try something like this it will update your coordinates as long as the Mouse is Pressed

public partial class MainWindow : Window
{

    public MainWindow()
    {
        InitializeComponent();


        var canvas = new Canvas();
        Content = canvas;

        var element = new DrawingVisualElement();

        canvas.Children.Add(element);
        CompositionTarget.Rendering += (s, e) =>
        {
            using (var dc = element.visual.RenderOpen())
                dc.DrawRectangle(Brushes.Black, null, new Rect(0, 0, 50, 50));
        };

        Mouse.Capture(canvas);
        MouseDown += (s, e) => Mouse.Capture((UIElement)s);
        MouseMove += (s, e) => Title = e.GetPosition(canvas).ToString();
        MouseUp += (s, e) => Mouse.Capture(null);

    }

---

Second Method

public MainWindow()
{
    InitializeComponent();
    var canvas = new Canvas();
    Content = canvas;

    DrawingVisualElement element = new DrawingVisualElement();
    Grid myElement = new Grid();
    canvas.Children.Add(myElement);

    CompositionTarget.Rendering += (s, e) =>
    {
        using (var dc = element.visual.RenderOpen())
        {
            dc.DrawRectangle(Brushes.Black, null, new Rect(100, 0, 50, 50));
        }

        DrawingImage myImage = new DrawingImage(element.visual.Drawing);
        myElement.Height = myImage.Height;
        myElement.Width = myImage.Width;
        myElement.Background = new ImageBrush(myImage);
    };


    MouseMove += (s, e) => Title = e.GetPosition(canvas).ToString();
}

---

Using a Hook be sure to put a using System.Windows.Interop;

public partial class MainWindow : Window
{


    public MainWindow()
    {
        InitializeComponent();
        var canvas = new Canvas();
        Content = canvas;

        var element = new DrawingVisualElement();
        canvas.Children.Add(element);

        CompositionTarget.Rendering += (s, e) =>
        {
            using (var dc = element.visual.RenderOpen())
            {
                dc.DrawRectangle(Brushes.Black, null, new Rect(0, 0, 50, 50));
            }
        };
        this.SourceInitialized += new EventHandler(OnSourceInitialized);
    }

    void OnSourceInitialized(object sender, EventArgs e)
    {
        HwndSource source = (HwndSource)PresentationSource.FromVisual(this);
        source.AddHook(new HwndSourceHook(HandleMessages));

    }
    IntPtr HandleMessages(IntPtr hwnd, int msg,IntPtr wParam, IntPtr lParam, ref bool handled)
    {
        if (msg == 0x200)
            Title = Mouse.GetPosition(this).ToString(); // because I did not want to split the lParam into High/Low values for Position information
        return IntPtr.Zero;
    }
}