KeyDown、KeyUp 和 KeyPressed 不会在托管 WPF 控件的 WinForms 应用程序上触发

Question

I've made a test WinForms APP in C# targeting .NET 4.5. The App uses System.Windows.Controls.Canvas to draw a white rectangle on a black background.

I've troubles with the keyboard-related events.

Full source is the following

using System;
using System.Drawing;
using System.Windows.Controls;
using System.Windows.Forms;
using System.Windows.Forms.Integration;
using Brushes = System.Windows.Media.Brushes;
using Panel = System.Windows.Forms.Panel;
using Rectangle = System.Windows.Shapes.Rectangle;
using UserControl = System.Windows.Controls.UserControl;

namespace WpfHostApp
{
    internal static class Program
    {
        /// <summary>
        /// Entry point.
        /// </summary>
        [STAThread]
        private static void Main()
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);

            var panel = new Panel { Dock = DockStyle.Fill };

            var form = new Form {Size = new Size(800, 600), Text = "WPF Host Form"};
            form.Controls.Add(panel);

            var rectangle = new Rectangle {Fill = Brushes.White, Width = 100, Height = 100};

            var canvas = new Canvas {Background = Brushes.Black};
            canvas.Children.Add(rectangle);

            var userControl = new UserControl {Content = canvas};

            var elementHost = new ElementHost {Child = userControl, Dock = DockStyle.Fill};

            panel.Controls.Add(elementHost);

            form.KeyDown += (sender, args) => MessageBox.Show("Key pressed!");

            Application.Run(form);
        }
    }
}

The form.KeyDown event won't fire (practically form.Key* won't fire), but if I comment the line panel.Controls.Add(elementHost); the event fires but obviously no canvas is drawn.

I can't see what in the example code above could cause this issue. What could be the culprit?

EDIT:

I've added a recursive function for suscribing KeyDown... no results

In Main() , after form.KeyDown :

foreach (Control control in form.Controls)
{
    SuscribeKeyDown(control);
}

SuscribeKeyDown(Control control) function:

private static void SuscribeKeyDown(Control control)
{
    control.KeyDown += (sender, args) => MessageBox.Show("Key pressed!");
    foreach (Control controlNested in control.Controls)
    {
        SuscribeKeyDown(controlNested);
    }
}

Answer 1

Set canvas.Focusable to true and catch the KeyDown event of the canvas:

[STAThread]
private static void Main()
{
    Application.EnableVisualStyles();
    Application.SetCompatibleTextRenderingDefault(false);

    var panel = new System.Windows.Forms.Panel { Dock = DockStyle.Fill };

    var form = new Form { Size = new Size(800, 600), Text = "WPF Host Form" };
    form.Controls.Add(panel);

    var rectangle = new System.Windows.Shapes.Rectangle { Fill = System.Windows.Media.Brushes.White, Width = 100, Height = 100 };

    var canvas = new Canvas { Background = System.Windows.Media.Brushes.Black,
        Focusable = true};
    canvas.Children.Add(rectangle);

    var userControl = new System.Windows.Controls.UserControl { Content = canvas };

    var elementHost = new ElementHost { Child = userControl, Dock = DockStyle.Fill };

    panel.Controls.Add(elementHost);

    // form.KeyDown += (sender, args) => MessageBox.Show("Key pressed!");
    canvas.KeyDown += (sender, args) => MessageBox.Show("Key pressed!");

    Application.Run(form);
}

Answer 2

Make sure the control is selected and has the focus

MyWinformChild.Select();
if(MyWinformChild.Focus())

Hook on LostFocus to keep it selected or simply to know when it happens

MyWinformChild.LostFocus += MyWinformChild_LostFocus;

Answer 3

You should set the form's KeyPreview field to true . Then your form's KeyDown event will work.

Answer 4

Add to Form TabControl and put ElementHost to TabPage. And now KeyDown/KeyUp will be work. Not the best practice, but it works.