How do i capture the Print Screen key?

Question

Hello everyone.

I my program i need to capture when the Print Screen key is pressed down but it is not working (however it works with other keys).

I guess this has something to do with windows hijacking my authority and since im still new at this i'd love to know how i can get around this issue.

Here's my current code:

namespace Boom_Screenshot_
{
/// <summary>
/// Interaction logic for Window1.xaml
/// </summary>
public partial class Window1 : Window
{
    //SETTINGS
    Key TRIGGER_KEY = Key.PrintScreen;


    public Window1()
    {
        InitializeComponent();
    }



    private void Window_KeyDown(object sender, KeyEventArgs e)
    {
        if (e.Key == TRIGGER_KEY)
        {
            MessageBox.Show("'PrintScreen' was pressed.");
        }
    }




}

}

Answer 1

I have an answer for you that I found here (I don't speak Chinese so don't ask me what it says :). You have to set a hook. He provides a wrapper class. I repeat some code here without the Chinese characters. RegisterHotKey.cs ...

using System;
using System.Runtime.InteropServices;
using System.Windows.Forms;

namespace TestKeydown
{
    public class RegisterHotKeyClass
    {
        private IntPtr m_WindowHandle = IntPtr.Zero;
        private MODKEY m_ModKey = MODKEY.MOD_CONTROL;
        private Keys m_Keys = Keys.A;
        private int m_WParam = 10000;
        private bool Star = false;
        private HotKeyWndProc m_HotKeyWnd = new HotKeyWndProc();

        public IntPtr WindowHandle
        {
            get { return m_WindowHandle; }
            set { if (Star)return; m_WindowHandle = value; }
        }
        public MODKEY ModKey
        {
            get { return m_ModKey; }
            set { if (Star)return; m_ModKey = value; }
        }
        public Keys Keys
        {
            get { return m_Keys; }
            set { if (Star)return; m_Keys = value; }
        }
        public int WParam
        {
            get { return m_WParam; }
            set { if (Star)return; m_WParam = value; }
        }

        public void StarHotKey()
        {
            if (m_WindowHandle != IntPtr.Zero)
            {
                if (!RegisterHotKey(m_WindowHandle, m_WParam, m_ModKey, m_Keys))
                {
                    throw new Exception("");
                }
                try
                {
                    m_HotKeyWnd.m_HotKeyPass = new HotKeyPass(KeyPass);
                    m_HotKeyWnd.m_WParam = m_WParam;
                    m_HotKeyWnd.AssignHandle(m_WindowHandle);
                    Star = true;
                }
                catch
                {
                    StopHotKey();
                }
            }
        }
        private void KeyPass()
        {
            if (HotKey != null) HotKey();
        }
        public void StopHotKey()
        {
            if (Star)
            {
                if (!UnregisterHotKey(m_WindowHandle, m_WParam))
                {
                    throw new Exception("");
                }
                Star = false;
                m_HotKeyWnd.ReleaseHandle();
            }
        }


        public delegate void HotKeyPass();
        public event HotKeyPass HotKey;


        private class HotKeyWndProc : NativeWindow
        {
            public int m_WParam = 10000;
            public HotKeyPass m_HotKeyPass;
            protected override void WndProc(ref Message m)
            {
                if (m.Msg == 0x0312 && m.WParam.ToInt32() == m_WParam)
                {
                    if (m_HotKeyPass != null) m_HotKeyPass.Invoke();
                }

                base.WndProc(ref m);
            }
        }

        public enum MODKEY
        {
            MOD_ALT = 0x0001,
            MOD_CONTROL = 0x0002,
            MOD_SHIFT = 0x0004,
            MOD_WIN = 0x0008,
        }

        [DllImport("user32.dll")]
        public static extern bool RegisterHotKey(IntPtr wnd, int id, MODKEY mode, Keys vk);

        [DllImport("user32.dll")]
        public static extern bool UnregisterHotKey(IntPtr wnd, int id);
    }
}

Calling code in a Form ...

private RegisterHotKeyClass _RegisKey = new RegisterHotKeyClass();

void _Regis_HotKey()
{
  MessageBox.Show("ok");
} 

private void Form1_Load(object sender, EventArgs e)
{
  _RegisKey.Keys = Keys.PrintScreen;
  _RegisKey.ModKey = 0;
  _RegisKey.WindowHandle = this.Handle;
  _RegisKey.HotKey += new RegisterHotKeyClass.HotKeyPass(_Regis_HotKey);
  _RegisKey.StarHotKey();
}

Answer 2

Below is my pure WPF solution.

We can achieve this in xaml by using NavigationCommands (Namespace: System.Window.Input) class which provides a standard set of navigation commands (e.g. NextPage, PreviousPage, Refresh, Search etc.)

Implementation Approach:

So we can call any custom code to execute on application refresh using NavigationCommands.Refresh as

<UserControl.CommandBindings>
<CommandBinding Command='NavigationCommands.Refresh'
                   Executed="ApplicationRefresh_Executed">
</CommandBinding>
</UserControl.CommandBindings>

Now in code behind class of UserControl we can define method as

private void ApplicationRefresh_Executed(object sender, ExecutedRoutedEventArgs e)
{
             // Implementation goes here.
}