How do I detect keyPress while not focused?
Well, if you had problems with System hooks, here is ready-made solution (based on http://www.dreamincode.net/forums/topic/180436-global-hotkeys/):
Define static class in your project:
public static class Constants
{
//windows message id for hotkey
public const int WM_HOTKEY_MSG_ID = 0x0312;
}
Define class in your project:
public class KeyHandler
{
[DllImport("user32.dll")]
private static extern bool RegisterHotKey(IntPtr hWnd, int id, int fsModifiers, int vk);
[DllImport("user32.dll")]
private static extern bool UnregisterHotKey(IntPtr hWnd, int id);
private int key;
private IntPtr hWnd;
private int id;
public KeyHandler(Keys key, Form form)
{
this.key = (int)key;
this.hWnd = form.Handle;
id = this.GetHashCode();
}
public override int GetHashCode()
{
return key ^ hWnd.ToInt32();
}
public bool Register()
{
return RegisterHotKey(hWnd, id, 0, key);
}
public bool Unregiser()
{
return UnregisterHotKey(hWnd, id);
}
}
add usings:
using System.Windows.Forms;
using System.Runtime.InteropServices;
now, in your Form, add field:
private KeyHandler ghk;
and in Form constructor:
ghk = new KeyHandler(Keys.PrintScreen, this);
ghk.Register();
Add those 2 methods to your form:
private void HandleHotkey()
{
// Do stuff...
}
protected override void WndProc(ref Message m)
{
if (m.Msg == Constants.WM_HOTKEY_MSG_ID)
HandleHotkey();
base.WndProc(ref m);
}
HandleHotkey is your button press handler. You can change the button by passing different parameter here: ghk = new KeyHandler(Keys.PrintScreen, this);
Now your program reacts for buton input even if not focused.
The API GetAsyncKeyState()
may be a perfectly acceptable alternative to setting up Windows Hook.
This depends on how you desire to receive the input. If you prefer event-driven notifications, then a hook is the way to go; however, if you prefer polling the keyboard for state changes, you can use the API above.
Here is a simple demonstration of how to use GetAsyncKeyState
:
Derived from Pinvoke.NET
[DllImport("User32.dll")]
private static extern short GetAsyncKeyState(int vKey);
private static readonly int VK_SNAPSHOT = 0x2C; //This is the print-screen key.
//Assume the timer is setup with Interval = 16 (corresponds to ~60FPS).
private System.Windows.Forms.Timer timer1 = new System.Windows.Forms.Timer();
private void timer1_Tick(object sender, EventArgs e)
{
short keyState = GetAsyncKeyState(VK_SNAPSHOT);
//Check if the MSB is set. If so, then the key is pressed.
bool prntScrnIsPressed = ((keyState >> 15) & 0x0001) == 0x0001;
//Check if the LSB is set. If so, then the key was pressed since
//the last call to GetAsyncKeyState
bool unprocessedPress = ((keyState >> 0) & 0x0001) == 0x0001;
if (prntScrnIsPressed)
{
//TODO Execute client code...
}
if (unprocessedPress)
{
//TODO Execute client code...
}
}
Yes you can, it's called "System hooks", take a look at Global System Hooks in .NET.