NHotkey

Easily handle shortcut keys even when your WPF or WinForms app doesn't have focus. Declare hotkeys in XAML with the familiar KeyBinding syntax.

Nuget packages:

for WPF: NHotkey.Wpf
for Windows Forms: NHotkey.WindowsForms

Windows Forms usage

Add a reference to NHotkey.dll and NHotkey.WindowsForms.dll. In the file where you want to handle hotkeys, import the NHotkey.WindowsForms namespace:

    using NHotkey.WindowsForms;

During initialization, add some hotkeys:

    HotkeyManager.Current.AddOrReplace("Increment", Keys.Control | Keys.Alt | Keys.Add, OnIncrement);
    HotkeyManager.Current.AddOrReplace("Decrement", Keys.Control | Keys.Alt | Keys.Subtract, OnDecrement);

the first parameter is an application-defined name for the hotkey; it can be anything you like, as long as it's unique;
the second parameter is the combination of keys for which you want to register a hotkey;
the last parameter is a delegate of type EventHandler<HotkeyEventArgs> that will be called when this hotkey is pressed. For instance:

    private void OnIncrement(object sender, HotkeyEventArgs e)
    {
        Value++;
        e.Handled = true;
    }

    private void OnDecrement(object sender, HotkeyEventArgs e)
    {
        Value--;
        e.Handled = true;
    }

If you want to handle several hotkeys with the same handler, you can check the Name property of the HotkeyEventArgs:

    private void OnIncrementOrDecrement(object sender, HotkeyEventArgs e)
    {
        switch (e.Name)
        {
            case "Increment":
                Value++;
                break;
            case "Decrement":
                Value--;
                break;
        }
        e.Handled = true;
    }

WPF usage

The approach for WPF is very similar to the one for Windows Forms; the exposed API is slightly different to account for the differences between WinForms and WPF. The WPF version also supports KeyBindings.

Add a reference to NHotkey.dll and NHotkey.Wpf.dll. In the file where you want to handle hotkeys, import the NHotkey.Wpf namespace:

    using NHotkey.Wpf;

During initialization, add some hotkeys:

    HotkeyManager.Current.AddOrReplace("Increment", Key.Add, ModifierKeys.Control | ModifierKeys.Alt, OnIncrement);
    HotkeyManager.Current.AddOrReplace("Decrement", Key.Subtract, ModifierKeys.Control | ModifierKeys.Alt, OnDecrement);

the first parameter is an application-defined name for the hotkey; it can be anything you like, as long as it's unique;
the second and third parameters are the key and modifiers for which you want to register a hotkey;
the last parameter is a delegate of type EventHandler<HotkeyEventArgs> that will be called when this hotkey is pressed.

To support applications that use the MVVM pattern, you can also specify hotkeys in XAML using InputBindings. Just declare KeyBindings as usual, and set the HotkeyManager.RegisterGlobalHotkey attached property to true:

    ...
    <Window.InputBindings>
        <KeyBinding Gesture="Ctrl+Alt+Add" Command="{Binding IncrementCommand}"
                    HotkeyManager.RegisterGlobalHotkey="True" />
        <KeyBinding Gesture="Ctrl+Alt+Subtract" Command="{Binding DecrementCommand}"
                    HotkeyManager.RegisterGlobalHotkey="True" />
    </Window.InputBindings>
    ...

Known limitations of this feature

the HotkeyManager can't detect if you remove a KeyBinding; it only relies on the attached property being set to true or false. If you want to remove a KeyBinding at runtime, make sure you set HotkeyManager.RegisterGlobalHotkey to false, otherwise it will still be registered
changing the keys or modifiers of a KeyBinding at runtime is currently not supported. If you need to modify a KeyBinding at runtime, you need to set HotkeyManager.RegisterGlobalHotkey to false, change the key, and set HotkeyManager.RegisterGlobalHotkey to true again.

thomaslevesque/NHotkey

NHotkey

Windows Forms usage

WPF usage