Introduction
When I created an application which needed to be notified whenever a combination of keys is pressed, I noticed there is no standard solution provided for this usecase.
My goal was to write a library that allowed to define hotkeys and send notifications to the subscribed objects even when the application has no focus, is minimized, etc.
I simplified my library to demonstrate a possible approach.
Using the Code
The project is composed of two assemblies:
- Hotkeys.dll (class library)
- HotKeyTest.exe (WPF test project)
Hotkeys.dll
Eums.cs contains Keys and Modifiers enumerations as provided in System.Windows.Input.
WinAPI.cs contains two methods needed for our usecase:
RegisterHotKeyUnregisterHotKey
HotkeyListener.cs encapsulates the interaction with the WinAPI to provide a facade between the WinAPI and the code consuming the HotKeys library code.
HotKey.cs encapsulates the definition of a HotKey namely Modifiers (4bits) and Key. Each unique combination gets a unique ID, calculated as follows: cast both enums to integers, shift the Key number with 4 positions (modifiers are composed out of 4 bits) and add the resulting integers.
HotKeyEventArgs is a specialisation of EventArgs containing:
- definition of the pressed
hotkey - the time it was pressed
HotKeyTest.dll
Contains a simple WPF application for testing purposes.
Control + Shift + N is defined by default, by clicking the button, you can add Control + K as a shortcut.
Using the library is as simple as getting an instance of the HotKeyListener class through the singleton pattern + supply the hotkeys you are interested in.
HotKeyListener.getInstance()
.listenTo(HotKeys.ModifierKeys.Control | HotKeys.ModifierKeys.Shift, Keys.N, this.Hk_press);
Points of Interest
The HotKey class contains some code to ensure that the same handler can't subscribe twice for an event.
In the HotKeyListener class, I had to use ComponentDispatcher to have WPF play nicely with the WinAPI.
History
- 30/06/2016: Initial version
