Compact Framework: Global Hotkeys
A long time ago, in a galaxy far far away… well… back when I worked in VB.NET up in Dallas… I wrote a little hot key class for compact framework apps and posted a little bit on how to use it. Of course that was all done in VB.NET and I haven’t used that since the end of 2005. Fast forward 5 years and I find myself using the Compact Framework a lot and needing hotkeys again. So, here is the same code translated into C# (with the help of PInvoke.NET):
1: using System;
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<pre><span style="color: #606060"> 2:</span> <span style="color: #0000ff">using</span> System.Windows.Forms;</pre>
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<pre><span style="color: #606060"> 3:</span> <span style="color: #0000ff">using</span> Microsoft.WindowsCE.Forms;</pre>
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<pre><span style="color: #606060"> 4:</span> <span style="color: #0000ff">using</span> System.Runtime.InteropServices;</pre>
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<pre><span style="color: #606060"> 5:</span>  </pre>
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<pre><span style="color: #606060"> 6:</span> <span style="color: #0000ff">namespace</span> CFHotKeys</pre>
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<pre><span style="color: #606060"> 7:</span> {</pre>
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<pre><span style="color: #606060"> 8:</span> <span style="color: #0000ff">public</span> <span style="color: #0000ff">class</span> HotKeys</pre>
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<pre><span style="color: #606060"> 9:</span> {</pre>
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<pre><span style="color: #606060"> 10:</span> <span style="color: #cc6633">#region</span> dll imports</pre>
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<pre><span style="color: #606060"> 11:</span>  </pre>
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<pre><span style="color: #606060"> 12:</span> [DllImport(<span style="color: #006080">"coredll.dll"</span>)]</pre>
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<pre><span style="color: #606060"> 13:</span> <span style="color: #0000ff">private</span> <span style="color: #0000ff">static</span> <span style="color: #0000ff">extern</span> <span style="color: #0000ff">bool</span> RegisterHotKey(IntPtr hWnd, <span style="color: #0000ff">int</span> id, <span style="color: #0000ff">int</span> fsModifiers, <span style="color: #0000ff">int</span> vlc);</pre>
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<pre><span style="color: #606060"> 14:</span>  </pre>
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<pre><span style="color: #606060"> 15:</span> [DllImport(<span style="color: #006080">"coredll.dll"</span>)]</pre>
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<pre><span style="color: #606060"> 16:</span> <span style="color: #0000ff">private</span> <span style="color: #0000ff">static</span> <span style="color: #0000ff">extern</span> <span style="color: #0000ff">bool</span> UnregisterHotKey(IntPtr hWnd, <span style="color: #0000ff">int</span> id);</pre>
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<pre><span style="color: #606060"> 17:</span>  </pre>
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<pre><span style="color: #606060"> 18:</span> <span style="color: #cc6633">#endregion</span></pre>
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<pre><span style="color: #606060"> 19:</span>  </pre>
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<pre><span style="color: #606060"> 20:</span> <span style="color: #0000ff">public</span> <span style="color: #0000ff">enum</span> KeyModifiers </pre>
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<pre><span style="color: #606060"> 21:</span> {</pre>
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<pre><span style="color: #606060"> 22:</span> None = 0,</pre>
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<pre><span style="color: #606060"> 23:</span> Alt = 1,</pre>
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<pre><span style="color: #606060"> 24:</span> Control = 2,</pre>
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<pre><span style="color: #606060"> 25:</span> Shift = 4,</pre>
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<pre><span style="color: #606060"> 26:</span> Windows = 8,</pre>
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<pre><span style="color: #606060"> 27:</span> Modkeyup = 0x1000</pre>
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<pre><span style="color: #606060"> 28:</span> }</pre>
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<pre><span style="color: #606060"> 29:</span>  </pre>
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<pre><span style="color: #606060"> 30:</span> <span style="color: #0000ff">public</span> <span style="color: #0000ff">delegate</span> <span style="color: #0000ff">void</span> KeyPressedEventHandler(Keys key);</pre>
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<pre><span style="color: #606060"> 31:</span>  </pre>
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<pre><span style="color: #606060"> 32:</span> <span style="color: #0000ff">public</span> <span style="color: #0000ff">event</span> KeyPressedEventHandler KeyPressed;</pre>
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<pre><span style="color: #606060"> 33:</span> <span style="color: #0000ff">private</span> <span style="color: #0000ff">readonly</span> HotKeyMessageWindow wnd;</pre>
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<pre><span style="color: #606060"> 34:</span>  </pre>
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<pre><span style="color: #606060"> 35:</span> <span style="color: #0000ff">public</span> HotKeys()</pre>
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<pre><span style="color: #606060"> 36:</span> {</pre>
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<pre><span style="color: #606060"> 37:</span> wnd = <span style="color: #0000ff">new</span> HotKeyMessageWindow(<span style="color: #0000ff">this</span>);</pre>
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<pre><span style="color: #606060"> 38:</span> }</pre>
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<pre><span style="color: #606060"> 39:</span>  </pre>
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<pre><span style="color: #606060"> 40:</span> <span style="color: #0000ff">public</span> <span style="color: #0000ff">void</span> Register(Keys Key)</pre>
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<pre><span style="color: #606060"> 41:</span> {</pre>
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<pre><span style="color: #606060"> 42:</span> RegisterHotKey(wnd.Hwnd, (<span style="color: #0000ff">int</span>)Key, 0, (<span style="color: #0000ff">int</span>)Key);</pre>
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<pre><span style="color: #606060"> 43:</span> }</pre>
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<pre><span style="color: #606060"> 44:</span>  </pre>
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<pre><span style="color: #606060"> 45:</span> <span style="color: #0000ff">public</span> <span style="color: #0000ff">void</span> Register(Keys Key, KeyModifiers Modifier)</pre>
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<pre><span style="color: #606060"> 46:</span> {</pre>
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<pre><span style="color: #606060"> 47:</span> RegisterHotKey(wnd.Hwnd, (<span style="color: #0000ff">int</span>)Key, (<span style="color: #0000ff">int</span>)Modifier, (<span style="color: #0000ff">int</span>)Key);</pre>
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<pre><span style="color: #606060"> 48:</span> }</pre>
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<pre><span style="color: #606060"> 49:</span>  </pre>
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<pre><span style="color: #606060"> 50:</span> <span style="color: #0000ff">public</span> <span style="color: #0000ff">void</span> UnRegister(Keys Key)</pre>
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<pre><span style="color: #606060"> 51:</span> {</pre>
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<pre><span style="color: #606060"> 52:</span> UnregisterHotKey(wnd.Hwnd, (<span style="color: #0000ff">int</span>)Key);</pre>
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<pre><span style="color: #606060"> 53:</span> }</pre>
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<pre><span style="color: #606060"> 54:</span>  </pre>
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<pre><span style="color: #606060"> 55:</span> <span style="color: #0000ff">public</span> <span style="color: #0000ff">void</span> OnKeyPressed(Keys key)</pre>
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<pre><span style="color: #606060"> 56:</span> {</pre>
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<pre><span style="color: #606060"> 57:</span> <span style="color: #008000">//forward the keypress event to the outside world.</span></pre>
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<pre><span style="color: #606060"> 58:</span>  </pre>
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<pre><span style="color: #606060"> 59:</span> <span style="color: #0000ff">if</span> (KeyPressed != <span style="color: #0000ff">null</span>)</pre>
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<pre><span style="color: #606060"> 60:</span> {</pre>
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<pre><span style="color: #606060"> 61:</span> KeyPressed(key);</pre>
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<pre><span style="color: #606060"> 62:</span> }</pre>
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<pre><span style="color: #606060"> 63:</span> }</pre>
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<pre><span style="color: #606060"> 64:</span>  </pre>
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<pre><span style="color: #606060"> 65:</span> <span style="color: #0000ff">private</span> <span style="color: #0000ff">class</span> HotKeyMessageWindow : MessageWindow</pre>
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<pre><span style="color: #606060"> 66:</span> {</pre>
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<pre><span style="color: #606060"> 67:</span> <span style="color: #0000ff">private</span> <span style="color: #0000ff">const</span> <span style="color: #0000ff">int</span> WM_HOTKEY = 0x312;</pre>
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<pre><span style="color: #606060"> 68:</span> <span style="color: #0000ff">private</span> <span style="color: #0000ff">readonly</span> HotKeys parent;</pre>
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<pre><span style="color: #606060"> 69:</span>  </pre>
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<pre><span style="color: #606060"> 70:</span> <span style="color: #0000ff">public</span> HotKeyMessageWindow(HotKeys h)</pre>
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<pre><span style="color: #606060"> 71:</span> {</pre>
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<pre><span style="color: #606060"> 72:</span> parent = h;</pre>
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<pre><span style="color: #606060"> 73:</span> }</pre>
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<pre><span style="color: #606060"> 74:</span>  </pre>
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<pre><span style="color: #606060"> 75:</span> <span style="color: #0000ff">protected</span> <span style="color: #0000ff">override</span> <span style="color: #0000ff">void</span> WndProc(<span style="color: #0000ff">ref</span> Message msg)</pre>
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<pre><span style="color: #606060"> 76:</span> {</pre>
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<pre><span style="color: #606060"> 77:</span> <span style="color: #0000ff">switch</span> (msg.Msg)</pre>
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<pre><span style="color: #606060"> 78:</span> {</pre>
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<pre><span style="color: #606060"> 79:</span> <span style="color: #0000ff">case</span> WM_HOTKEY:</pre>
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<pre><span style="color: #606060"> 80:</span> {</pre>
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<pre><span style="color: #606060"> 81:</span> <span style="color: #0000ff">int</span> keyNum = msg.WParam.ToInt32();</pre>
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<pre><span style="color: #606060"> 82:</span> Keys key = (Keys) keyNum;</pre>
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<pre><span style="color: #606060"> 83:</span> parent.OnKeyPressed(key);</pre>
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<pre><span style="color: #606060"> 84:</span> <span style="color: #0000ff">break</span>;</pre>
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<pre><span style="color: #606060"> 85:</span> }</pre>
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<pre><span style="color: #606060"> 86:</span> <span style="color: #0000ff">default</span>:</pre>
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<pre><span style="color: #606060"> 87:</span> {</pre>
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<pre><span style="color: #606060"> 88:</span> <span style="color: #0000ff">base</span>.WndProc(<span style="color: #0000ff">ref</span> msg);</pre>
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<pre><span style="color: #606060"> 89:</span> <span style="color: #0000ff">break</span>;</pre>
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<pre><span style="color: #606060"> 90:</span> }</pre>
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<pre><span style="color: #606060"> 91:</span> }</pre>
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<pre><span style="color: #606060"> 92:</span> }</pre>
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<pre><span style="color: #606060"> 93:</span> }</pre>
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<pre><span style="color: #606060"> 94:</span> }</pre>
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<pre><span style="color: #606060"> 95:</span> }</pre>
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You’ll need to add a reference to Microsoft.WindowCE.Forms in your compact framework app.
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The hot key interop call technically requires a windows form to receive the hotkey press using a windows message pump handler. This isn’t available in the standard System.Windows.Forms, but it is available in the MessageWindow class in the Microsoft.WindowsCE.Forms assembly. This code instantiates a class that inherits from MessageWindow so that we can handle the hot key press from anywhere in our application, not just from a specific form.
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As an example of this being a global hotkey, create a Compact Framework app with a single form in it, and change your Program.cs to look like this:
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<pre><span style="color: #606060"> 1:</span> <span style="color: #0000ff">static</span> <span style="color: #0000ff">class</span> Program</pre>
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<pre><span style="color: #606060"> 2:</span> {</pre>
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<pre><span style="color: #606060"> 3:</span>  </pre>
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<pre><span style="color: #606060"> 4:</span> <span style="color: #0000ff">private</span> <span style="color: #0000ff">static</span> HotKeys hotKeys;</pre>
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<pre><span style="color: #606060"> 5:</span>  </pre>
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<pre><span style="color: #606060"> 6:</span> [MTAThread]</pre>
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<pre><span style="color: #606060"> 7:</span> <span style="color: #0000ff">static</span> <span style="color: #0000ff">void</span> Main()</pre>
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<pre><span style="color: #606060"> 8:</span> {</pre>
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<pre><span style="color: #606060"> 9:</span> hotKeys = <span style="color: #0000ff">new</span> HotKeys();</pre>
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<pre><span style="color: #606060"> 10:</span> hotKeys.Register(Keys.A);</pre>
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<pre><span style="color: #606060"> 11:</span> hotKeys.KeyPressed += hotKeys_KeyPressed;</pre>
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<pre><span style="color: #606060"> 12:</span>  </pre>
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<pre><span style="color: #606060"> 13:</span> Application.Run(<span style="color: #0000ff">new</span> Form1());</pre>
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<pre><span style="color: #606060"> 14:</span> }</pre>
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<pre><span style="color: #606060"> 15:</span>  </pre>
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<pre><span style="color: #606060"> 16:</span> <span style="color: #0000ff">private</span> <span style="color: #0000ff">static</span> <span style="color: #0000ff">void</span> hotKeys_KeyPressed(Keys key)</pre>
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<pre><span style="color: #606060"> 17:</span> {</pre>
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<pre><span style="color: #606060"> 18:</span> <span style="color: #0000ff">switch</span> (key)</pre>
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<pre><span style="color: #606060"> 19:</span> {</pre>
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<pre><span style="color: #606060"> 20:</span> <span style="color: #0000ff">case</span> Keys.A:</pre>
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<pre><span style="color: #606060"> 21:</span> {</pre>
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<pre><span style="color: #606060"> 22:</span> MessageBox.Show(<span style="color: #006080">"You pressed A!"</span>);</pre>
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<pre><span style="color: #606060"> 23:</span> <span style="color: #0000ff">break</span>;</pre>
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<pre><span style="color: #606060"> 24:</span> }</pre>
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<pre><span style="color: #606060"> 25:</span> <span style="color: #0000ff">default</span>: <span style="color: #0000ff">break</span>;</pre>
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<pre><span style="color: #606060"> 26:</span> }</pre>
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<pre><span style="color: #606060"> 27:</span> }</pre>
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<pre><span style="color: #606060"> 28:</span>  </pre>
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<pre><span style="color: #606060"> 29:</span> }</pre>
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<p>
Anytime you press the “a” or “A” key in the application, you’ll get a message box that pops up. The API for the HotKeys class could be made quite a bit more elegant, IMO. I don’t really like using switch statements like I showed in the program.cs… I would rather register a hotkey with a delegate that gets fired, like this:
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<pre><span style="color: #606060"> 1:</span> <span style="color: #0000ff">private</span> <span style="color: #0000ff">void</span> RegisterHotKeys()</pre>
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<pre><span style="color: #606060"> 2:</span> {</pre>
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<pre><span style="color: #606060"> 3:</span> hotKeys.Register(Keys.A, HandleAPress);</pre>
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<pre><span style="color: #606060"> 4:</span> }</pre>
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<pre><span style="color: #606060"> 5:</span>  </pre>
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<pre><span style="color: #606060"> 6:</span> <span style="color: #0000ff">private</span> <span style="color: #0000ff">void</span> HandleAPress()</pre>
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<pre><span style="color: #606060"> 7:</span> {</pre>
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<pre><span style="color: #606060"> 8:</span> MessageBox.Show(<span style="color: #006080">"You Presed A!"</span>);</pre>
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<pre><span style="color: #606060"> 9:</span> }</pre>
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<p>
I don’t want to spoil all the fun of playing with this little snippet of code, though. So I’ll let you, the reader, explore the possibilities of implementing this API. 🙂
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