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In .NETCF v3.5 there is a new namespace – System.Media which brings audio support to the Compact Framework. Previously the common way to add sounds to your application was to use the PlaySound API (either P/Invoking yourself or using one of many wrappers). Now that the framework itself has built-in support, which matches the desktop .NET v2.0 framework it makes sense to standardise on the SoundPlayer component.

There are some differences in behaviour which you’ll need to be aware of. When you specify a filename this doesn’t simply call through to the native APIs passing the filename, the file is first loaded into memory and then the WaveOut APIs are used to play it. This means that if you simply create a new SoundPlayer and call Play the file will not be loaded, the Play method will have to first load the file contents, and then play the sound. This will create a noticable delay before the sound is heard. The class allows you to load the file at any time prior to calling play – you can use either Load or LoadAsync to do this. Once the file is loaded the Play method will be able to immediately begin playing the file. Exactly where you call the Load/LoadAsync method will depend on your application design. Keeping a large audio file cached will tie up valuable memory, you should dispose of the SoundPlayer instance once you have finished with it.

On the newsgroup somebody asked how to have multiple lines of text on a .NETCF Button control. The native control supports this but the appropriate style is not set by default. The following code snippet shows how to enable this:-

private const int BS_MULTILINE = 0x00002000;
private const int GWL_STYLE = -16;

[System.Runtime.InteropServices.DllImport(“coredll”)]
private static extern int GetWindowLong(IntPtr hWnd, int nIndex);

[System.Runtime.InteropServices.DllImport(“coredll”)]
private static extern int SetWindowLong(IntPtr hWnd, int nIndex, int dwNewLong);

public static void MakeButtonMultiline(Button b)
{
    IntPtr hwnd = b.Handle;
    int currentStyle = GetWindowLong(hwnd, GWL_STYLE);
    int newStyle = SetWindowLong(hwnd, GWL_STYLE, currentStyle | BS_MULTILINE);
}

The usage is simple, just pass the specific Button control to MakeButtonMultiline:-