Win8 Metro で MultiByteToWideChar を使う

TextDecoder.cs

public class TextDecoder
{
    [DllImport("Kernel32.dll", CharSet = CharSet.Unicode)]
    static extern int MultiByteToWideChar(
                        uint CodePage, 
                        uint dwFlags,
                        [MarshalAs(UnmanagedType.LPArray)] byte[] lpMultiByteStr, 
                        int cbMultiByte,
                        [Out, MarshalAs(UnmanagedType.LPWStr)] StringBuilder lpWideCharStr, 
                        int cchWideChar);

    public static string ReadAsShiftJis(byte[] bArray)
    {
        const uint CP_OEMCP = 1U;

        StringBuilder translatedString = new StringBuilder(bArray.Length + 1);
        MultiByteToWideChar(CP_OEMCP, 0, bArray, -1,
            translatedString, translatedString.Capacity);
        // WP8 では、実行時に↑ココで例外。

        return translatedString.ToString();
    }
}