判断文件的类型

public static bool IsPicture(string filePath)
{
try
{

System.IO.FileStream fs = new System.IO.FileStream(filePath, System.IO.FileMode.Open, System.IO.FileAccess.Read);
System.IO.BinaryReader reader = new System.IO.BinaryReader(fs);
string fileClass;
byte buffer;
byte[] b = new byte[2];
buffer = reader.ReadByte();
b[0] = buffer;
fileClass = buffer.ToString();
buffer = reader.ReadByte();
b[1] = buffer;
fileClass += buffer.ToString();

reader.Close();
fs.Close();
if (fileClass == "255216" || fileClass == "7173" || fileClass == "6677" || fileClass == "13780")//255216是jpg;7173是gif;6677是BMP,13780是PNG;7790是exe,8297是rar
{
return true;
}
else
{
return false;
}
}
catch
{
return false;
}
}