Change Code to .net 2.0

Question

hi

It seem that .net 2.0 do not support OrderByDescending for dictionary keys , how can I change this code to .net 2.0

    private static Dictionary<byte[], Func<BinaryReader, Size>> imageFormatDecoders = new Dictionary<byte[], Func<BinaryReader, Size>>()
 {
     { new byte[]{ 0x42, 0x4D }, DecodeBitmap},
     { new byte[]{ 0x47, 0x49, 0x46, 0x38, 0x37, 0x61 }, DecodeGif },
     { new byte[]{ 0x47, 0x49, 0x46, 0x38, 0x39, 0x61 }, DecodeGif },
     { new byte[]{ 0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A }, DecodePng },
     { new byte[]{ 0xff, 0xd8 }, DecodeJfif },
 };


public static Size GetDimensions(BinaryReader binaryReader)
     {
         int maxMagicBytesLength = imageFormatDecoders.Keys.OrderByDescending(x => x.Length).First().Length;
         byte[] magicBytes = new byte[maxMagicBytesLength];
         for (int i = 0; i < maxMagicBytesLength; i += 1)
         {
             magicBytes[i] = binaryReader.ReadByte();
             foreach (var kvPair in imageFormatDecoders)
             {
                 if (magicBytes.StartsWith(kvPair.Key))
                 {
                     return kvPair.Value(binaryReader);
                 }
             }
         }
         throw new ArgumentException(errorMessage, "binaryReader");
     }

Answer 1

What do you mean that .net 3.5 does not support OrderByDescending. It does. And by the way what is wrong with Max(x => x.Length)?

Answer 2

What's wrong with this, in .Net 3.5?

Dictionary<int, int> dict = new Dictionary<int, int>();
dict[0] = 2;
dict[1] = 3;

foreach (var item in dict.OrderByDescending(key => key.Value))
{
    Console.WriteLine(item.Key);
    Console.WriteLine(item.Value);
} 

Output

1

3

0

2

Answer 3

I suspect you simply lack;

using System.Linq;

At the top of the code file. And no, switching to .net 2 won't help here.

Answer 4

This line

int maxMagicBytesLength = imageFormatDecoders.Keys.OrderByDescending(x => x.Length).First().Length;

just gets the length of the longest byte array in the keys of your dictionary. So just iterate through your items in imageFormatDecoders and record the longest value, i.e., something like this (untested):

int maxMagicBytesLength = 0;
foreach (byte[] magicBytes in imageFormatDecoders.Keys) {
    if (magicBytes.Length > maxMagicBytesLength)
        maxMagicBytesLength = magicBytes.Length;
}