更改代码以.NET 2.0

Question

这似乎是.NET 2.0不支持字典键OrderByDescending，我怎样才能改变这种代码到.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

此行

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

只是得到最长的字节数组的长度在你的字典的键。因此，只需遍历imageFormatDecoders中的项目并记录最长的值，即如下所示（未经测试）：

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

Answer 2

你是什么意思的是.NET 3.5不支持OrderByDescending。它的确如此。顺便说一下Max(x => x.Length)有什么问题？

Answer 3

有什么不对的，在.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); 
} 

输出

Answer 4

我怀疑你只是缺乏;

using System.Linq; 

在代码文件的顶部。不，切换到.net 2在这里不会有帮助。