Question

.net 2.0似乎不支持字典键的OrderByDescending，如何将此代码更改为.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

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对此没有帮助。

Answer 2

你是什么意思.net 3.5不支持OrderByDescending。确实如此。顺便说一下Max(x => x.Length)出了什么问题？

Answer 3

在.Net 3.5中出现了什么问题？

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

1

3

0

2

Answer 4

这一行

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

只获取字典中键中最长字节数组的长度。所以只需遍历imageFormatDecoders中的项目并记录最长的值，即类似的内容（未经测试）：

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

将代码更改为.net 2.0

4 个答案: