Question

我的想法是用字符串填充字典作为键，字符串作为值填充。其中x =生成在目录中的某个文件的base64EncodedString，y =这表示文件名以及扩展名，fileName.extension

我正在遍历本地目录中的一堆文件，并获取base64string以及每个文件的filename.extension。在这个过程中，我检查给定键的值是否已经存在，如果它确实存在，我不添加键值对，否则我填充字典。

以下是我的代码，我是初学者，我正在努力解决这个问题。

Dictionary<string, string> d = new Dictionary<string, string>();
string[] attachmentPaths = Directory.GetFiles("someLocalFilePathPopulatedWithFiles");
Byte[] attachmentBytes;
string base64EncodedString;
string attachmentFileName;

foreach (string attachment in attachmentPaths)
{
  //Base 64 conversion process
  attachmentBytes = File.ReadAllBytes(attachment);
  base64EncodedString = Convert.ToBase64String(attachmentBytes);
  attachmentFileName = Path.GetFileName(attachment);

  if (d.TryGetValue(base64EncodedString, out attachmentFileName))
  {
    Console.WriteLine("exists");
    //trying to get a value for a key that does not exist, on the first iteration, then the compiler jumps to the else{}
  }
  else
  {
    Console.WriteLine("!exists");
    //Since the <key, value> does not exist, go ahead and populate the dictionary
    d.Add(base64EncodedString, attachmentFileName);
  }
}

//Print out the key value pair.
//The value is not being printed.
foreach (KeyValuePair<string, string> pair in d)
{
  Console.WriteLine("Key: " + pair.Key + " " + "Value: " + pair.Value);
}

问题是该值未被打印。

我还尝试使用更简单的代码来测试逻辑，它似乎工作。这似乎工作，因为我能够用我想要的数据填充字典对象，并在过程中检查它是否已经存在。

Dictionary<string, string> d = new Dictionary<string, string>();
d.Add("B", "fileB");
d.Add("C", "fileC");
d.Add("D", "fileD");
////we have an empty dicitonary, so lets try to get the value of key that IS not part of dictionary
string val = "fileA";

if (d.TryGetValue("A", out val))
{
  Console.WriteLine("exists");
  //do not add a key, since the <key ,value> exists
  //so the compiler will always jump to the else, {adding a <key, value>}
}
else
{
 Console.WriteLine("!exists");
 d.Add("A", "fileA");
}
foreach (KeyValuePair<string, string> pair in d)
{
  Console.WriteLine("Key: " + pair.Key + " " + "Value: " + pair.Value);
}

我确信存在差异，但我似乎没有抓住它，因为我仍在努力学习。

Answer 1

d.TryGetValue（base64EncodedString，out attachmentFileName））。如果attachmentFileName不存在，该行将清除attachmentFileName，因此在您的else部分中，您只添加null。你需要在这里使用另一个变量来测试它是否存在。使用一些临时变量来检查是否存在

foreach (string attachment in attachmentPaths)
{
  //Base 64 conversion process
  attachmentBytes = File.ReadAllBytes(attachment);
  base64EncodedString = Convert.ToBase64String(attachmentBytes);
  attachmentFileName = Path.GetFileName(attachment);
  var filename=string.Empty;

  if (d.TryGetValue(base64EncodedString, out filename))
  {
    Console.WriteLine("exists");
    //trying to get a value for a key that does not exist, on the first iteration, then the compiler jumps to the else{}
  }
  else
  {
    Console.WriteLine("!exists");
    //Since the <key, value> does not exist, go ahead and populate the dictionary
    d.Add(base64EncodedString, attachmentFileName);
  }
}

//Print out the key value pair.
//The value is not being printed.
foreach (KeyValuePair<string, string> pair in d)
{
  Console.WriteLine("Key: " + pair.Key + " " + "Value: " + pair.Value);
}

Answer 2

编辑：在OP评论后完成重写。

如果重点是查找内容与其他文件内容重复的文件，那么@Thangadurai的回答应该足以让您立即解决问题。

我仍然建议您计算每个文件内容的摘要/哈希值，然后使用基本64位编码版本作为词典键。这样，在方法运行时，您不必将每个文件的全部内容存储在内存中。像这样的东西（只是非常快速地测试）：

Dictionary<string, string> d = new Dictionary<string, string>();
string[] attachmentPaths = Directory.GetFiles("c:\\temp");

System.Security.Cryptography.SHA1Managed sha1 = new System.Security.Cryptography.SHA1Managed();
byte[] oneFileHash = null;

foreach (string attachment in attachmentPaths)
{
    using (FileStream oneFileStream = File.OpenRead(attachment))
    {
        oneFileHash = sha1.ComputeHash(oneFileStream);
    }
    if (oneFileHash == null)
        continue;

    string base64EncodedHash = Convert.ToBase64String(oneFileHash);
    string attachmentFileName = Path.GetFileName(attachment);

    if (d.ContainsKey(base64EncodedHash))
    {
        Console.WriteLine("exists");
        //trying to get a value for a key that does not exist, on the first iteration, then the compiler jumps to the else{}
    }
    else
    {
        Console.WriteLine("!exists");
        //Since the <key, value> does not exist, go ahead and populate the dictionary
        d.Add(base64EncodedHash, attachmentFileName);
    }
}

foreach (KeyValuePair<string, string> pair in d)
{
    Console.WriteLine("Key: " + pair.Key + " " + "Value: " + pair.Value);
}

如果我是你，我不会浪费任何关于ContainsKey和TryGetValue的相对表现的想法。它们都不是这里的瓶颈。如果你想检查字典是否已包含某个键，请继续使用最清楚地表明它正在为你做这个的方法。

注意：理论上有两个具有不同内容的文件最终会使用相同的哈希值。这种情况发生的可能性很小。这么小，你可以在实践中完全忽略它......

当我在字符串[]上迭代以获取<key，value =“”>对时，值未填充到字典<string，string =“”>中

2 个答案: