c# - 为什么我收到 "Expression always true"警告？

Question

这是出现警告的代码:

public async Task<Metadata> GetFolderAsync(string strDirectoryPathName, dynamic varKnownFolder = null)
{
    using (await _FolderPathToInfoMapSync.EnterAsync().ConfigureAwait(false))
    {
        Metadata objFolder;
        string strPathName = strDirectoryPathName;
        if (varKnownFolder == null)
        {
            objFolder = await _Storage.Client.Files.GetMetadataAsync(strPathName);
        }
        else
        {
            //Here warning arises
            if (varKnownFolder != null) _FolderPathToInfoMap.Add(strDirectoryPathName, varKnownFolder);
            else objFolder = null;
        }
    }
    return objFolder;
}

我的意思是原因是方法签名中的 varKnownFolder，但我不明白这里出了什么问题。

Answer 1

如果您的代码进入第一个 else block ，则意味着 (varKnownFolder == null) 被评估为 false。

所以第二次检查是无用的，因为 varKnownFolder 在此 block 中永远不会为 null。

public async Task<Metadata> GetFolderAsync(string strDirectoryPathName, dynamic varKnownFolder = null)
{
     using (await _FolderPathToInfoMapSync.EnterAsync().ConfigureAwait(false))
     {
           Metadata objFolder;
           string strPathName = strDirectoryPathName;

           if (varKnownFolder == null)
           {
               // This would happen if varKnownFolder is null 

               objFolder = await _Storage.Client.Files.GetMetadataAsync(strPathName);
           }
           else
           {
               // The code enters HERE BECAUSE varKnownFolder is not null

               if (varKnownFolder != null) // <-- So this check is useless
                   _FolderPathToInfoMap.Add(strDirectoryPathName, varKnownFolder);
               else 
                  objFolder = null;
            }

            return objFolder;
      }

}

此外，这意味着您可以将其替换为:

public async Task<Metadata> GetFolderAsync(string strDirectoryPathName, dynamic varKnownFolder = null)
{
     using (await _FolderPathToInfoMapSync.EnterAsync().ConfigureAwait(false))
     {
           Metadata objFolder = null;
           string strPathName = strDirectoryPathName;

           if (varKnownFolder == null)
           {
               objFolder = await _Storage.Client.Files.GetMetadataAsync(strPathName);
           }
           else
           {
               // The code enters HERE BECAUSE varKnownFolder is not null
               _FolderPathToInfoMap.Add(strDirectoryPathName, varKnownFolder);
            }

            return objFolder;
      }

}