C#：如何在没有 "copy/paste" 代码的情况下重写它

Question

我有两个类似的方法：

    /// <summary>
    /// 
    /// </summary>
    /// <param name="domain"></param>
    /// <exception cref="DomainRecordNotFoundException">Throw when the dns record is not found in Office365</exception>
    /// <exception cref="DomainNotFoundException">Throw when domain is not added to Office365</exception>
    /// <exception cref="UnknownException">Unknown exception from Microsoft Graph</exception>
    /// <returns></returns>
    public async Task<string> GetMxRecordForDomainAsync(string domain)
    {
        try
        {
            var records = await _graphClient.Domains[domain].ServiceConfigurationRecords.Request().GetAsync();
            string mxRecord = String.Empty;

            foreach (var record in records)
            {
                if (record.RecordType == "Mx")
                {
                    mxRecord = ((Microsoft.Graph.DomainDnsMxRecord)record).MailExchange;
                    break;
                }
            }

            if (String.IsNullOrWhiteSpace(mxRecord))
                throw new DomainRecordNotFoundException(DomainRegistrationCore.Models.DomainRecordType.MX);

            return mxRecord;
        }
        catch (ServiceException graphEx)
        {
            if (graphEx.StatusCode == System.Net.HttpStatusCode.NotFound)
            {
                throw new DomainNotFoundException();
            }

            throw new UnknownException(graphEx.StatusCode, graphEx.Error.Message);
        }
    }

    /// <summary>
    /// 
    /// </summary>
    /// <param name="domain"></param>
    /// <exception cref="DomainRecordNotFoundException">Throw when the dns record is not found in Office365</exception>
    /// <exception cref="DomainNotFoundException">Throw when domain is not added to Office365</exception>
    /// <exception cref="UnknownException">Unknown exception from Microsoft Graph</exception>
    /// <returns></returns>
    public async Task<string> GetVerificationRecordForDomainAsync(string domain)
    {
        try
        {
            var records = (await _graphClient.Domains[domain].VerificationDnsRecords.Request().GetAsync());
            string verificationText = String.Empty;

            foreach (var record in records)
            {
                if (record.RecordType == "Txt")
                {
                    verificationText = ((Microsoft.Graph.DomainDnsTxtRecord)record).Text;
                    break;
                }
            }

            if (String.IsNullOrWhiteSpace(verificationText))
                throw new DomainRecordNotFoundException(DomainRegistrationCore.Models.DomainRecordType.TXT);

            return verificationText;
        }
        catch (ServiceException graphEx)
        {
            if (graphEx.StatusCode == System.Net.HttpStatusCode.NotFound)
            {
                throw new DomainNotFoundException();
            }

            throw new UnknownException(graphEx.StatusCode, graphEx.Error.Message);
        }
    }

正如我们所见，这两种方法只有这一部分不同：

        foreach (var record in records)
        {
            if (record.RecordType == **RECORD**)
            {
                mxRecord = ((**TYPE_OF_RECORD**)record).MailExchange;
                break;
            }
        }

        if (String.IsNullOrWhiteSpace(mxRecord))
            throw new DomainRecordNotFoundException(**RECORD**);

其他部分相同。我想为一种常用方法重写它，但不明白如何。我假设，我可以用 Func<> 或 Action<>

Answer 1

嗯，你可以先写下方法的简化模式并分析它们的结构：

Method1(domain)
  some stuff...
  foreach if(c1) res = (Type1)smth
  if (res == null) throw ex(errMsg1)

Method2(domain)
  some stuff...
  foreach if(c2) res = (Type2)smth
  if (res == null) throw ex(errMsg2)

那么每个功能都有什么？

常用代码（包括foreach循环）
'if' 语句中的某些特定条件
我们将结果转换为的特定类型
当结果为 null 或空时抛出的异常我们使用的特定错误消息

我们如何才能满足这些条件并创建一个功能？

对于我们列表中的第一名，我们不需要任何东西
对于第二个条件，我们可以传递参数，然后在 'if'条件。
对于第三种，我们可以使用泛型并将类型作为类型传递参数或转换结果为 dynamic
我们可以再次接受错误信息作为参数

因此，新方法的简化结构可能如下所示：

Method3<TDomainType>(domain, recordTypeToCheck, errorMsg)
  some stuff...
  foreach if(record.RecordType == recordTypeToCheck) res = (TDomainType)smth
  if (res == null) throw ex with errorMsg

Answer 2

首先定义公共接口

public interface IExtractor
{
    string RecordType { get; }
    string ErrorMessage { get; }
    string GetValue(object record);
}

接下来创建实现

class MxRecordExtractor : IExtractor
{
    public string RecordType => "Mx";

    public string ErrorMessage => DomainRegistrationCore.Models.DomainRecordType.MX;

    public string GetValue(object record)
    {
        return ((Microsoft.Graph.DomainDnsMxRecord)record).MailExchange;
    }
}

class VerificationRecordExtractor : IExtractor
{
    public string RecordType => "Txt";

    public string ErrorMessage => DomainRegistrationCore.Models.DomainRecordType.TXT;

    public string GetValue(object record)
    {
        return ((Microsoft.Graph.DomainDnsTxtRecord)record).Text;
    }
}

稍后创建方法的私有抽象版本：

private async Task<string> ExtractForDomainAsync(string domain, IExtractor extractor)
{
    try
    {
        var records = (await _graphClient.Domains[domain].VerificationDnsRecords.Request().GetAsync());
        string extractedValue = String.Empty;

        foreach (var record in records)
        {
            if (record.RecordType == extractor.RecordType)
            {
                extractedValue = extractor.GetValue(record);
                break;
            }
        }

        if (String.IsNullOrWhiteSpace(extractedValue))
            throw new DomainRecordNotFoundException(extractor.ErrorMessage);

        return extractedValue;
    }
    catch (ServiceException graphEx)
    {
        if (graphEx.StatusCode == System.Net.HttpStatusCode.NotFound)
        {
            throw new DomainNotFoundException();
        }

        throw new UnknownException(graphEx.StatusCode, graphEx.Error.Message);
    }
}

最后修改现有的方法来使用我们常用的方法：

public Task<string> GetMxRecordForDomainAsync(string domain)
{
    return ExtractForDomainAsync(domain,  new MxRecordExtractor());
}

public Task<string> GetVerificationRecordForDomainAsync(string domain)
{
    return ExtractForDomainAsync(domain, new VerificationRecordExtractor());
}

C#：如何在没有 "copy/paste" 代码的情况下重写它

C#: How to rewrite it without "copy/paste" code

c#

delegates

copy-paste