C#：更好的编码方式？

Question

我有一个代码块来处理我的应用程序中的异常，它使用 if/else 块来获取消息内容。
我的代码如下：

// define variable to hold exceptions...
var exceptionMessage = new StringBuilder();  
// based on the exception type...  
if (expType == typeof(EntityValidationException))  
{  
    // append the relevant message to the text...  
    exceptionMessage.Append(exception.InnerException.Message);  
}  
else if (expType == typeof(ValidationException))  
{  
    // This is the type of error generated when entities are validated  
    var validationException = (ValidationException)exception;  
    exceptionMessage.Append(validationException.InnerException.Message);  
}  
else if (expType == typeof(DomainSecurityException))  
{  
    // These are security breaches  
    var domainSecurityException = (DomainSecurityException)exception;  
    exceptionMessage.Append(domainSecurityException.InnerException.Message);  
}  
else if (expType == typeof(DomainInternalMessageException))  
{  
    // These are the type of errors generated a System.Exception occurs and is  
    // converted by the exception handling policy to a more friendly format  
    var domainInternalMessageException = (DomainInternalMessageException)exception;  
    exceptionMessage.Append(domainInternalMessageException.ExceptionMessage);  
}
else  
{  
    exceptionMessage.AppendFormat(ErrorMessagesRes.Standard_Error_Format, "Unknown error", exception.InnerException.Message);   
}  
// this shows the message as an alert popup...  
this.DisplayJavascriptMessage(exceptionMessage.ToString());

这已经从原始版本进行了改进，但只是想看看是否有针对此代码的更简洁、更可重用的解决方案。
提前感谢
马丁

Answer 1

假设这是一个传递异常对象的例程（并且不直接参与 try catch 块）并假设“异常”对象最终派生自 Exception，您可以稍微精简一下代码

// define variable to hold exceptions...
            var exceptionMessage = new StringBuilder();

            // based on the exception type...  
            if (exception is EntityValidationException || exception is ValidationException || exception is DomainSecurityException)
            {
                // append the relevant message to the text...  
                exceptionMessage.Append(exception.InnerException.Message);
            }

            else if (expType == typeof(DomainInternalMessageException))
            {
                // These are the type of errors generated a System.Exception occurs and is  
                // converted by the exception handling policy to a more friendly format  
                var domainInternalMessageException = (DomainInternalMessageException)exception;
                exceptionMessage.Append(domainInternalMessageException.ExceptionMessage);
            }
            else
            {
                exceptionMessage.AppendFormat(ErrorMessagesRes.Standard_Error_Format, "Unknown error", exception.InnerException.Message);
            }
            // this shows the message as an alert popup...  
            this.DisplayJavascriptMessage(exceptionMessage.ToString());

Answer 2

    var exceptionMessage = new StringBuilder();  

    try
    {
    }
    catch(EntityValidationException exc)
    {  
        exceptionMessage.Append(exc.InnerException.Message);  
    }  
    catch(ValidationException exc)  
    {  
        exceptionMessage.Append(exc.InnerException.Message);  
    }  
    ....

确保 catch 块按照从最不通用到最通用的正确顺序排列。

Answer 3

public static Exception On<T>(this Exception e, Action<T> action)
{
    if(e is T)
        action((T)e);

    return e;
}

exception.
    On<ValidationException>(e => exceptionMessage.Append(e.InnerException.Message)).
    On<DomainInternalMessageException>(e => ...);

Answer 4

每当我看到那些if else if 声明时，我认为这必须更容易完成。在某些情况下 switch 语句会有所帮助，但正如 this question 已经说过的那样，无法打开 Type。

所以我常用的另一种解决方法是某种Dictionary<Type, something>。 something 的位置取决于我想做什么。最适合您的案例的匹配结构可能类似于Dictionary<Type, Func<Exception, string>>，可以在您的案例中使用，如下所示：

Dictionary<Type, Func<Exception, string>> _FunctorsForType;

private void InitializeFunctorsForType()
{
    _FunctorsForType = new Dictionary<Type, Func<Exception, string>>();

    // Add a normal function
    _FunctorsForType.Add(typeof(ArgumentException), (Func<Exception, string>)ForArgumentException);

    // Add as lambda
    _FunctorsForType.Add(typeof(InvalidCastException), (ex) =>
        {
            // ToDo: Whatever you like
            return ex.Message;
        });
}

private string ForArgumentException(Exception ex)
{
    var argumentException = ex as ArgumentException;

    if (argumentException == null)
    {
        throw new ArgumentException("Exception must be of type " + typeof(ArgumentException).Name);
    }

    // ToDo: Whatever you like
    return ex.Message;
}

private void Usage(Type type)
{
    Func<Exception, string> func;

    if (!_FunctorsForType.TryGetValue(type, out func))
    {
        throw new ArgumentOutOfRangeException("Exception type " + type.Name + " is not supported.");
    }

    var message = func(new NullReferenceException());

    // ToDo: Whatever you have to do with your message
}

因此，通过这种结构，您不必将所有的智慧都投入到一个大的 if-else 语句中。相反，您可以将它们放在单独的函数中（可能在不同的类中），以便更好地组织如何处理您希望支持的每种类型。

Answer 5

string exceptionMessage;
if (expType == typeof(EntityValidationException) || 
    expType == typeof(ValidationException) ||
    expType == typeof(DomainSecurityException))
  exceptionMessage = exception.InnerException.Message;
else if (expType == typeof(DomainInternalMessageException))  
 exceptionMessage = ((DomainInternalMessageException)exception).ExceptionMessage;
else  
 exceptionMessage = string.Format(ErrorMessagesRes.Standard_Error_Format, "Unknown error", exception.InnerException.Message);  

this.DisplayJavascriptMessage(exceptionMessage);

有点压缩，没有 cmets。