在捕获到某些错误的情况下如何打破循环

Question

问：

如果事件中捕获到一些异常，我想中断循环。

代码：

XmlDocument x = new XmlDocument();
x.Load(targetFileName);

XmlReaderSettings settings = new XmlReaderSettings();
settings.CloseInput = true;
settings.ValidationEventHandler += Handler;

settings.ValidationType = ValidationType.Schema;
settings.Schemas.Add(null,System.Web.HttpContext.Current.Server.MapPath("~/importSchema/IntialSchema.xsd"));
settings.ValidationFlags =
     XmlSchemaValidationFlags.ReportValidationWarnings |
XmlSchemaValidationFlags.ProcessIdentityConstraints |
XmlSchemaValidationFlags.ProcessInlineSchema |
XmlSchemaValidationFlags.ProcessSchemaLocation;

using (StreamReader str_reader = new StreamReader(targetFileName))
{

    using (XmlReader validatingReader = XmlReader.Create(str_reader, settings))
    {
        while (validatingReader.Read())
        {
            //I wanna to break this loop if there is some caught error .
        }
    }
}

---

private static void Handler(object sender, ValidationEventArgs e)
{

    if (e.Severity == XmlSeverityType.Error || e.Severity == XmlSeverityType.Warning)
    {
        try
        {
            throw new Exception(
                 String.Format("Line: {0}, Position: {1} \"{2}\"",
                     e.Exception.LineNumber, e.Exception.LinePosition, e.Exception.Message));
        }
        catch (Exception ee)
        {
            Common.ErrMappingForInformix.WriteLog(ee.Message);
            ScheduleForm sf = new ScheduleForm();
            sf.ShowStatus("Error,Invalid xml file", "error", "", 1);

        }

    }

}

---

#编辑1：

XmlDocument x = new XmlDocument();
x.Load(targetFileName);

XmlReaderSettings settings = new XmlReaderSettings();
settings.CloseInput = true;
settings.ValidationEventHandler += (senderValidation, ee) =>
{
    if (ee.Severity == XmlSeverityType.Error || ee.Severity == XmlSeverityType.Warning)
    {
        try
        {
            this.validationFailed = true;
            throw new Exception(
                 String.Format("Line: {0}, Position: {1} \"{2}\"",
                     ee.Exception.LineNumber, ee.Exception.LinePosition, ee.Exception.Message));
        }
        catch (Exception ex)
        {

            Common.ErrMappingForInformix.WriteLog(ex.Message);
            this.ShowStatus("Error", "error", "", 1);
        }

    }
};

settings.ValidationType = ValidationType.Schema;
settings.Schemas.Add(null, System.Web.HttpContext.Current.Server.MapPath("~/importSchema/IntialSchema.xsd"));
settings.ValidationFlags =
     XmlSchemaValidationFlags.ReportValidationWarnings |
XmlSchemaValidationFlags.ProcessIdentityConstraints |
XmlSchemaValidationFlags.ProcessInlineSchema |
XmlSchemaValidationFlags.ProcessSchemaLocation;

using (StreamReader str_reader = new StreamReader(targetFileName))
{

    using (XmlReader validatingReader = XmlReader.Create(str_reader, settings))
    {
        while (validatingReader.Read())
        {
            //Loop through the document
            if (validationFailed)
            {
                break;
            }

        }
    }
}

它打破了循环，但不执行事件处理程序。

Answer 1

您可以设置一个标志来指示 Handler 方法中存在错误，然后检测该标志并使用 break;（如果已设置）。

在这种情况下，最好对验证处理程序使用内联匿名委托，这样您就不需要向包含方法的类添加新的成员变量。 （如果类仅处理XML读取/验证，添加成员变量并不是那么糟糕）

编辑：匿名内联委托意味着您可以添加一个不必位于单独的事件处理程序中的事件处理程序方法，基本上。例如：

bool validationFailed = false; // outside of the handler
settings.ValidationEventHandler += (sender, e) =>
{
    if (e.Severity == XmlS....
    // set validationFailed = true; in here to signal failure
};

// then detect validationFailed being true to know if/when to break;

Answer 2

我只是将异常抛出到处理程序中，并在捕获它时中断控制流。但是，也要避免抛出过于通用的异常类型：更好的是使用自定义异常：

class XmlValidationFailedException : Exception {
   public XmlValidationFailedException(string message, Exception innerException) : base(message, innerException) {}

   // as per Kieren's comment, make sure this exception type is defined according to best practices
}


private static void Handler(object sender, ValidationEventArgs e)
{

    if (e.Severity == XmlSeverityType.Error || e.Severity == XmlSeverityType.Warning)
    {
        string message = String.Format("Line: {0}, Position: {1} \"{2}\"",
                     e.Exception.LineNumber, e.Exception.LinePosition, e.Exception.Message)

        throw new XmlValidationFailedException(message);
    }

然后你的循环可以变成这样：

try
{
   while (validatingReader.Read())
   {
       // do logic
   }
}
catch (XmlValidationException ex)
{
    // handle the error (log, show, ...) 
    return;
}