Question

我需要覆盖XMLWriter的方法＆＃34; WriteElementString＆＃34;如果值为空，则不写元素，下面的代码不起作用，尝试覆盖和新关键字，但它仍然转到框架方法。< / p>

public static void WriteElementString(this XmlWriter writer,
                                      string localName,
                                      string value)
{
    if (!string.IsNullOrWhiteSpace(value))
    {
        writer.WriteStartElement(localName);
        writer.WriteString(value);
        writer.WriteEndElement();
    }
}

答案很接近但正确的解决方案是：

public abstract class MyWriter : XmlWriter
{
    private readonly XmlWriter writer;
    public Boolean skipEmptyValues;

    public MyWriter(XmlWriter writer)
    {
        if (writer == null) throw new ArgumentNullException("Writer");
        this.writer = writer;
    }

    public new void WriteElementString(string localName, string value)
    {
        if (string.IsNullOrWhiteSpace(value) && skipEmptyValues)
        {
            return;
        }
        else
        {
            writer.WriteElementString(localName, value);
        }
    }
}

Answer 1

您需要创建一个装饰XmlWriter的对象，以实现您的目标。 More on the Decorator Pattern

public class MyXmlWriter : XmlWriter
{
    private readonly XmlWriter writer;

    public MyXmlWriter(XmlWriter writer)
    {
        if (writer == null) throw new ArgumentNullException("writer");
        this.writer = writer;
    }

    // This will not be a polymorphic call
    public new void WriteElementString(string localName, string value)
    {
        if (string.IsNullOrWhiteSpace(value)) return;

        this.writer.WriteElementString(localName, value);
    }

    // the rest of the XmlWriter methods implemented using Decorator Pattern
    // i.e.
    public override void Close()
    {
        this.writer.Close();
    }
    ...
}

using (var writer = XmlWriter.Create(XMLBuilder, XMLSettings))
using (var myWriter = new MyXmlWriter (writer))
{
    // use myWriter in here to construct XML
}

您要做的是使用扩展方法覆盖方法，这不是他们想要做的。请参阅扩展方法MSDN页面上的Binding Extension Methods at Compile Time部分编译器将始终将WriteElementString解析为XmlWriter实现的实例。您需要手动调用扩展方法XmlWriterExtensions.WriteElementString(writer, localName, value);，以便您的代码可以执行。

需要覆盖XMLWriter的方法

1 个答案: