C#如何实现类型转换器 [英] c# how to implement type converter

问题描述

我正在努力用C#实现一个简单的Type转换器.我遵循了本指南 https://msdn.microsoft.com/en-us/library/ayybcxe5.aspx

I am struggling to implement a simple Type converter in C#. I followed this guide https://msdn.microsoft.com/en-us/library/ayybcxe5.aspx

这是我的课程:

public class TestClass: TypeConverter
{
        public string Property1{ get; set; }
        public int Property2 { get; set; }
        public TestClass(string p1, int p2)
        {
            Property1= p1;
            Property2 = p2;
        }
        public override bool CanConvertFrom(ITypeDescriptorContext context,
        Type sourceType)
        {
            if (sourceType == typeof(string)) {
                 return true;
            }
            return base.CanConvertFrom(context, sourceType);
        }
        public override object ConvertFrom(ITypeDescriptorContext context,
         CultureInfo culture, object value)
        {
              if (value is string) {
                    return new TestClass ("", Int32.Parse(value.ToString()));
              }
              return base.ConvertFrom(context, culture, value);
        }
        public override object ConvertTo(ITypeDescriptorContext context,
        CultureInfo culture, object value, Type destinationType)
        {
            if (destinationType == typeof(string)) {
               return "___"
            }
            return base.ConvertTo(context, culture, value, destinationType);
        }
 }

我执行以下 TestClass(",, Int32.Parse(value.ToString())); ，因为现在我只对" 1231->这样的情况感兴趣;新的TestClass("，1231)

I do the following TestClass ("", Int32.Parse(value.ToString())); as for now I am only interested in such case as "1231" -> new TestClass("", 1231)

下面是给我一个例外的代码；

And here goes the code that gives me an exception;

TypeConverter converter=TypeDescriptor.GetConverter( typeof(TestClass));
Object lalala = converter.ConvertFromString("234");

此代码引发 NotSupportedException ，但我不知道为什么

This code throws NotSupportedException but I don't get why

推荐答案

您必须将此转换器附加到具有 TypeConverter 属性的类.
TypeDescriptor.GetConverter 获取该类的附加转换器.

You have to attach this converter to a class with the TypeConverter attribute.
TypeDescriptor.GetConverter Get the attached converter of the class.

您最好拆分课程:

[TypeConverter(typeof (TestClassConverter))]
public class TestClass
{
    public string Property1 { get; set; }
    public int Property2 { get; set; }
    public TestClass(string p1, int p2)
    {
        Property1 = p1;
        Property2 = p2;
    }
}

[TypeConverter(typeof (TestClassConverter))]
public class TestClassConverter : TypeConverter
{
    public override bool CanConvertFrom(ITypeDescriptorContext context,
    Type sourceType)
    {
        if (sourceType == typeof(string))
        {
            return true;
        }
        return base.CanConvertFrom(context, sourceType);
    }
    public override object ConvertFrom(ITypeDescriptorContext context,
     CultureInfo culture, object value)
    {
        if (value is string)
        {
            return new TestClass("", Int32.Parse(value.ToString()));
        }
        return base.ConvertFrom(context, culture, value);
    }
    public override object ConvertTo(ITypeDescriptorContext context,
    CultureInfo culture, object value, Type destinationType)
    {
        if (destinationType == typeof(string)) { return "___"; }
        return base.ConvertTo(context, culture, value, destinationType);
    }
}

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