c# 带有自定义类型转换器的propertygrid，无法输入字符串

Question

我有一个可以以英寸或毫米为单位的测量类，现在使用可扩展类型转换器更改测量有点烦人，所以我想创建一个自定义的。问题是，propertygrid 似乎忽略了它。我放了断点，但什么都没有被调用。这是代码：

[TypeConverter(typeof(MeasurementConverter))]
public class Measurement
{
    double mm;
    public bool IsMM
    {
        get; set;
    }

    public double Inches
    {
        get { return mm / 25.4; }
        set { mm = value * 25.4; IsMM = false; }
    }
    public double Millimeters
    {
        get { return mm; }
        set { mm = value; IsMM = true; }
    }

    public Measurement(double value = 0, bool ismm = true)
    {
        if(ismm)
        {
            Millimeters = value;
        }
        else
        {
            Inches = value;
        }
    }

    public override string ToString()
    {
        if(IsMM)
        {
            return Millimeters.ToString(SVGElement.doubleFormat) + "mm";
        }
        else
        {
            return Inches.ToString(SVGElement.doubleFormat) + "in";
        }
    }
}

public class MeasurementConverter : TypeConverter
{
    public override bool CanConvertTo(ITypeDescriptorContext context, Type destinationType)
    {
        return typeof(string) == destinationType;
    }

    public override object ConvertTo(ITypeDescriptorContext context, CultureInfo culture, object value, Type destinationType)
    {
        if(destinationType == typeof(string))
        {
            Measurement m = value as Measurement;
            return m.ToString();
        }
        return base.ConvertTo(context, culture, value, destinationType);
    }

    public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
    {
        return typeof(string) == sourceType;
    }

    public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, object value)
    {
        string str = value as string;
        if(str != null)
        {
            var tmp = context.Instance;
            Measurement m = new Measurement();
            if(str.EndsWith("mm"))
            {
                m.Millimeters = double.Parse(str.Substring(0, str.Length - 2));
            }
            else if(str.EndsWith("in"))
            {
                m.Inches = double.Parse(str.Substring(0, str.Length - 2));
            }
            else //assume mm
            {
                try
                {
                    m.Millimeters = double.Parse(str);
                }
                catch { }
            }
            return m;
        }
        return base.ConvertFrom(context, culture, value);
    }
}

我无法在属性网格中输入字符串。它只是显示 toString() 返回的内容。

Answer 1

我是个 dingus，但在包含它们的类中的属性本身上仍有一个 typeconverter 属性。