Typeconverter does not work in asp.net core

问题

I have Amount stored in the database as decimal. I want to show that value on UI with thousand separator. I can add [DisplayFormat(DataFormatString = "{0:N2}", ApplyFormatInEditMode = true)] attribute on amount property and that would display number with thousand separator however when i POST the value back to server, the MVC model binding would not work because of commas.

I have created a custom type converter that converts from decimal to string and then string to decimal

public class NumberConverter : TypeConverter
{
    public override bool CanConvertFrom(
        ITypeDescriptorContext context,
        Type sourceType)
    {
        if (sourceType == typeof(decimal))
        {
            return true;
        }
        return base.CanConvertFrom(context, sourceType);
    }
    public override object ConvertFrom(ITypeDescriptorContext context,
        CultureInfo culture, object value)
    {
        if (value is decimal)
        {
            return string.Format("{0:N2}", value);
        }
        return base.ConvertFrom(context, culture, value);
    }
    public override bool CanConvertTo(ITypeDescriptorContext context,
        Type destinationType)
    {
        if (destinationType == typeof(decimal))
        {
            return true;
        }
        return base.CanConvertTo(context, destinationType);
    }
    public override object ConvertTo(ITypeDescriptorContext context,
        CultureInfo culture, object value, Type destinationType)
    {
        if (destinationType == typeof(decimal) && value is string)
        {
            return Scrub(value.ToString());
        }
        return base.ConvertTo(context, culture, value, destinationType);
    }

    private decimal Scrub(string modelValue)
    {
        NumberStyles _currencyStyle = NumberStyles.Currency;
        CultureInfo _culture = new CultureInfo("en-US");

        var modelDecimal = 0M;
        decimal.TryParse(
           modelValue,
           _currencyStyle,
           _culture,
           out modelDecimal
       );

        return modelDecimal;
    }
}

and then i applied it on one of the model property. Note that model may have other decimal properties which may not required this conversion.

public class MyModel
{

    [TypeConverter(typeof(NumberConverter))]
    [Display(Name = "Enter Amount")]
    public decimal Amount { get; set;}

    public string Name { get; set; }
}

Index.cshtml

<form asp-action="submit" asp-controller="home">
    @Html.EditorFor(m => m.Amount)
    <button type="submit" class="btn btn-primary">Save</button>
</form>

However the converter code never gets fired. When i put break point in NumberConverter none of the break point hit. Do i need to register type converter anywhere? I am using asp.net core.

回答1:

Based on my observations asp.net core doesn't take into account properties decorated by TypeConverters.

So it only supports TypeConverters that are decorating actual type class declaration.

Works

[TypeConverter(typeof(MyModelStringTypeConverter))]
public class MyModel
{

}

Doesn't work

public class OtherModel
{
    [TypeConverter(typeof(MyModelStringTypeConverter))]
    public MyModel MyModel { get;set; }
}

来源：https://stackoverflow.com/questions/43378709/typeconverter-does-not-work-in-asp-net-core