Combine ExpandableObjectConverter with Drop Down List

Question

I have a nullable property in my class and I want user to be able to create its instance using PropertyGrid. Which I did using ExpandableObjectConverter.

When instance is created it automatically appears in PropertyGrid with posibility to expand it and change its properties' values.

Still I need to type some string to create a new instance.

That is why I am wondering if it is possible to combine ExpandableObjectConverter with DropDownList. So user would be able to select one of the existing values.

Answer 1

You need to create a new ExpandableObjectConverter, supporting standard values.

Example

As an example, lets say, xlass A has a property of type B and we like to let the user to choose some predefined values for B from a drop-down list in property grid.

After you select something from dropdown, the B will be initialized and you still can edit C:

Here is the definition for A and B:

public class A
{
    [TypeConverter(typeof(BConverter))]
    public B B { get; set; }
}
public class B : ICloneable
{
    [RefreshProperties(RefreshProperties.All)]
    public string C { get; set; }
    public object Clone()
    {
        return new B { C = this.C };
    }
    public override string ToString()
    {
        return C;
    }
}

Here is the custom ExpandableObjectConverter:

public class BConverter : ExpandableObjectConverter
{
    B[] values = new B[] { new B { C = "Something" }, new B { C = "Something else" } };
    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, 
        System.Globalization.CultureInfo culture, object value)
    {
        var result = values.Where(x => $"{x}" == $"{value}").FirstOrDefault();
        if (result != null)
            return result.Clone();
        return base.ConvertFrom(context, culture, value);
    }
    public override bool GetStandardValuesSupported(ITypeDescriptorContext c)
    {
        return true;
    }
    public override bool GetStandardValuesExclusive(ITypeDescriptorContext c)
    {
        return true;
    }
    public override StandardValuesCollection GetStandardValues(ITypeDescriptorContext c)
    {
        return new StandardValuesCollection(values);
    }
}