How to create an option of type string, but available values must be is in a runtime given collection

[lsoft]

Hello.

I want to have an option

        [Category("My category")]
        [DisplayName("My name")]
        [Description("My description")]
        [DefaultValue("")]
        public string MyOption { get; set; } = "";

and I want to provide an available set of values for MyOption at runtime. I can't figure out it is possible or not.

Any ideas are welcome.

Thanks!

[mrlacey]

I want to provide an available set of values for MyOption at runtime. I can't figure out it is possible or not.

Use an enum rather than a string?

[lsoft]

@mrlacey Not an option. The set is available at runtime only (from the database).

[mrlacey]

Then an alternative might be what I do here

Which is to override OnApply and OnClosed in the options grid and validate the entered strings and reset to a default if something invalid is entered.
I don't know a way to dynamically populate a list in a default options grid without creating custom UI.

[lsoft]

@mrlacey thanks for idea! I'll take a look.

[reduckted]

Because the options are shown in a PropertyGrid*, which uses type descriptors and converters to get the properties to display, this can be achieved using a TypeConverter. I've created #554 to demonstrate this. The full code is in that PR, but I'll post the relevant parts here.

First, you need to change the type of the property to some type that wraps the string. In my example I called it RuntimeEnumProxy. It simply stores the string value.

public class RuntimeEnumProxy {
    public RuntimeEnumProxy(string value) {
        Value = value;
    }

    public string Value { get; }

    public override string ToString() {
        return Value;
    }
}

In the options type, add a TypeConverterAttribute to the property:

[Category("My category")]
[DisplayName("Runtime Enum")]
[Description("These enum values are defined at runtime")]
[TypeConverter(typeof(RuntimeEnumTypeConverter))]
public RuntimeEnumProxy RuntimeEnum { get; set; } = new RuntimeEnumProxy("");

You'll also need to override the SerializeValue and DeserializeValue methods. You might be able to avoid this if you can work out how the XmlSerializer will serialize the wrapper type, but I couldn't be bothered.

The TypeConverter is where you can define your "enum" values. You need to handle the ConvertFrom and ConvertTo methods to convert between the wrapper type and string, but that's pretty simple. The key methods are GetStandardValuesSupported, GetStandardValuesExclusive and GetStandardValues.

public override bool GetStandardValuesSupported(ITypeDescriptorContext context) => true;

public override bool GetStandardValuesExclusive(ITypeDescriptorContext context) => true;

public override StandardValuesCollection GetStandardValues(ITypeDescriptorContext context)
{
    return new StandardValuesCollection(
        new[] {
            new RuntimeEnumProxy("Alpha"),
            new RuntimeEnumProxy("Beta"),
            new RuntimeEnumProxy("Gamma"),
            new RuntimeEnumProxy("Delta")
        }
    );
}

And the end result is this:

* I'm not sure if it's actually a PropertyGrid, but it behaves the same way. 🤷‍♂️

[mrlacey]

That's awesome!

[lsoft]

@reduckted fantastic! Thank you!