Can't get RadzenDropDown to bind to a list of strings 'Specified cast is not valid.'

Radzen.Blazor Components
1

I'm getting the following error with the dropdown control. It loads fine, populates the list fine, the initial values from the data are selected. But if I try to change the selection, I get the following:

crit: Microsoft.AspNetCore.Components.WebAssembly.Rendering.WebAssemblyRenderer[100]
Unhandled exception rendering component: Specified cast is not valid.
System.InvalidCastException: Specified cast is not valid.
at Radzen.DropDownBase1.<SelectItem>d__100[[System.Collections.Generic.List1[[System.String, System.Private.CoreLib, Version=6.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]], System.Private.CoreLib, Version=6.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]].MoveNext()

The data 'roles' is a List of string, the thing I'm trying to bind to 'editUser.roles' is also a List of string. I don't get what it's trying to cast to throw this error.

<RadzenDropDown
id="roles"
Class="form-control"
@bind-Value=@editUser.Roles
Multiple="true"
SelectAllText="Select All"
Placeholder="Select..."
Data="@roles" />

2

This is exactly how the DropDown is bound in a sample app with security generated by Radzen:

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You can check it for reference.

3

Where do I find that example? What is '@roles' there, is it a list of strings? What type is 'user.roleNames'?

I'm not using your code generator thing, just the component library in visual studio.

4

You can generate it with our generator thing.

It's IEnumerable<string>

1 Like
5

Is what I'm pointing out a bug in the RadzenDropDown control, or am I missing something about how it's meant to work? Can it work with lists or does it specifically need IEnumerable?

I can't change it from List of Role to IEnumerable of Role, because that breaks the EF mapping on the database, so I don't know whether that would fix it.

6

It needs specifically IEnumerable<>.

Usually EF mapping works normally with IEnumerable<> - this is how actually Radzen EF context and models are generated.

7

This doesn't work with entity framework 6 and Azure Cosmos Db. This is the error you get if you try that:

System.InvalidOperationException: 'The property 'ApplicationUser.Roles' could not be mapped because it is of type 'IEnumerable', which is not a supported primitive type or a valid entity type. Either explicitly map this property, or ignore it using the '[NotMapped]' attribute or by using 'EntityTypeBuilder.Ignore' in 'OnModelCreating'.'

Where as it works perfectly fine as a list.

Is it within the realms of possibility in future versions of Radzen that dropdown could be a bit more flexible in what it'll bind to? A list implements IEnumerable after all.

8

We accept pull requests!

UPDATE: Actually I've made support for this case - it will be available with our update before the end of the week:

1 Like
9

Amazing, thank you, that's great. In the mean time I've worked around it with a non-mapped property on my model that sets the mapped one and then bound to that on the dropdown control e.g.:

public List<string> Roles { get; set; } = new List<string>();

[NotMapped]
public IEnumerable<string> RolesEnumerable
{
    get
    {
        return this.Roles;
    }
    set
    {
        this.Roles = value.ToList();
    }
}

That lets me work around it for now.

I'll hopefully try the updated version soon (though my partner is due to give birth any day now, so might be a while!)