Blazor ValidationMessage Failing

[aherrick]

I have a setup like below:

<label class="control-label">User</label>
<input class="form-control" @bind="@VM.Connector.ConnectorDetails[0]" />
<ValidationMessage For="@(() => VM.Connector.ConnectorDetails.ElementAt(0))" />

With ValidationMessage I'm getting the following error:

ArgumentException: The provided expression contains a MethodCallExpression2 which is not supported. FieldIdentifier only supports simple member accessors (fields, properties) of an object.

How can I support displaying the error message for the given element in the array?

[SteveSandersonMS]

Does the following not work?

<ValidationMessage For="@(() => VM.Connector.ConnectorDetails[0])" />

What's the reason why you needed to use ElementAt?

[aherrick]

Hey Steve. Not that I'm seeing. With the array accessor I'm seeing:

ArgumentException: The provided expression contains a InstanceMethodCallExpression1 which is not supported. FieldIdentifier only supports simple member accessors (fields, properties) of an object.

[SteveSandersonMS]

Oh wait, yeah, it can't work.

The expression you're providing is to populate a FieldIdentifier, which is an (object, propertyName) pair. It's essential that we have a meaningful value for propertyName since that's the key into the edit context dictionary for that field. It would be bad if we allowed the propertyName to be something like 0 (in your example) as that would result in mismatches if items were inserted/deleted from the collection.

So instead what you need to do is use a data structure where you have reference-typed objects with fields/properties. For example, ConnectionDetails could be a List<Connector>, where Connector has a property DetailsText, and then you'd use:

<ValidationMessage For="@(() => VM.Connector.ConnectorDetails[0].DetailsText)" />

This will work because VM.Connector.ConnectorDetails[0] would resolve as an object, and we'd know to use DetailsText as the property name.

[aherrick]

Thanks for the response! That's unfortunate as I'm not trying to create an object with a property of 1 just to support this situation. Since it can bind successfully to @VM.Connector.ConnectorDetails[0] I would assume we could link the validation message as well.

[aherrick]

@SteveSandersonMS Is there anyway I can create a unique FieldIdentifier.FieldName so on the back end when validation occurs I can distinguish between the following:

    <div class="form-group">
        <label class="control-label">@VM.Parent.Children[0].DataKey</label>
        <InputText class="form-control" @bind-value="@VM.Parent.Children[0].DataValue" />
        <ValidationMessage For="@(() => VM.Parent.Children[0].DataValue)" />
    </div>

    <div class="form-group">
        <label class="control-label">@VM.Parent.Children[1].DataKey</label>
        <InputText class="form-control" @bind-value="@VM.Parent.Children[1].DataValue" />
        <ValidationMessage For="@(() => VM.Parent.Children[1].DataValue)" />
    </div>

Both just register as DataValue so I can't programmatically match the field up to the validation message I'm generating (using FluentValidation)

Thank you!