Exception netstandard 1.4 PCL

I’m trying to to validate a ViewModel in a netstandard 1.4 PCL. The code below crashes in the constructor of RegisterCmdValidator with an ArgumentException: “Cannot bind to the target method because its signature or security transparency is not compatible with that of the delegate type.”

This happens with 6.2.1 and the latest beta (6.4.0-beta9 at the time of writing).

Callstack:

at System.Reflection.RuntimeMethodInfo.CreateDelegateInternal(Type delegateType, Object firstArgument, DelegateBindingFlags bindingFlags, StackCrawlMark& stackMark) at System.Reflection.RuntimeMethodInfo.CreateDelegate(Type delegateType) at FluentValidation.Resources.StaticResourceAccessorBuilder.GetResourceAccessor(Type resourceType, String resourceName) in C:\projects\FluentValidation\src\FluentValidation\Resources\IResourceAccessorBuilder.cs:line 44 at FluentValidation.Resources.LocalizedStringSource…ctor(Type resourceType, String resourceName, IResourceAccessorBuilder resourceAccessorBuilder) in C:\projects\FluentValidation\src\FluentValidation\Resources\LocalizedStringSource.cs:line 40 at FluentValidation.Resources.LocalizedStringSource.CreateFromExpression(Expression1 expression, IResourceAccessorBuilder resourceProviderSelectionStrategy) in C:\projects\FluentValidation\src\FluentValidation\Resources\LocalizedStringSource.cs:line 68 at FluentValidation.DefaultValidatorOptions.<>c__DisplayClass10_02.<WithLocalizedMessage>b__0(PropertyRule config) in C:\projects\FluentValidation\src\FluentValidation\DefaultValidatorOptions.cs:line 185 at FluentValidation.Internal.RuleBuilder2.FluentValidation.Internal.IConfigurable<FluentValidation.Internal.PropertyRule,FluentValidation.IRuleBuilderOptions<T,TProperty>>.Configure(Action1 configurator) in C:\projects\FluentValidation\src\FluentValidation\Internal\RuleBuilder.cs:line 80 at FluentValidation.DefaultValidatorOptions.WithLocalizedMessage[T,TProperty](IRuleBuilderOptions2 rule, Expression1 resourceSelector, IResourceAccessorBuilder resourceAccessorBuilder) in C:\projects\FluentValidation\src\FluentValidation\DefaultValidatorOptions.cs:line 184 at FluentValidation.DefaultValidatorOptions.WithLocalizedMessage[T,TProperty](IRuleBuilderOptions2 rule, Expression1 resourceSelector) in C:\projects\FluentValidation\src\FluentValidation\DefaultValidatorOptions.cs:line 141 at ViewModels.RegistrationViewModel.RegisterCmdValidator…ctor(ICoreStrings coreStrings)

public class RegistrationViewModel
{
	...

    private readonly ICoreStrings coreStrings;

    class RegisterCmdValidator : AbstractValidator<RegistrationViewModel>
    {
        public RegisterCmdValidator(ICoreStrings coreStrings)
        {
            RuleFor(vm => vm.Password).NotEmpty().WithLocalizedMessage(() => FluentValidation.Resources.Messages.notempty_error);
            RuleFor(vm => vm.Password).Length(4, 15).WithLocalizedMessage(() => FluentValidation.Resources.Messages.length_error);
            RuleFor(vm => vm.ConfirmPassword).NotEmpty().WithLocalizedMessage(() => FluentValidation.Resources.Messages.notempty_error);

            // Crash
            RuleFor(vm => vm.ConfirmPassword).Must((vm, password) => vm.Password == password).WithLocalizedMessage(() => coreStrings.ValidationPasswordConfirmMismatch);

            // Works
            RuleFor(vm => vm.ConfirmPassword).Must((vm, password) => vm.Password == password).WithMessage(coreStrings.ValidationPasswordConfirmMismatch);
        }
    }

    readonly RegisterCmdValidator registerCmdValidator;

    private string email;

    public string Email
    {
        get { return email; }
        set { this.RaiseAndSetIfChanged(ref email, value); }
    }

    private string password;

    public string Password
    {
        get { return password; }
        set { this.RaiseAndSetIfChanged(ref password, value); }
    }

    private string confirmPassword;

    public string ConfirmPassword
    {
        get { return confirmPassword; }
        set { this.RaiseAndSetIfChanged(ref confirmPassword, value); }
    }
}

[oliverw]

Yeah it’s not really obvious right now that the lambda has some hidden requirements. I think your proposed changes are spot on.

[JeremySkinner]

This has caused confusion a few times…I guess it comes from using a lambda for something unusual which isn’t expected.

I’m thinking of changing this behaviour for the next version:

1. Add new WithLocalizedMessage(Type resourceType, string resourceName)
2. Deprecate WithLocalizedMessage(Expression<Func<string>>), with the above method being the recommended replacement
3. Add a new WithLocalizedMessage(Func<T, string>) that would work as you expect, and also provide access to the container model in the delegate

What do you think?