Darp.CommunityToolkit.MvvmValidator 0.1.1

Darp.CommunityToolkit.MvvmValidator

DataAnnotations validation for CommunityToolkit.Mvvm view models that works with trimming and Native AOT. A source generator writes the validation code, so nothing is discovered with reflection at runtime.

dotnet add package Darp.CommunityToolkit.MvvmValidator

Requirements:

• .NET 10
• View models and their containing types are partial. A code fix adds missing modifiers.
• Attributes that only target properties, like [Compare], need [property: ...] on [ObservableProperty] fields.

Usage

Derive from ValidatingObservableObject instead of ObservableValidator and make the class partial:

using System.ComponentModel.DataAnnotations;
using CommunityToolkit.Mvvm.ComponentModel;
using Darp.MvvmValidator;

public partial class SignUpViewModel : ValidatingObservableObject
{
    public SignUpViewModel() => ValidateAllProperties();

    [ObservableProperty]
    [Required]
    [StringLength(20, MinimumLength = 3)]
    [Display(Name = "User name")]
    public partial string? UserName { get; set; }

    [ObservableProperty]
    [Required]
    public partial string? Password { get; set; }

    [ObservableProperty]
    [Compare(nameof(Password))]
    public partial string? ConfirmPassword { get; set; }

    [CustomValidation(typeof(SignUpViewModel), nameof(ValidateInvite))]
    public string? InviteCode
    {
        get;
        set => SetProperty(ref field, value);
    }

    public static ValidationResult? ValidateInvite(string? code, ValidationContext context) =>
        code is null or "WELCOME" ? ValidationResult.Success : new ValidationResult("Unknown invite code");
}

<details> <summary>Generated code</summary>

// <auto-generated/>
#nullable enable
partial class SignUpViewModel
{
    private static readonly global::System.ComponentModel.DataAnnotations.RequiredAttribute __dmv_rule0_0 = new global::System.ComponentModel.DataAnnotations.RequiredAttribute();
    private static readonly global::System.ComponentModel.DataAnnotations.StringLengthAttribute __dmv_rule0_1 = new global::System.ComponentModel.DataAnnotations.StringLengthAttribute(((int)(20))) { MinimumLength = ((int)(3)) };
    private static readonly global::System.ComponentModel.DataAnnotations.DisplayAttribute __dmv_display0 = new global::System.ComponentModel.DataAnnotations.DisplayAttribute() { Name = "User name" };
    private static readonly global::System.ComponentModel.DataAnnotations.RequiredAttribute __dmv_rule1_0 = new global::System.ComponentModel.DataAnnotations.RequiredAttribute();

    /// <inheritdoc />
    [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
    protected override bool TryValidatePropertyCore(string propertyName, global::System.Collections.Generic.ICollection<global::System.ComponentModel.DataAnnotations.ValidationResult> errors)
    {
        switch (propertyName)
        {
            case "UserName":
                __dmv_validate0(this.UserName, errors);
                return true;
            case "Password":
                __dmv_validate1(this.Password, errors);
                return true;
            case "ConfirmPassword":
                __dmv_validate2(this.ConfirmPassword, errors);
                return true;
            case "InviteCode":
                __dmv_validate3(this.InviteCode, errors);
                return true;
            default:
                return base.TryValidatePropertyCore(propertyName, errors);
        }
    }

    /// <inheritdoc />
    [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
    protected override void ValidateAllPropertiesCore()
    {
        base.ValidateAllPropertiesCore();
        ValidateProperty("UserName");
        ValidateProperty("Password");
        ValidateProperty("ConfirmPassword");
        ValidateProperty("InviteCode");
    }

    /// <inheritdoc />
    [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
    protected override void ValidateDependentPropertiesCore(string propertyName)
    {
        switch (propertyName)
        {
            case "Password":
                RevalidateIfValidated("ConfirmPassword");
                break;
        }
        base.ValidateDependentPropertiesCore(propertyName);
    }

    private void __dmv_validate0(string? value, global::System.Collections.Generic.ICollection<global::System.ComponentModel.DataAnnotations.ValidationResult> errors)
    {
        global::System.ComponentModel.DataAnnotations.ValidationContext context = CreateValidationContext("UserName", __dmv_display0.GetName());
        global::System.ComponentModel.DataAnnotations.ValidationResult? result;
        result = __dmv_rule0_0.GetValidationResult(value, context);
        if (result is not null)
        {
            errors.Add(result);
            return;
        }
        result = __dmv_rule0_1.GetValidationResult(value, context);
        if (result is not null)
        {
            errors.Add(result);
        }
    }

    private void __dmv_validate1(string? value, global::System.Collections.Generic.ICollection<global::System.ComponentModel.DataAnnotations.ValidationResult> errors)
    {
        global::System.ComponentModel.DataAnnotations.ValidationContext context = CreateValidationContext("Password", null);
        global::System.ComponentModel.DataAnnotations.ValidationResult? result;
        result = __dmv_rule1_0.GetValidationResult(value, context);
        if (result is not null)
        {
            errors.Add(result);
            return;
        }
    }

    private void __dmv_validate2(string? value, global::System.Collections.Generic.ICollection<global::System.ComponentModel.DataAnnotations.ValidationResult> errors)
    {
        global::System.ComponentModel.DataAnnotations.ValidationContext context = CreateValidationContext("ConfirmPassword", null);
        global::System.ComponentModel.DataAnnotations.ValidationResult? result;
        result = ValidateCompare(value, this.Password, "Password", null, context);
        if (result is not null)
        {
            errors.Add(result);
        }
    }

    private void __dmv_validate3(string? value, global::System.Collections.Generic.ICollection<global::System.ComponentModel.DataAnnotations.ValidationResult> errors)
    {
        global::System.ComponentModel.DataAnnotations.ValidationContext context = CreateValidationContext("InviteCode", null);
        global::System.ComponentModel.DataAnnotations.ValidationResult? result;
        result = CompleteCustomValidationResult(global::SignUpViewModel.ValidateInvite(value, context), null, context);
        if (result is not null)
        {
            errors.Add(result);
        }
    }
}

</details>

Behavior

• Properties with validation attributes are validated whenever they change, before PropertyChanged reaches subscribers. [NotifyDataErrorInfo] and SetProperty(..., validate: true) are not needed.
• Results match Validator.TryValidateProperty, including [CustomValidation], [Compare] and resource-based messages.
• When a [Compare] target changes, the comparing property is validated again, unless it is still untouched.
• ValidateAllProperties and ClearErrors work as in ObservableValidator. SetErrors adds results of asynchronous or server-side validation.

Diagnostics

The package turns off the toolkit's MVVMTK0006, which only accepts ObservableValidator, and reports these instead:

[Compare], [MinLength], [MaxLength] and [Length] make the trim analyzer and the trimmer warn where they are applied. The package suppresses these warnings when the generated code avoids the reflection they warn about. For properties with hand-written accessors or a field initializer, the warnings stay, because suppressing them would also hide warnings in that code.

Development

• Format with CSharpier: dotnet tool restore, then dotnet csharpier format .
• Runtime tests also run as a Native AOT executable in CI, which proves the generated code is trim safe.
• Generator tests snapshot the generated code with Verify.
• Releases come from Conventional Commits via release-please. Every pull request publishes a preview package to https://nuget.pkg.github.com/rosslight/index.json.