ReactiveUI 仅在用户输入更改时验证

Question

我是 ReactiveUI 的新手，所以我坚持这个问题，我的错误消息显示在页面开始，而不是在用户输入更改之后。

我想我对 ComplexRule 有疑问。所以这是我在 ViewModel 中的代码：

    public LoginViewModel(IScreen screen)
    {
        HostScreen = screen;
        NameRule = this.ValidationRule(
            viewModel => viewModel.UserName,
            name => name.Length > 2,
            "You must specify a valid name longer then 2 sybols.");

        //checks with Regexp password
        PasswordRule = this.ValidationRule(
            viewModel => viewModel.Password,
            password => PasswordValidator.Validate(password),
            "You must specify a valid password longer then 8 sybols with at least 1 digit, upper 
             case, lower case and special characters.");

        var nameAndPasswordRules = this
            .WhenAnyValue(
                x => x.UserName,
                x => x.Password,
                (name, password) => NameRule.IsValid && PasswordRule.IsValid);

        ComplexRule = this.ValidationRule(
            _ => nameAndPasswordRules,
            (vm, state) => !state ? "Username and Password should be both valid!" : string.Empty);

        var canNavigate = this.IsValid();

        NavigateToMainPage = ReactiveCommand.CreateFromObservable(() =>
        {
            return HostScreen.Router.NavigateAndReset.Execute(new MyTabbedViewModel(HostScreen));
        }, canNavigate);
    }

这是我的观点：

    public LoginView()
    {
        InitializeComponent();
        this.WhenActivated(disposables =>
        {
            this.Bind(ViewModel, vm => vm.UserName, v => v.username.Text)
                .DisposeWith(disposables);

            this.BindValidation(ViewModel, vm => vm.NameRule, v => v.usernameErrors.Text)
                .DisposeWith(disposables);

            this.Bind(ViewModel, vm => vm.Password, v => v.password.Text)
                .DisposeWith(disposables);

            this.BindValidation(ViewModel, vm => vm.PasswordRule, v => v.passwordErrors.Text)
                .DisposeWith(disposables);

            this.BindCommand(ViewModel, x => x.NavigateToMainPage, x => x.loginButton)
                .DisposeWith(disposables);
        });
    }

所以我试图在用户输入更改（密码/用户名）后实现验证并显示适当的消息。我从文档中获取了这个示例。

Answer 1

我尝试了几种方法并完成了这个。不确定这是否是最好的方法，但它有效（想听听你的意见，如果你知道如何做得更好。

我将 null 值分配给属性

[Reactive]
public string UserName { get; set; } = null;

[Reactive]
public string Password { get; set; } = null;

所以我们假设 null - 意味着它从未被使用过。

并将此类验证放在 ValidationRule 上

        var name = this
            .WhenAnyValue(x => x.UserName)
            .Select(x => x == null || x?.Length > 2);

        var password = this
            .WhenAnyValue(x => x.Password)
            .Select(x => x == null || PasswordValidator.Validate(x));

        var nameAndPasswordRules = this
            .WhenAnyValue(
                x => x.UserName,
                x => x.Password)
            .DefaultIfEmpty()
            .DistinctUntilChanged()
            .SkipWhile(item => !string.IsNullOrWhiteSpace(item.Item1) && !string.IsNullOrWhiteSpace(item.Item2))
            .Select(prop1 =>
                        !string.IsNullOrEmpty(prop1.Item1)
                        && this.NameRule.IsValid
                        && !string.IsNullOrEmpty(prop1.Item2)
                        && this.PasswordRule.IsValid);

        NameRule = this.ValidationRule(
            _ => name,
            (vm, state) => !state ? "You must specify a valid name longer then 2 sybols." : string.Empty);

        PasswordRule = this.ValidationRule(
            _ => password,
            (vm, state) => !state ? "You must specify a valid password longer then 8 sybols with at least 1 digit, upper case, lower case and special characters." : string.Empty);

        ComplexRule = this.ValidationRule(
            _ => nameAndPasswordRules,
            (vm, state) => !state ? "Username and Password should be both valid!" : string.Empty);

如你所见，我会 x == null || ... 意味着绕过第一次尝试，因为用户没有编辑条目

ReactiveUI 仅在用户输入更改时验证

ReactiveUI Validate only when user input changes

validation

reactiveui

xamarin.forms