表单单步执行不同的组件。对象引用未设置为对象的实例。在 Telerik.Blazor.Components.TelerikForm.IsValid（）

问：

我正在尝试将表单验证的不同步骤分离到不同的组件中。因此，例如，用户在一个步骤中填写个人信息，而用户必须在下一个步骤中填写有关教育的信息。

你将如何解决这个问题？

现在，我在 Telerik 有一个试用期，所以我遵循他们的 Wizard 组件进行表单集成。

错误

错误：System.NullReferenceException：对象引用未设置为对象的实例。 在 Telerik.Blazor.Components.TelerikForm.IsValid（） 在 C：\source\ApplicantSln\ApplicantTemp\Pages\Wizard\MainComponent.razor：第 50 行中的 ApplicantTemp.Pages.Wizard.MainComponent.OnRegistrationStepChange （WizardStepChangeEventArgs args） 在 System.RuntimeMethodHandle.InvokeMethod （对象目标、 Void** 参数、 签名 sig、 布尔值 isConstructor） 在 System.Reflection.MethodInvoker.Invoke （对象 obj、 IntPtr* 参数、 BindingFlags invokeAttr） --- 从上一个位置---结束堆栈跟踪 在 Microsoft.AspNetCore.Components.ComponentBase.CallStateHasChangedOnAsyncCompletion（任务任务） 在 Telerik.Blazor.Components.Common.BaseComponent.InvokeEvent[T] （EventCallback'1 eventCallback，T args） 在 Telerik.Blazor.Components.TelerikWizard.ChangeStep （Int32 newStepIndex） 在 Telerik.Blazor.Components.TelerikWizard.GoToNextPage（） 在 Microsoft.AspNetCore.Components.ComponentBase.CallStateHasChangedOnAsyncCompletion（任务任务） 在 Microsoft.AspNetCore.Components.RenderTree.Renderer.GetErrorHandledTask（任务任务ToHandle，组件状态owningComponentState）

    public void OnRegistrationStepChange(WizardStepChangeEventArgs args)
    {

        // Add debugging code to inspect the state of RegisterForm and other variables
        Console.WriteLine("OnRegistrationStepChange is called.");
        Console.WriteLine($"RegisterForm is {RegisterForm}");
        var isFormValid = RegisterForm.IsValid(); //ERROR FROM HERE!!!!!!!!
        if (!isFormValid)
        {
            IsRegistrationValid = false;
            args.IsCancelled = true;
        }
        else
        {
            IsRegistrationValid = true;
        }
    }

MainComponent.razor

@page "/reg"

@using System.ComponentModel.DataAnnotations

<TelerikWizard @bind-Value="@Value" OnFinish="@OnFinishHandler" Width="700px">
    <WizardSteps>
        <WizardStep Label="Registration" Icon="@FontIcon.User" OnChange="@OnRegistrationStepChange" Valid="@IsRegistrationValid">
            <Content>
                <RegistrationForm UserModel="@UserModel" RegisterForm="@RegisterForm" />
            </Content>
        </WizardStep>
        <WizardStep Label="Shipping address" Icon="@FontIcon.MapMarkerTarget" OnChange="@OnShippingStepChange" Valid="@IsShippingValid">
            <Content>
                <ShippingForm ShippingModel="@ShippingModel" ShippingForm="@ShippingForm" />
            </Content>
        </WizardStep>
        <WizardStep Label="Confirmation">
            <Content>
                <h2>Registration completed.</h2>
            </Content>
        </WizardStep>
    </WizardSteps>
</TelerikWizard>

@code {
    async Task OnFinishHandler()
    {
        ShowWizard = false;

        await Dialog.AlertAsync("The Registration was submitted successfully", "Done");
    }

    protected override void OnInitialized()
    {
        // Add debugging code to inspect the state of RegisterForm
        Console.WriteLine("MainComponent is being initialized.");
        Console.WriteLine($"RegisterForm is {RegisterForm}");
    }

    public bool? IsRegistrationValid { get; set; }
    public bool? IsShippingValid { get; set; }

    [CascadingParameter]
    public DialogFactory Dialog { get; set; }

    public bool ShowWizard { get; set; } = true;
    public int Value { get; set; }

    public TelerikForm RegisterForm { get; set; } = new TelerikForm();
    public UserPerson UserModel { get; set; } = new UserPerson();

    public TelerikForm ShippingForm { get; set; }
    public ShippingDetails ShippingModel { get; set; } = new ShippingDetails();

    public void OnRegistrationStepChange(WizardStepChangeEventArgs args)
    {

        // Add debugging code to inspect the state of RegisterForm and other variables
        Console.WriteLine("OnRegistrationStepChange is called.");
        Console.WriteLine($"RegisterForm is {RegisterForm}");
        var isFormValid = RegisterForm.IsValid();
        if (!isFormValid)
        {
            IsRegistrationValid = false;
            args.IsCancelled = true;
        }
        else
        {
            IsRegistrationValid = true;
        }
    }

    public void OnShippingStepChange(WizardStepChangeEventArgs args)
    {
        // Add debugging code to inspect the state of ShippingForm and other variables
        Console.WriteLine("OnShippingStepChange is called.");
        Console.WriteLine($"ShippingForm is {ShippingForm}");
        if (Value < args.TargetIndex)
        {
            var isFormValid = ShippingForm.IsValid();
            if (!isFormValid)
            {
                IsShippingValid = false;
                args.IsCancelled = true;
            }
            else
            {
                IsShippingValid = true;
            }
        }
    }
    

    public class UserPerson
    {
        [Required]
        public string FirstName { get; set; } = "John";

        [Required]
        public string LastName { get; set; } = "Smith";

        [Required]
        public string Email { get; set; } = "[email protected]";

        [MinLength(3, ErrorMessage = "The password should be at least 3 characters.")]
        [Required]
        public string Password { get; set; }

        public DateTime? BirthDate { get; set; }

        [Range(typeof(bool), "true", "true", ErrorMessage = "You must agree with the terms.")]
        [Display(Name = "Accept Terms and Conditions")]
        public bool AcceptTerms { get; set; }
    }

    public class ShippingDetails
    {
        [Required]
        public string Country { get; set; }

        [Required]
        public string City { get; set; }

        [Required]
        public string AddressLine { get; set; }

        public string AddressLine2 { get; set; }
    }
}

RegistrationForm.razor

@using static ApplicantTemp.Pages.Wizard.MainComponent;
<!-- RegistrationForm.razor -->
@inherits UserFormBase

<TelerikForm Model="UserModel" @ref="RegisterForm">
    <!-- Registration form content goes here -->
    <FormValidation>
        <DataAnnotationsValidator></DataAnnotationsValidator>
    </FormValidation>
    <FormItems>
        <FormItem LabelText="First Name*:" Field="@nameof(UserModel.FirstName)"></FormItem>
        <FormItem LabelText="Last Name*:" Field="@nameof(UserModel.LastName)"></FormItem>
        <FormItem Field="@nameof(UserModel.Email)">
            <Template>
                <label for="mail" class="k-label k-form-label">Email*:</label>
                <TelerikTextBox Id="mail" @bind-Value="@UserModel.Email" InputMode="email" PlaceHolder="[email protected]"></TelerikTextBox>
                <TelerikValidationMessage For="@(() => UserModel.Email)"></TelerikValidationMessage>
            </Template>
        </FormItem>
        <FormItem Field="@nameof(UserModel.Password)">
            <Template>
                <label for="pass" class="k-label k-form-label">Password*:</label>
                <TelerikTextBox Id="pass" @bind-Value="@UserModel.Password" Password="true"></TelerikTextBox>
                <TelerikValidationMessage For="@(() => UserModel.Password)"></TelerikValidationMessage>
            </Template>
        </FormItem>
        <FormItem Field="@nameof(UserModel.AcceptTerms)" />
    </FormItems>
    <FormButtons></FormButtons>
</TelerikForm>

UserFormBase.razor

@using static ApplicantTemp.Pages.Wizard.MainComponent;
<!-- UserFormBase.razor -->
@inherits ComponentBase

@code {
    [Parameter]
    public UserPerson UserModel { get; set; }

    [Parameter]
    public TelerikForm RegisterForm { get; set; }
}