Blazor 双向绑定搜索栏出现错误消息“对象引用未设置为对象的实例”——我是否错误地处理了模型？

Question

我写了以下代码，在传递字符串时效果很好

<MudTextField @bind-Value="@searchTerm" Placeholder="Sök" />

@foreach (var item in filteredItems)
{
    <p>@item</p>
}

@code {
    private string searchTerm = "";
    private List<string> items = new List<string> {
        "1","2","3"
    };

    private IEnumerable<string> filteredItems =>
        items.Where(i => i.ToLower().Contains(searchTerm.ToLower()));
}

然后我更改了代码，但通过了一个模型练习，但是那个 dosen 工作

我在控制台上给我以下错误。

Microsoft.AspNetCore.Components.WebAssembly.Rendering.WebAssemblyRenderer[100] 未处理的异常呈现组件：对象引用未设置到对象的实例。 System.NullReferenceException：对象引用未设置到对象的实例。 在

<MudTextField @bind-Value="@searchTerm" Placeholder="Sök" />

@foreach (var item in filteredItems)
{
    <p>@item.Title</p>
}

@code {
    private string searchTerm = "";
    private List<Exercise> items = new List<Exercise> {
        new Exercise
        {
            Id = 1,
            Title = "Push-ups",
            Instructions = new Dictionary<int, string>()
            {
                { 1, "Get into a plank position with your hands slightly wider than shoulder-width apart." },
                { 2, "Lower your body until your chest nearly touches the floor." },
                { 3, "Push your body back up to the starting position, keeping your elbows close to your body." }
            }
        },
        new Exercise
        {
            Id = 2,
            Title = "Squats",
            Instructions = new Dictionary<int, string>()
            {
                { 1, "Stand with your feet shoulder-width apart." },
                { 2, "Lower your body as if you are sitting back into a chair." },
                { 3, "Keep your knees over your ankles and your weight in your heels." },
                { 4, "Push back up to the starting position." }
            }
        },
        new Exercise
        {
            Id = 3,
        }
    };

    private IEnumerable<Exercise> filteredItems =>
        items.Where(i => i.Title.ToLower().Contains(searchTerm.ToLower()));
}

有人知道为什么吗？起初我厌倦了使用我的 IExerciseDataStore 来获取我的练习，但我一遍又一遍地遇到同样的问题。

@inject IExerciseDataStore<Exercise> exerciseDataStore
...

protected override async Task OnInitializedAsync()
{
    await base.OnInitializedAsync();

    items = await exerciseDataStore.GetAllExercisesAsync();
}

Answer 1

使用 MudBlazor 时正确制定了 Binding，doc 阅读更多。 总之：@bind-Value="SearchTerm" 也会在“后台”绑定 ValueChanged="SearchTerm"。

我遇到的问题是@Axekan 在我不断收到 NullReferenceExccption 的评论中写的，因为加载页面时我拥有的数据为空。

         ...
            new Exercise
            {
               Id = 3,
            }

Title 或 Instruction 等属性未设置并且将为 null，因为 Title - string，Instructions - Dictionary 这些是引用类型，如果未设置将在模型（练习）初始化时指向 null。

改为：为了解决空引用，我加载了页面。

         ...
            new Exercise
            {
               Id = 3,
               Title = String.Empty,
               Instructions = new Dictornary<int,string>()
            }