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异步更新属性

blazor .net c#

vernou · 技术社区 · 7 年前

Todo.cshtml:

@page "/todo"

<h1>Todo (@todos.Count(todo => !todo.IsDone))</h1>

<ul>
    @foreach (var todo in todos)
    {
        <li>
            <input type="checkbox" bind="@todo.IsDone" />
            <input bind="@todo.Title" />
        </li>
    }
</ul>

<input placeholder="Something todo" bind="@newTodo"/>
<button onclick="@AddTodo">Add todo</button>

@functions {
    IList<TodoItem> todos = new List<TodoItem>();


    string newTodo;
    void AddTodo()
    {
        if (!string.IsNullOrWhiteSpace(newTodo))
        {
            todos.Add(new TodoItem { Title = newTodo });
            newTodo = string.Empty;
        }
    }
}

public class TodoItem
{
    private bool _isDone;

    public string Title { get; set; }
    public bool IsDone
    {
        get => _isDone;
        set
        {
            _isDone = value;
            Task.Run(() =>
            {
                //Simulate work
                System.Threading.Thread.Sleep(TimeSpan.FromSeconds(2));
                //Update property
                Title = Title + " - Done";
            });
        }
    }
}

我需要解释要更新的UI StateHasChanged() : https://github.com/aspnet/Blazor/issues/1413

但我不能在TodoItem中调用此方法(我不想让TodoItem知道Blazor组件)。

您有更新UI的解决方案吗?

2 回复 | 直到 7 年前

Ruben Helsloot Rez 5 年前

您应该执行以下操作:

```
 public event Action OnChange;
```
在这个类中定义一个方法 NotifyStateChanged()
```
 private void NotifyStateChanged() => OnChange?.Invoke();
```
此方法触发 OnChange

在todo组件中,添加 StateHasChanged 方法中使用的事件委托 TodoItem 因此,类:

 @functions
 {
     protected override void OnInit()
     {
         state.OnChange += StateHasChanged;
     }
 }

dani herrera 7 年前

简单的答案是 StateHasChanged(); “修改您的变量后” :

        Task.Run(() =>
        {
            //Simulate work
            System.Threading.Thread.Sleep(TimeSpan.FromSeconds(2));
            //Update property
            Title = Title + " - Done";
            StateHasChanged();
        });

由于您的方法是异步的,请重写为:

        Task.Run(async () =>  //<--here async
        {
            //Simulate async work
            Task.Run( async () => {
                await Task.Run( () => {} ); //<--- await
                System.Threading.Thread.Sleep(TimeSpan.FromSeconds(2));
            });
            //Update property
            Title = Title + " - Done";
            StateHasChanged();
        });

为了避免反模式和编写干净的代码,您的ModelView可能会有一个公共事件来通知UI它已更改,只需将UI上的此事件连接到 StateHasChanged();

我在这里写下Blazor计数器示例,它被修改为:

@page "/counter"

<h1>Counter</h1>

<p>Current count: @currentCount</p>

<button class="btn btn-primary" onclick="@IncrementCount">
    Click me @s <!-- here var -->
</button>

@functions {
    int currentCount = 0;

    string s = "";

    void IncrementCount()
    {
        currentCount++;
        Task.Run(() =>
            {
                //Simulate work
                Task.Run( async () => {
                    await Task.Run( () => {} );
                    System.Threading.Thread.Sleep(TimeSpan.FromSeconds(2));}
                        );
                //Update property
                s = s + " - Done";
                StateHasChanged();
            });
        }
    }
}

编辑

呼叫 StateHasChanged

    Task.Run(() =>
    {
        //Simulate work
        System.Threading.Thread.Sleep(TimeSpan.FromSeconds(2));
        //Update property
        Title = Title + " - Done";
        StateHasChanged();
    });

通过

    Invoke( () =>
    {
       ...