Blazor Server设置了选择下拉列表的多个默认值

发布于 2025-01-28 16:34:17 字数 738 浏览 2 评论 0原文

我有一个Blazor Server应用程序（.NET 6）页面，其中具有选择的下拉列表，该列表设置为允许多个选择的项目。当页面加载时，我需要设置默认值。如果我只想设置一个选定的值，则此代码正常。但是，如果我想设置多个值，它就不起作用。当我要设置多个值时，如何设置选择列表默认值？这是我所拥有的：

<select value ="@SelectedCities" @onchange="@((ev) => ListChangeEvent(ev, row_id ))" class="form-select" aria-label="Default select example" multiple rows="4"> 
     @foreach (var i in item.values.ToList())
     {
       <option id="@i.Key">@i.Value</option> 
     }
</select>


public string[] SelectedCities { get; set; } = new[] { "New York", "Pittsburgh" };

以上代码不起作用。没有错误，它根本不会选择这两个项目。

但是，如果选择的城市不是一个数组，那么

public string SelectedCities { get; set; } = "New York";

它可以正常工作。

谢谢

原文

I have a Blazor server app (.net 6) page that has a select drop down list, which is set to allow multiple selected items. I need to set default values, when the page loads. If I only want to set one selected value, this code works fine. But, if I want to set multiple values, it does not work. How can I set the select list default values, when there is more than one value I want to set? Here is what I have:

<select value ="@SelectedCities" @onchange="@((ev) => ListChangeEvent(ev, row_id ))" class="form-select" aria-label="Default select example" multiple rows="4"> 
     @foreach (var i in item.values.ToList())
     {
       <option id="@i.Key">@i.Value</option> 
     }
</select>


public string[] SelectedCities { get; set; } = new[] { "New York", "Pittsburgh" };

The above code does not work. There are no errors, it simply does not select the two items.

But, if SelectedCities was not an array, like this:

public string SelectedCities { get; set; } = "New York";

It works fine.

thanks

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以为你会在 2025-02-04 16:34:17


<select multiple @onchange=HandleChange>
    @foreach(var option in Options)
    {
        <option @key=@option selected=@(chosen.Contains(option)) value=@option>@option</option>
    }
</select>

<pre>@string.Join(", ",chosen)</pre>

@code
{
    string[] Options = new string[] {"Abc","Def","Ghi"};
    string[] chosen = new string[] {"Abc","Ghi"};
    void HandleChange(ChangeEventArgs args)
    => chosen = args.Value as string[];
}

demo


<select multiple @onchange=HandleChange>
    @foreach(var option in Options)
    {
        <option @key=@option selected=@(chosen.Contains(option)) value=@option>@option</option>
    }
</select>

<pre>@string.Join(", ",chosen)</pre>

@code
{
    string[] Options = new string[] {"Abc","Def","Ghi"};
    string[] chosen = new string[] {"Abc","Ghi"};
    void HandleChange(ChangeEventArgs args)
    => chosen = args.Value as string[];
}

Demo

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べ映画 2025-02-04 16:34:17

在Blazor 6（或更高）中，您不再需要手动执行此操作。您可以直接绑定收集（尽管您仍然需要将其转换为数组）。

Enum example:

<select @bind="MyArray" multiple>
    @foreach (var item in (MyEnum[])Enum.GetValues(typeof(MyEnum)))
    {
        <option value="@item" @key="item">@item.Humanize()</option>
    }
</select>

In Blazor 6 (or higher), you no longer need to manually do this. You can bind your collection directly (though you still need to convert it to an array).

Enum example:

<select @bind="MyArray" multiple>
    @foreach (var item in (MyEnum[])Enum.GetValues(typeof(MyEnum)))
    {
        <option value="@item" @key="item">@item.Humanize()</option>
    }
</select>

https://learn.microsoft.com/en-us/aspnet/core/blazor/components/data-binding?view=aspnetcore-6.0#multiple-option-selection-with-select-elements

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~没有更多了~