Blazor onchange event with select dropdown

debugcn 投稿 Dev

Grand Masta1 :

So I have been stuck trying to get a simple onchange to fire when a select dropdown value changes. Like so:

<select class="form-control d-flex" onchange="(dostuff())">
    @foreach (var template in templatestate.templates)
    {
        <option [email protected]>@template.Name</option>
    }
</select>

with the method being called:

void dostuff()
{
   Console.WriteLine("first spot is firing");
    _template = templatestate.templates.FirstOrDefault(x => x.Name == 
    _template.Name);
    Console.WriteLine("second spot is firing");
}

The result I get it no matter how I try to reorient it is this error in the browser.

Uncaught Error: System.ArgumentException: There is no event handler with ID 0

Is there something obvious and key that I am missing? Because I have a button onclick event that works just fine in the same page.

Patrick Knott :

Your answer should be in the cshtml:

<select onchange=@DoStuff>
    @foreach (var template in templates)
    {
        <option value=@template>@template</option>
    }
</select>

Then your @functions (in razor components @code instead. See: https://docs.microsoft.com/vi-vn/aspnet/core/mvc/views/razor?view=aspnetcore-3.0#functions) should look like:

@functions {
    List<string> templates = new List<string>() { "Maui", "Hawaii", "Niihau", "Kauai", "Kahoolawe" };
    string selectedString = "Maui";

    void DoStuff(ChangeEventArgs e)
    {
        selectedString = e.Value.ToString();
        Console.WriteLine("It is definitely: " + selectedString);
    }
}

You could also just use a bind...

<select bind="@selectedString">

but onchange=:@DoStuff allows you to perform logic on selection.

Note that in Preview 6, it appears that syntax will be @onchange="@DoStuff" with the future promising @onchange="DoStuff". Here's a link to some changes: Blazor Preview 6

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