onChange event not firing Blazor InputSelect

问题

I have the following Code for an InputSelect

               <InputSelect class="form-control form-control form-control-sm"
                             placeholder="Role"
                             disabled="@IsReadOnly"
                             @bind-Value="Model.Role"
                              @onchange="@RoleChanged">
                    <option value="Member">Member</option>
                    <option value="Admin">Admin</option>
                    <option value="Pioner">Pioneer</option>
                    <option value="Retailer">Retailer</option>
                </InputSelect>

And for the Code:

bool ShowCreated;
bool ShowUpdated;
bool IsReadOnly;
string SelectedRole;

public EditForm AccountForm;
public Multi.Dtos.RegistrationDto Model = new Dtos.RegistrationDto() { Role = "Member" };

public void RoleChanged(ChangeEventArgs e)
{
    SelectedRole = e.Value.ToString();
    Console.WriteLine(e.Value);
}

The RoleChange function is not invoked when i try to select a new item. Can someone point out what wrong with this. The value of the proper has changed but the Event was not called.

回答1:

Note:

InputSelect is a component element, not HTML element, which is why you cannot apply to it the @onchange compiler directive. This directive is applied to elements, usually but not necessarily with the value attribute to form the so- called two way data-binding.
@bind-Value is a compiler directive directive instructing the compiler to produce code that enable two-way data binding between components. Applying @bind-Value to the InputSelect component requires you (already done in this case by the Blazor team) to define a parameter property named Value and an EventCallback 'delegate', conventionally named ValueChanged. Value and ValueChanged are properties of the InputSelect component.

There are a couple of ways to do this:

 <InputSelect ValueExpression="@(()=>comment.Country)" 
                                           Value="@comment.Country" 
                 ValueChanged="@((string value) => OnValueChanged(value ))">
        <option value="">Select country...</option>
        <option value="USA">USA</option>
        <option value="Britain">Britain</option>
        <option value="Germany">Germany</option>
        <option value="Israel">Israel</option>
 </InputSelect>

And

 private Task OnValueChanged(string value)
{
    // Assign the selected value to the Model 
    comment.Country = value;
   return Task.CompletedTask;
}

You can also implement INotifyPropertyChanged.PropertyChanged Event in your Model, as dani herrera has suggested. You do that if you want to do away with the Forms components, including the EditForm, and use the normal HTML tags instead, in which case you'll be able to do something like:

<input type="text" value="@MyValue" @onchange=OnChange"/>

Of course your model class is going to be thick, and it should communicate with the EditContext....

Hope this helps...

来源：https://stackoverflow.com/questions/61756167/onchange-event-not-firing-blazor-inputselect

标签

asp.net-core

blazor

blazor-server-side