Blazor two-way binding on a child component with a default value

Question

Given a Child component:

<p>Name: @Name</p>

@code {
    [Parameter]
    public string Name { get; set; } = "Scooby Do";
    [Parameter]
    public EventCallback<string> NameChanged { get; set; }
}

And a Parent component with two-way binding on the Name property:

Name: <InputText @bind-Value=@Name/>
<ChildComponent @bind-Name=@Name />

@code {
    public string Name { get; set; }
}

It appears the ChildComponent.Name is overwritten by the null value from the ParentComponent.Name property.

I would like the value "Scooby Do" from the Child to be bound up to the Parent as the default value.

How do I enable the two-way binding but use the Child component's default values?

Answer 1

To apply the default rule once, add this to the Child:

[Parameter]
public string Name { get; set; } // = "Scooby Do";  
... 

protected override async Task  OnInitializedAsync()
{
    if (string.IsNullOrEmpty(Name) )
    {
        await NameChanged.InvokeAsync("Scooby Do");
    }
}

when you want to replace it with "Scooby Do" again when the user empties the textbox then override OnParametersSetAsync instead, with the same code.