Blazor server side pass an object instance as parameter to nested component

There are several ways to do multi-component two way communications.

You can create a notification service and subscribe components to notifications - here's a question and answer that shows you how to do that How can I trigger/refresh my main .RAZOR page from all of its sub-components within that main .RAZOR page when an API call is complete?.

Here is how to do it with a cascaded context object with notifications - similar in many ways to EditContext.

First the context object. We don't mix delegates and events with our data objects, so we create a specific object for the purpose that contains our edit model and it's associated events.

Here's PersonEditContext:

public class PersonEditContext
{
    public Person Person { get; set; } = new();
    public Action? Updated { get; set; }

    public void NotifyUpdated()
        => this.Updated?.Invoke();
}

Next ComponentA.

It:

1. Picks up the cascaded context and create an EditContext from the Person instance.
2. Wires up a handler to the edit context's OnFieldChanged event which raises the Action in the PersonEditContext cascaded instance.
3. Wires up a handler to the PersonEditContext cascaded instance Updated Action to trigger a render event on the component.
4. Implements IDisposable to tear down the handler wiring.
5. itsMe prevents a render event if the component itself raises the event.

@implements IDisposable

<h3>ComponentA</h3>
<div>@personContext.Person.FirstName</div>
<div>@personContext.Person.LastName</div>
<p></p>
<hr />

<EditForm EditContext=this.editContext OnValidSubmit=HandleValidSubmit>
    <!-- Input2 -->
    <InputText id="name" @bind-Value="personContext.Person.FirstName" />
</EditForm>

@code {
    private EditContext? editContext;
    private bool itsMe;
    private Person person => personContext.Person;
    [CascadingParameter] private PersonEditContext personContext { get; set; } = new();

    protected override void OnInitialized()
    {
        editContext = new EditContext(person);
        editContext.OnFieldChanged += OnFieldChanged;
        personContext.Updated += Updated;
        base.OnInitialized();
    }

    private void HandleValidSubmit()
    {
    }

    private void OnFieldChanged(object? sender, FieldChangedEventArgs e)
    {
        itsMe = true;
        personContext.NotifyUpdated();
    }

    private void Updated()
    {
        if (!itsMe)
            StateHasChanged();

        itsMe = false;
    }

    public void Dispose()
    {
        if (editContext is not null)
            editContext.OnFieldChanged -= OnFieldChanged;

        if (personContext is not null)
            personContext.Updated -= Updated;
    }
}

And MyPage which is very similar:

@page "/"
@implements IDisposable

<EditForm EditContext=this.editContext OnValidSubmit=HandleValidSubmit>
    <InputText id="name" @bind-Value="person.FirstName" />
</EditForm>

<CascadingValue Value="personContext" IsFixed="true">
    <ComponentA />
    <ComponentB />
</CascadingValue>

@code {
    private EditContext? editContext;
    private PersonEditContext? personContext;
    private Person person => personContext?.Person ?? new();
    private bool itsMe;

    protected override void OnInitialized()
    {
        personContext = new PersonEditContext { Person = new Person { FirstName = "Nancy", LastName = "Dvolio" } };
        editContext = new EditContext(person);
        editContext.OnFieldChanged += OnFieldChanged;
        personContext.Updated += Updated;
    }

    private void HandleValidSubmit()
    {
        // Whatever
    }

    private void OnFieldChanged(object? sender, FieldChangedEventArgs e)
    {
        itsMe = true;
        personContext?.NotifyUpdated();
    }

    private void Updated()
    {
        if (!itsMe)
            StateHasChanged();

        itsMe = false;
    }

    public void Dispose()
    {
        if (editContext is not null)
            editContext.OnFieldChanged -= OnFieldChanged;

        if (personContext is not null)
            personContext.Updated -= Updated;
    }
}

Here's ComponentB to demonstrate the multi-component behaviour:

@implements IDisposable
<div class="bg-primary text-white p-2 m-2" >
    <h3>ComponentB</h3>
    <div>@person.FirstName</div>
    <div>@person.LastName</div>
</div>

@code {
    private Person person => personContext.Person;
    [CascadingParameter] private PersonEditContext personContext { get; set; } = new();

    protected override void OnInitialized()
    {
        personContext.Updated += Updated;
        base.OnInitialized();
    }

    private void Updated()
    {
        StateHasChanged();
    }

    public void Dispose()
    {
        if (personContext is not null)
            personContext.Updated -= Updated;
    }
}