Blazor (Server-side) communicate between sibling components

Scenario

Let's suppose:

<CRUD>
    <GRID/>
    <FORM/>
</CRUD>

Option 1: Delegate

Using a delegate, you can capture the reference for GRID component and call a GRID method from FORM through a delegate. Try delegate sample at blazorfiddle.

Simplifying:

On CRUD:

<GRID @ref="mygrid" />
<FORM mydelegate="@( (s) => mygrid.setData(s) )" />

@code
{
    protected GRID mygrid;
}

On GRID:

<h1>@data</h1>

@code
{
    string data;

    public void setData(string value)
    {
        data = value;
        StateHasChanged();
    }
}

On FORM:

<input @bind-value=@somedata />
<button @onclick="@( () => mydelegate(somedata ?? "hi") )">press</button>

@code
{
    [Parameter] public Action<string> mydelegate {set; get;}
    string somedata;
}

Option 2: Sharing the list

Just share your list between components. You cal also subscribe GRID to add event list. More info at How to handle add to list event?. Of course, you can use also an ObservableCollection. Maybe you can avoid event, just adding to list and call StateHasChanged may be enough.

Remember you can share the list via parameters or cascade parameter.

<CRUD>
    <GRID data=@mylist />
    <FORM data=@mylist />
</CRUD>

Other options.

Do you have several more options like using a singleton via Dependency Injection, eventcallback, ... . I suggest to you to read 3 Ways to Communicate Between Components in Blazor by @Chris Sainty

You should have posted a minimal repo with your question so that we can clearly see the issue you're facing.

However, generally speaking, there are a couple of ways to do this. In one of my answers in the Blazor section I have described three ways how to enable such scenario.

In this answer I'll suggest you to employ the App State Pattern, from which you can manage the state of your components, perform CRUD Actions related to the data in your components, refresh the components, etc.

An excellent sample created by Steve Anderson, which employ the App State Pattern is FlightFinder. This sample (Client project) defines a service named AppState which is injected to a number of components, and provide them with various functionalities. Please, inspect this class, and the components involved, and how they communicate with each other, and apply what you'll learn in your app. Don't hesitate to ask any question.

Note: If you are not acquainted with this sample, learn it thoroughly as this is an excellent way to learn Blazor.

See my answers here and here.

Hope this helps...