Blazor -- access global variables from layout component

Suppose you've created a Company parent component which can get a route parameter to represent a company ID, the value of which is used to retrieve the company's details that may be displayed in a child component. You may define the parent component like this:

Company.razor

@page "/company"
@page "/company/{ID}"

@code {
    [Parameter]
    public string ID { get; set; }
}

Note: The two route templates above are necessary...

Answering your question... Add this code to the MainLayout component

@code{

    public string ID { get; set; }

    protected override void OnParametersSet()
    {
        // pull out the "ID" parameter from the route data
        object id = null;
        if ((this.Body.Target as RouteView)?.RouteData.RouteValues?.TryGetValue("ID", out id) == true)
        {
            ID = id?.ToString();
        }

    }
}

Note: The code above extricates the value of the ID parameter from the RouteData, and stores it in the ID property. Now you can do with it, whatever you want... including passing it to the the NavMenu Component if it's necessary there. This is how you can do it:

Add a Component Parameter property to the NavMenu Component, like this:

[Parameter]
public string ID { get; set; }

And add an ID component parameter attribute to the NavMenu component instance (located at the top of the MainLayout component. It should be now <NavMenu ID="@ID"/>

Note: This code sample describes how you can extricate the parameter ID (AccountID, etc.) within MainLayout and how to pass it to its child component, NavMenu ( TopNav, LeftNav). Now that you've got the ID, you can pass it to any data store you've defined, and retrieve some data details...

Hope this helps...

1. Create a service getting and setting the current account.
2. Bind the NavBar on this service current account properties