AspNetCore.Docs/aspnetcore/blazor/includes/state-container.md

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Nested components typically bind data using *chained bind* as described in <xref:blazor/components/data-binding>. Nested and un-nested components can share access to data using a registered in-memory state container. A custom state container class can use an assignable <xref:System.Action> to notify components in different parts of the app of state changes. In the following example:

* A pair of components uses a state container to track a property.
* One component in the following example is nested in the other component, but nesting isn't required for this approach to work.

`StateContainer.cs`:

```csharp
using System;

public class StateContainer
{
    private string savedString;

    public string Property
    {
        get => savedString;
        set
        {
            savedString = value;
            NotifyStateChanged();
        }
    }

    public event Action OnChange;

    private void NotifyStateChanged() => OnChange?.Invoke();
}
```

In `Program.Main` (Blazor WebAssembly):

```csharp
builder.Services.AddSingleton<StateContainer>();
```

In `Startup.ConfigureServices` (Blazor Server):

```csharp
services.AddScoped<StateContainer>();
```

`Shared/Nested.razor`:

```razor
@inject StateContainer StateContainer
@implements IDisposable

<h2>Nested component</h2>

<p>Nested component Property: <b>@StateContainer.Property</b></p>

<p>
    <button @onclick="ChangePropertyValue">
        Change the Property from the Nested component
    </button>
</p>

@code {
    protected override void OnInitialized()
    {
        StateContainer.OnChange += StateHasChanged;
    }

    private void ChangePropertyValue()
    {
        StateContainer.Property = 
            $"New value set in the Nested component: {DateTime.Now}";
    }

    public void Dispose()
    {
        StateContainer.OnChange -= StateHasChanged;
    }
}
```

`Pages/StateContainer.razor`:

```razor
@page "/state-container"
@inject StateContainer StateContainer
@implements IDisposable

<h1>State Container component</h1>

<p>State Container component Property: <b>@StateContainer.Property</b></p>

<p>
    <button @onclick="ChangePropertyValue">
        Change the Property from the State Container component
    </button>
</p>

<Nested />

@code {
    protected override void OnInitialized()
    {
        StateContainer.OnChange += StateHasChanged;
    }

    private void ChangePropertyValue()
    {
        StateContainer.Property = 
            $"New value set in the State Container component: {DateTime.Now}";
    }

    public void Dispose()
    {
        StateContainer.OnChange -= StateHasChanged;
    }
}
```

The preceding components implement <xref:System.IDisposable>, and the `OnChange` delegates are unsubscribed in the `Dispose` methods, which are called by the framework when the components are disposed. For more information, see <xref:blazor/components/lifecycle#component-disposal-with-idisposable>.