In WPF Prism, screen navigation happens through a feature called Region.

For navigation-based screen transitions (where the Region part that makes up part of the screen switches), you implement the **INavigationAware** interface on the destination.

The **`IsNavigationTarget` method** that this generates decides, via its bool return value, whether to reuse the ViewModel instance — but **even returning `false` doesn't release the memory**.

**【Return value of IsNavigationTarget】**  
- true: Reuse the instance. The constructor isn't called the next time the screen is launched.
- false: Don't reuse the instance. The constructor is called the next time the screen is launched. However, **the memory is not released**.

## How to release memory on navigation-based screen transitions

Implement the **IRegionMemberLifetime interface** on the ViewModel, and set the **KeepAlive property to false**.

Also, if you're implementing the **INavigationAware interface** alongside it, set **IsNavigationTarget to True**.

Here's an example implementation on a ViewModel.

▼SampleViewModel.cs
```cs
public class SampleViewModel : BindableBase, INavigationAware, IRegionMemberLifetime
{
    /// <summary>
    /// ViewModel破棄に伴いメモリ開放する際はfalse
    /// </summary>
    public bool KeepAlive { get; set; } = false;

    public SampleViewModel()
    {
    }

    public bool IsNavigationTarget(NavigationContext navigationContext)
    {
        //// RegionMemberLifetime(KeepAlive = false)でViewModelを破棄するため、こちらはTrue
        return true;
    }

    public virtual void OnNavigatedFrom(NavigationContext navigationContext)
    {
    }

    public virtual void OnNavigatedTo(NavigationContext navigationContext)
    {
    }
}
```

That's it.