Detecting whether page is navigated to or off C#-CodePudding

In my WPF application i have multiple pages. One page is called "startup" and this is the one shown most of the time. An NFC-Reader is running in the background on a thread and everytime you scan a card, it executes code.

My navigation works by having a class called "InstanceContainer.cs" which basically just holds all the instances to my pages which i then navigate to using (for example) NavigationService.Navigate(InstanceContainer.startup());

However i want it to only execute said code, when "startup" is shown while a card is scanned. My idea would be to just set a public bool like public bool startupShown; inside of "startup" which is then checked for in the thread that runs the NFC-Scanning. But how do i neatly update this bool? Of course it could be updated manually on every buttonclick that leads away and to "startup", but there has to be a better way than that.

I found this but didn't quite understand it nor could i get it to work. Thanks in advance

CodePudding user response：

You could use the Page's IsLoaded property to determine whether it's currently loaded and displayed in the Frame.

This property can however not be accessed directly from a background thread so you could either add your own field or property to the start page and handle the Loaded and Unloaded events to set it...:

public partial class StartupPage : Page
{
    public bool startupShown;

    public Page1()
    {
        InitializeComponent();
        Loaded  = (s, e) => startupShown = true;
        Unloaded  = (s, e) => startupShown = false;
    }
}

...or use the dispatcher to access the built-in Loaded property from the background thread:

Page page = InstanceContainer.startup();
bool isloaded = page.Dispatcher.Invoke(() => page.IsLoaded);