How to access a ListView from another page?(Xamarin Forms)

Question

I would like to modify the content of a list View from my MainPage. The list view is in another page called LoadResultsPage. Here is the button in the main page which calls the function:

<Button Text="Load Results" Clicked="FetchData"></Button>

Here is the function which is called:

public async void FetchData(object sender, System.EventArgs e)
    {
        /* string apiUrl = null;
         if (Device.RuntimePlatform == Device.Android)
             apiUrl = "https://10.0.2.2:5001/api";
         else if (Device.RuntimePlatform == Device.iOS)
             apiUrl = "https://localhost:5001/api";
         else
             throw new Exception();*/
        await Navigation.PushAsync(new LoadResultsPage());
        var httpClient = new HttpClient();
        var response = await httpClient.GetStringAsync("http://localhost:5001/api/Calcs");
        var login = JsonConvert.DeserializeObject<List<Calc>>(response);
        Lista.ItemsSource = login;
    }

Here Lista(at the bottom of the function) is not recognized and the error is : "The name 'Lista' does not exist in the current context"

And finally here is the content of the page LoadResultsPage where the list view that i want to modify is:

<?xml version="1.0" encoding="utf-8" ?>
  <ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
         xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
         x:Class="Calculator.Views.LoadResultsPage">
<Grid  VerticalOptions="FillAndExpand">
    <ListView x:Name="Lista" >
        <ListView.ItemTemplate>
            <DataTemplate>
                <ViewCell >
                    <StackLayout >
                        <Label Text="{Binding Id}" TextColor="Black"></Label>
                        <Label Text="{Binding Value}"></Label>
                    </StackLayout>
                </ViewCell>
            </DataTemplate>
        </ListView.ItemTemplate>
    </ListView>
</Grid>

How do i populate the two labels with the info in the variable "login"?

Answer 1

Please kindly read about MVVM that might change your concept globally. It is considered not a best style to access ui elements between pages.

Anyway directly answering your question use some static model to exchange data globally inside app.

    public class Exchange
    {
        private static Exchange _instance;
        public static Exchange Data
        {
            get
            {
                if (_instance == null)
                {
                    _instance = new Exchange();
                }
                return _instance;
            }
        }

        public string Buffer { get; set; }

        public ListView MyListView { get; set; }

    }

Example: Exchange.Data.Buffer will be accessible from anywhere.

For your ListView in its page constuctor after the InitializeComponent(); set

Exchange.Data.MyListView = this;

Now the important part that if you access your ListView from another page you have to do it on UI thread. Example:

        Device.BeginInvokeOnMainThread(() =>
        {
            // Update the UI
            Exchange.Data.MyListView.ItemsSource = whatever;
        });