Xamarin.forms 列表视图项目源未更新

Question

I am having a problem with my xamarin.forms list view. I have created a list view that has an items source that is binded to a List of a custom class. In the app.xaml.cs, I have the exact same list. In another form, I am updating the list that resides in app.xaml.cs. When the first form with the list view is brought back up, on appearing I set the local list that is binded to the list in app.xaml.cs. But, the items in the list view UI dont update. Can someone please help me with this?

MainPage.xaml (with list view):

`

<?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="TrackExpensesApp.MainPage">

        <ContentPage.ToolbarItems>
            <ToolbarItem Text="+"
                        Clicked="OnAddExpenseClicked" />
        </ContentPage.ToolbarItems>

        

    <ListView x:Name="ExpenseEntriesListView"
                        ItemsSource="{Binding ExpenseEntries}"
                        SelectionMode="Single"
                        ItemSelected="ExpenseEntriesItemSelected">
        <ListView.ItemTemplate>
            <DataTemplate>
                <Grid Padding="10"
                                RowDefinitions="Auto, *"
                                ColumnDefinitions="Auto, *">
                    <Label Grid.ColumnSpan="2"
                                    Text="{Binding Name}"
                                    VerticalOptions="End" />
                    <Label Grid.Row="1"
                                    Text="{Binding DateCreated}"
                                    VerticalOptions="End" />
                    <Label Grid.Row="1"
                                    Grid.Column="1"
                                    Text="{Binding Category}"
                                    VerticalOptions="End" />
                </Grid>
            </DataTemplate>
        </ListView.ItemTemplate>
    </ListView>
</ContentPage>

` MainPage.xaml.cs (with list view):

`

public partial class MainPage : ContentPage
    {
        public IList<ExpenseEntry> ExpenseEntries { get; set; }

        public MainPage()
        {
            InitializeComponent();
        }

        async void OnAddExpenseClicked(object sender, EventArgs e)
        {
            await Navigation.PushAsync(new ExpensesEntryPage());
        }

        protected override void OnAppearing()
        {
            ExpenseEntries = (Application.Current as TrackExpensesApp.App).ExpenseEntries;
            
            BindingContext = this;
        }

        async void ExpenseEntriesItemSelected(object sender, SelectedItemChangedEventArgs e)
        {
            ExpenseEntry selectedItem = e.SelectedItem as ExpenseEntry;

            await Navigation.PushAsync(new ExpensePage());
        }
    }

`

App.xaml.cs:

`

public partial class App : Application
    {
        public IList<ExpenseEntry> ExpenseEntries { get; set; }
        public IList<string> Categories { get; set; }

        public App()
        {
            InitializeComponent();

            // Load in all expenses before loading in the main page
            ExpenseEntries = new List<ExpenseEntry>();

            Categories = new List<string>();
            Categories.Add("Monthly");
            Categories.Add("Vacation");
            Categories.Add("Other");

            MainPage = new NavigationPage(new MainPage());

            BindingContext = this;
        }

        protected override void OnStart()
        {
        }

        protected override void OnSleep()
        {
        }

        protected override void OnResume()
        {
        }
    }

` I would truly appreciate it if someone would get back to me as soon as possible. Thank you!

Answer 1

We need to call OnPropertyChanged in setter method to notify that a change happened on a property,so that the UI would change after then.

MainPage

Change your code as below

private IList<string> expenseEntries;
public IList<string> ExpenseEntries { 
  get
  {
      return expenseEntries;
  }
  set 
  {
      expenseEntries = value;
      OnPropertyChanged();  //add this line
  } 
}