Xamarin-在iOS上显示数据的ListView

Question

My list views data displays correctly on UWP and Android but not for IOS. I think it has something to do with the OnAppearing method I'm using and when it actually gets called on IOS.

From my Dashboard when I navigate to an Item list page I have the following code behind on the ItemPage

public ItemPage(string category = null, bool fromDashboard = false)
{
    InitializeComponent();
    BindingContext = new ItemViewModel(category, fromDashboard);
}

protected override void OnAppearing()
{
    var vm = BindingContext as ItemViewModel;
    vm?.GetData();
    base.OnAppearing();
}

Then in my ItemViewModel class I have a constructor that accepts a category and fromDashboard flag and sets some properties.

The ItemViewModel GetData() call is as follows:

public void GetData()
{
    this.Items = this.RefreshData(this.ItemService.GetAll(this.SelectedCategory));

    if (this.FromDashboard)
        this.Items = this.Items.Where(x => x.Status != "Complete").ToObservableCollection();
}

And then finally the ItemPage.xaml has a ListView with the ItemsSource="{Binding Items}"

For some reason this works fine on Windows and Android but no data will show on IOS. Is the page being rendered before the OnAppearing method or something?

Answer 1

When editing values of ViewModel properties in the code, you have to call OnPropertyChanged method (from INotifyPropertyChanged interface) to let the UI know it has to update.

Like so:

public void GetData()
{
    this.Items = this.RefreshData(this.ItemService.GetAll(this.SelectedCategory));

    if (this.FromDashboard)
        this.Items = this.Items.Where(x => x.Status != "Complete").ToObservableCollection();

    OnPropertyChanged(nameof(this.Items));
}