Xamarin.Forms block UI when ItemsSource load a big data - visual-studio

Question

I do not load a small data from the API, in C# code, they are loaded in advance and everything seems to be fine, but as soon as I open the page where ItemsSource = "{Binding BigData}", my UI is blocked for 10 seconds.
Are there any ideas to open the page first, then start loading data without blocking the UI?

Answer 1

I would to suggest you can kick off a task in your view models constructor that loads the data. Using Async and await to load bid data.
I do one sample that using ListView to display 100000 records.
<StackLayout>
<Label Text="test ui in xamarin.forms asyn" />
<ActivityIndicator IsRunning="{Binding isBusy}" IsVisible="{Binding isBusy}" />
<ListView x:Name="listview1" ItemsSource="{Binding Items}">
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<StackLayout Orientation="Horizontal">
<Label Text="{Binding name}" />
<Label HorizontalOptions="CenterAndExpand" Text="{Binding age}" />
</StackLayout>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
</StackLayout>
public partial class Page19 : ContentPage
{
public Page19()
{
InitializeComponent();
this.BindingContext = new ItemsViewModel();
}
}
public class ItemsViewModel:ViewModelBase
{
private bool _isBusy;
public bool isBusy
{
get { return _isBusy; }
set
{
_isBusy = value;
RaisePropertyChanged("isBusy");
}
}
public ObservableCollection<people> Items { get; set; }
public ItemsViewModel()
{
Items = new ObservableCollection<people>();
isBusy = true;
Task.Run(async () => await LoadItems());
}
public async Task LoadItems()
{
var items = new ObservableCollection<people>(); // new collection
if (isBusy)
{
await Task.Delay(10000);
// var loadedItems = ItemsService.LoadItemsDirectory();
//foreach (var item in loadedItems)
// items.Add(item);
for (int i = 0; i < 100000; i++)
{
people p = new people();
p.name = "people " + i;
p.age = i;
items.Add(p); // items are added to the new collection
}
Items = items; // swap the collection for the new one
RaisePropertyChanged(nameof(Items)); // raise a property change in whatever way is right for your VM
isBusy = false;
}
}
}
public class people
{
public string name { get; set; }
public int age { get; set; }
}
ViewModelBase is one class that implementing INotifyPropertyChanged
public class ViewModelBase : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
public void RaisePropertyChanged(string propertyName)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(propertyName));
}
}
}