I have read samples on the internet and some are very hard to learn.
I want to learn how to understand when the ListView is scrolling down and if more data is still available, how I can get the data from the internet while showing a ProgressRing on screen.
For my example, I use JSON to get data from a PHP server, and every request I get 10 items from the database.
If you could please provide an easy to understand sample, it would be very much appreciated.
public sealed partial class MainPage : Page
{
public MainPage()
{
this.InitializeComponent();
myListView.ItemsSource = new ItemsDataSource();
}
}
public interface IIncrementalSource<T>
{
Task<IEnumerable<T>> GetPagedItems(int pageIndex, int pageSize,string url);
}
public class IncrementalLoadingCollection<T, I> : ObservableCollection<I>,
ISupportIncrementalLoading
where T : IIncrementalSource<I>, new()
{
private T source;
private int itemsPerPage;
private bool hasMoreItems;
private int currentPage=0;
string url;
public IncrementalLoadingCollection(string url,int itemsPerPage = 10)
{
this.source = new T();
this.itemsPerPage = itemsPerPage;
this.hasMoreItems = true;
this.url = url;
}
public bool HasMoreItems
{
get { return hasMoreItems; }
}
public IAsyncOperation<LoadMoreItemsResult> LoadMoreItemsAsync(uint count)
{
var dispatcher = Window.Current.Dispatcher;
return Task.Run<LoadMoreItemsResult>(
async () =>
{
uint resultCount = 0;
var result = await source.GetPagedItems(currentPage++, itemsPerPage,url);
if (result == null || result.Count() == 0)
{
hasMoreItems = false;
}
else
{
resultCount = (uint)result.Count();
await dispatcher.RunAsync(
CoreDispatcherPriority.Normal,
() =>
{
foreach (I item in result)
this.Add(item);
});
}
return new LoadMoreItemsResult() { Count = resultCount };
}).AsAsyncOperation<LoadMoreItemsResult>();
}
}
public class StructList
{
public string Name { get; set; }
}
public class ItemsDataSource : IIncrementalSource<StructList>
{
private List<StructList> persons;
public ItemsDataSource()
{
persons = new List<StructList>();
//for (int i = 0; i < 1024; i++)
// {
// var p = new StructList { Name = "Person " + i };
// persons.Add(p);
// }
}
public async Task<IEnumerable<StructList>> GetPagedItems(int pageIndex, int pageSize,string url)
{
if (persons.Count > 10000) //you wriiten if (lastItem == 10000),assuming max items 10000
return null;
//If you want only 10 items and url returns more than 10 at a time
var result = (from p in persons
select p).Skip(pageIndex * pageSize).Take(pageSize);
if (result == null)
{
List<KeyValuePair<string, string>> postData = new List<KeyValuePair<string, string>>();
postData.Add(new KeyValuePair<string, string>("part", pageIndex.ToString()));
string JSonData = await WebService.get_post_respone(url, postData);
var items = JsonConvert.DeserializeObject<List<StructList>>(JSonData);
foreach (var item in items)
persons.Add(item);
return await Task.Run<IEnumerable<StructList>>(() =>
{
result = (from p in persons
select p).Skip(pageIndex * pageSize).Take(pageSize);
return result;
});
}
else
return result;
}
}
For more information Refer this Link
i find a way to load data with ISupportIncrementalLoading interface and my problem is how can tell to listview to get every 10 item per page.
how can say to download next part
this is my code in class .
structList is class model for objects.
public sealed partial class MainPage : Page
{
public string category;
public MainPage()
{
this.InitializeComponent();
}
protected async override void OnNavigatedTo(NavigationEventArgs e)
{
myListView.ItemsSource = new ItemsDataSource();
}
}
class ItemsDataSource : ObservableCollection<StructList>, ISupportIncrementalLoading
{
public int lastItem = 0;
public string part =0;
public bool HasMoreItems
{
get
{
if (lastItem == 10000)
{
return false;
}
else
{
return true;
}
}
}
public IAsyncOperation<LoadMoreItemsResult> LoadMoreItemsAsync(uint count)
{
CoreDispatcher coreDispatcher = Window.Current.Dispatcher;
return Task.Run<LoadMoreItemsResult>(async () =>
{
await coreDispatcher.RunAsync(CoreDispatcherPriority.Normal,
() =>
{
});
//get data by part
//part in my server start with 0 and later 1,2,3...
List<StructList> items = new List<StructList>();
List<KeyValuePair<string, string>> postData = new List<KeyValuePair<string, string>>();
postData.Add(new KeyValuePair<string, string>("part", part));
string JSonData = await WebService.get_post_respone(url, postData);
items = JsonConvert.DeserializeObject<List<StructList>>(JSonData);
await coreDispatcher.RunAsync(CoreDispatcherPriority.Normal,
() =>
{
foreach (StructList item in items)
{
this.Add(item);
}
});
return new LoadMoreItemsResult() { Count =count };
}).AsAsyncOperation<LoadMoreItemsResult>();
}
}You can use
<ScrollViewer x:Name="scrollViewer"
Loaded="scrollViewer_Loaded"
ViewChanged="scrollViewer_ViewChanged">
<StackPanel Orientation="Vertical">
<ProgressRing IsActive="{x:Bind IsPullRefresh,Mode=OneWay}" Height="30"></ProgressRing>
<ListView x:Name="list" ItemsSource="{x:Bind Items}" ></ListView>
</StackPanel>
</ScrollViewer>
</Grid>
public sealed partial class MainPage : Page, INotifyPropertyChanged
{
public ObservableCollection<object> Items { get; set; }
public bool IsPullRefresh
{
get
{
return _isPullRefresh;
}
set
{
_isPullRefresh = value;
OnPropertyChanged(nameof(IsPullRefresh));
}
}
bool _isPullRefresh = false;
public MainPage()
{
this.InitializeComponent();
Items = new ObservableCollection<object>();
for (int i = 0; i < 40; i++)
{
Items.Add(i);
}
}
public event PropertyChangedEventHandler PropertyChanged;
public void OnPropertyChanged(string name)
{
this.PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(name));
}
private void scrollViewer_Loaded(object sender, RoutedEventArgs e)
{
scrollViewer.ChangeView(null, 30, null);
}
private async void scrollViewer_ViewChanged(object sender, ScrollViewerViewChangedEventArgs e)
{
var sv = sender as ScrollViewer;
if (!e.IsIntermediate)
{
if (sv.VerticalOffset == 0.0)
{
IsPullRefresh = true;
await Task.Delay(2000);
for (int i = 0; i < 5; i++)
{
Items.Insert(0, i);
}
sv.ChangeView(null, 30, null);
}
IsPullRefresh = false;
}
}
}
If you can see Chinese,http://www.cnblogs.com/manupstairs/p/5184386.html
