我在网上看过样本，有些很难学。
我想学习如何理解ListView向下滚动的时间以及是否还有更多数据，如何在屏幕上显示ProgressRing时从互联网上获取数据。
对于我的示例，我使用JSON从PHP服务器获取数据，并且每个请求都从数据库中获取10个项目。
如果您能提供易于理解的样品，我们将非常感激。
答案 0 :(得分：1)
我找到了一种使用ISupportIncrementalLoading接口加载数据的方法，我的问题是如何告诉listview每页每10项。
怎么说下载下一部分
这是我课堂上的代码。
structList是对象的类模型。
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>();
}
}
答案 1 :(得分：1)
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;
}
}
了解更多信息Refer this Link
答案 2 :(得分：0)
您可以使用
<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;
}
}
}