原文:

在手机App中，如果有一个展示信息的列表，通常会展示很少一部分，当用户滑动到列表底部时，再加载更多内容。这样有两个好处，提高程序性能，减少网络流量。这篇博客中，将介绍如何在WPF ListView中实现这个功能。

实现思路：为ListView新增一个附加属性，用来绑定当下拉到底部时触发增加列表内容的功能。

XAML:

ScrollViewerMonitor:

public class ScrollViewerMonitor    {        public static ICommand GetAtEndCommand(DependencyObject obj)        {            return (ICommand)obj.GetValue(AtEndCommandProperty);        }        public static void SetAtEndCommand(DependencyObject obj, ICommand value)        {            obj.SetValue(AtEndCommandProperty, value);        }        public static readonly DependencyProperty AtEndCommandProperty =            DependencyProperty.RegisterAttached("AtEndCommand", typeof(ICommand),                 typeof(ScrollViewerMonitor), new PropertyMetadata(OnAtEndCommandChanged));        public static void OnAtEndCommandChanged(            DependencyObject d, DependencyPropertyChangedEventArgs e)        {            FrameworkElement element = (FrameworkElement)d;            if (element != null)            {                element.Loaded -= element_Loaded;                element.Loaded += element_Loaded;            }        }        private static void element_Loaded(object sender, RoutedEventArgs e)        {            FrameworkElement element = (FrameworkElement)sender;            element.Loaded -= element_Loaded;            ScrollViewer scrollViewer = FindChildOfType
        
         (element);            if(scrollViewer == null)            {                throw new InvalidOperationException("ScrollViewer not found.");            }            scrollViewer.ScrollChanged += delegate             {                bool atBottom = scrollViewer.VerticalOffset                                  >= scrollViewer.ScrollableHeight;                if(atBottom)                {                    var atEnd = GetAtEndCommand(element);                    if(atEnd != null)                    {                        atEnd.Execute(null);                    }                }            };        }        private static T FindChildOfType
         
          (DependencyObject root) where T : class        {            var queue = new Queue
          
           ();            queue.Enqueue(root);            while (queue.Count > 0)            {                DependencyObject current = queue.Dequeue();                for (int i = VisualTreeHelper.GetChildrenCount(current) - 1; 0 <= i; i--)                {                    var child = VisualTreeHelper.GetChild(current, i);                    var typedChild = child as T;                    if (typedChild != null)                    {                        return typedChild;                    }                    queue.Enqueue(child);                }            }            return null;        }    }
          
         
        

MainViewModel:

public class MainViewModel : INotifyPropertyChanged    {        public MainViewModel()        {            _busy = false;            AddMoreItems();            fetchMoreDataCommand = new DelegateCommand(() => {                ThreadPool.QueueUserWorkItem(                    delegate                    {                        Busy = true;                        Thread.Sleep(3000);                        App.Current.Dispatcher.BeginInvoke(new Action(()=> {                            AddMoreItems();                            Busy = false;                        }));                    });            });        }        private void AddMoreItems()        {            int start = items.Count;            int end = start + 10;            for (int i = start; i < end; i++)            {                items.Add("Item " + i);            }        }        readonly DelegateCommand fetchMoreDataCommand;        public ICommand FetchMoreDataCommand        {            get            {                return fetchMoreDataCommand;            }        }        private ObservableCollection
        
          items = new ObservableCollection
         
          ();        public ObservableCollection
          
            Items        {            get            {                return items;            }        }        private bool _busy;        public bool Busy        {            get            {                return _busy;            }            set            {                if(_busy != value)                {                    _busy = value;                    OnPropertyChanged("Busy");                }            }        }        public event PropertyChangedEventHandler PropertyChanged;        protected virtual void OnPropertyChanged(string propertyName)        {            if(PropertyChanged != null)            {                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));            }        }    }
          
         
        

Busy属性用来决定是否显示Loading。

运行效果：

感谢您的阅读！代码点击下载。