我有一个设置为水平滚动的 WPF 列表框。 ItemsSource 绑定到我的 ViewModel 类中的 ObservableCollection。每次添加新项目时，我都希望 ListBox 向右滚动以便可以查看新项目。
ListBox 是在 DataTemplate 中定义的，因此我无法在我的代码隐藏文件中按名称访问 ListBox。
如何让 ListBox 始终滚动以显示最新添加的项目？
我想知道 ListBox 何时添加了新项目，但我没有看到执行此操作的事件。
【问题讨论】：
您可以通过使用附加属性来扩展 ListBox 的行为。在您的情况下，我将定义一个名为 ScrollOnNewItem 的附加属性，当设置为 true 时，它会钩入列表框项目源的 INotifyCollectionChanged 事件，并在检测到新项目时将列表框滚动到它。
例子：
class ListBoxBehavior
{
static readonly Dictionary<ListBox, Capture> Associations =
new Dictionary<ListBox, Capture>();
public static bool GetScrollOnNewItem(DependencyObject obj)
{
return (bool)obj.GetValue(ScrollOnNewItemProperty);
}
public static void SetScrollOnNewItem(DependencyObject obj, bool value)
{
obj.SetValue(ScrollOnNewItemProperty, value);
}
public static readonly DependencyProperty ScrollOnNewItemProperty =
DependencyProperty.RegisterAttached(
"ScrollOnNewItem",
typeof(bool),
typeof(ListBoxBehavior),
new UIPropertyMetadata(false, OnScrollOnNewItemChanged));
public static void OnScrollOnNewItemChanged(
DependencyObject d,
DependencyPropertyChangedEventArgs e)
{
var listBox = d as ListBox;
if (listBox == null) return;
bool oldValue = (bool)e.OldValue, newValue = (bool)e.NewValue;
if (newValue == oldValue) return;
if (newValue)
{
listBox.Loaded += ListBox_Loaded;
listBox.Unloaded += ListBox_Unloaded;
var itemsSourcePropertyDescriptor = TypeDescriptor.GetProperties(listBox)["ItemsSource"];
itemsSourcePropertyDescriptor.AddValueChanged(listBox, ListBox_ItemsSourceChanged);
}
else
{
listBox.Loaded -= ListBox_Loaded;
listBox.Unloaded -= ListBox_Unloaded;
if (Associations.ContainsKey(listBox))
Associations[listBox].Dispose();
var itemsSourcePropertyDescriptor = TypeDescriptor.GetProperties(listBox)["ItemsSource"];
itemsSourcePropertyDescriptor.RemoveValueChanged(listBox, ListBox_ItemsSourceChanged);
}
}
private static void ListBox_ItemsSourceChanged(object sender, EventArgs e)
{
var listBox = (ListBox)sender;
if (Associations.ContainsKey(listBox))
Associations[listBox].Dispose();
Associations[listBox] = new Capture(listBox);
}
static void ListBox_Unloaded(object sender, RoutedEventArgs e)
{
var listBox = (ListBox)sender;
if (Associations.ContainsKey(listBox))
Associations[listBox].Dispose();
listBox.Unloaded -= ListBox_Unloaded;
}
static void ListBox_Loaded(object sender, RoutedEventArgs e)
{
var listBox = (ListBox)sender;
var incc = listBox.Items as INotifyCollectionChanged;
if (incc == null) return;
listBox.Loaded -= ListBox_Loaded;
Associations[listBox] = new Capture(listBox);
}
class Capture : IDisposable
{
private readonly ListBox listBox;
private readonly INotifyCollectionChanged incc;
public Capture(ListBox listBox)
{
this.listBox = listBox;
incc = listBox.ItemsSource as INotifyCollectionChanged;
if (incc != null)
{
incc.CollectionChanged += incc_CollectionChanged;
}
}
void incc_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
{
if (e.Action == NotifyCollectionChangedAction.Add)
{
listBox.ScrollIntoView(e.NewItems[0]);
listBox.SelectedItem = e.NewItems[0];
}
}
public void Dispose()
{
if (incc != null)
incc.CollectionChanged -= incc_CollectionChanged;
}
}
}
用法：
<ListBox ItemsSource="{Binding SourceCollection}"
lb:ListBoxBehavior.ScrollOnNewItem="true"/>
更新根据 Andrej 在下面的 cmets 中的建议，我添加了钩子来检测 ListBox 的 ItemsSource 的变化。
【讨论】：
ScrollIntoView 方法和SelectedItem 属性只是获取第一个对象，所以它总是在顶部，当我添加不同的字符串时它会向下滚动。我通过添加时间戳来防止这种行为。毫秒到字符串:)
<ItemsControl ItemsSource="{Binding SourceCollection}">
<i:Interaction.Behaviors>
<Behaviors:ScrollOnNewItem/>
</i:Interaction.Behaviors>
</ItemsControl>
public class ScrollOnNewItem : Behavior<ItemsControl>
{
protected override void OnAttached()
{
AssociatedObject.Loaded += OnLoaded;
AssociatedObject.Unloaded += OnUnLoaded;
}
protected override void OnDetaching()
{
AssociatedObject.Loaded -= OnLoaded;
AssociatedObject.Unloaded -= OnUnLoaded;
}
private void OnLoaded(object sender, RoutedEventArgs e)
{
var incc = AssociatedObject.ItemsSource as INotifyCollectionChanged;
if (incc == null) return;
incc.CollectionChanged += OnCollectionChanged;
}
private void OnUnLoaded(object sender, RoutedEventArgs e)
{
var incc = AssociatedObject.ItemsSource as INotifyCollectionChanged;
if (incc == null) return;
incc.CollectionChanged -= OnCollectionChanged;
}
private void OnCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
{
if(e.Action == NotifyCollectionChangedAction.Add)
{
int count = AssociatedObject.Items.Count;
if (count == 0)
return;
var item = AssociatedObject.Items[count - 1];
var frameworkElement = AssociatedObject.ItemContainerGenerator.ContainerFromItem(item) as FrameworkElement;
if (frameworkElement == null) return;
frameworkElement.BringIntoView();
}
}
【讨论】：
Behavior(Of T) 类！看起来更简洁易读。
BringIntoView() 似乎不起作用。在调试中，我可以看到代码正在执行，但 ListBox 没有滚动。我看到其他人有类似的问题：stackoverflow.com/questions/12430923/…
我找到了一种非常巧妙的方法，只需更新列表框 scrollViewer 并将位置设置到底部。例如，在诸如 SelectionChanged 的 ListBox 事件之一中调用此函数。
private void UpdateScrollBar(ListBox listBox)
{
if (listBox != null)
{
var border = (Border)VisualTreeHelper.GetChild(listBox, 0);
var scrollViewer = (ScrollViewer)VisualTreeHelper.GetChild(border, 0);
scrollViewer.ScrollToBottom();
}
}
【讨论】：
ListBox.ScrollIntoView 不起作用
我使用这个解决方案：http://michlg.wordpress.com/2010/01/16/listbox-automatically-scroll-currentitem-into-view/。
即使您将列表框的 ItemsSource 绑定到在非 UI 线程中操作的 ObservableCollection，它也可以工作。
【讨论】：
添加新项目时，此附加行为会自动将列表框滚动到底部。
<ListBox ItemsSource="{Binding LoggingStream}">
<i:Interaction.Behaviors>
<behaviors:ScrollOnNewItemBehavior
IsActiveScrollOnNewItem="{Binding IfFollowTail, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"/>
</i:Interaction.Behaviors>
</ListBox>
在您的ViewModel 中，您可以绑定到布尔值IfFollowTail { get; set; } 来控制是否启用自动滚动。
行为做所有正确的事情：
IfFollowTail=false，则 ListBox 不再滚动到新项目的底部。IfFollowTail=true 后，ListBox 会立即滚动到底部，并继续滚动。public class ScrollOnNewItemBehavior : Behavior<ListBox>
{
public static readonly DependencyProperty IsActiveScrollOnNewItemProperty = DependencyProperty.Register(
name: "IsActiveScrollOnNewItem",
propertyType: typeof(bool),
ownerType: typeof(ScrollOnNewItemBehavior),
typeMetadata: new PropertyMetadata(defaultValue: true, propertyChangedCallback:PropertyChangedCallback));
private static void PropertyChangedCallback(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs dependencyPropertyChangedEventArgs)
{
// Intent: immediately scroll to the bottom if our dependency property changes.
ScrollOnNewItemBehavior behavior = dependencyObject as ScrollOnNewItemBehavior;
if (behavior == null)
{
return;
}
behavior.IsActiveScrollOnNewItemMirror = (bool)dependencyPropertyChangedEventArgs.NewValue;
if (behavior.IsActiveScrollOnNewItemMirror == false)
{
return;
}
ListboxScrollToBottom(behavior.ListBox);
}
public bool IsActiveScrollOnNewItem
{
get { return (bool)this.GetValue(IsActiveScrollOnNewItemProperty); }
set { this.SetValue(IsActiveScrollOnNewItemProperty, value); }
}
public bool IsActiveScrollOnNewItemMirror { get; set; } = true;
protected override void OnAttached()
{
this.AssociatedObject.Loaded += this.OnLoaded;
this.AssociatedObject.Unloaded += this.OnUnLoaded;
}
protected override void OnDetaching()
{
this.AssociatedObject.Loaded -= this.OnLoaded;
this.AssociatedObject.Unloaded -= this.OnUnLoaded;
}
private IDisposable rxScrollIntoView;
private void OnLoaded(object sender, RoutedEventArgs e)
{
var changed = this.AssociatedObject.ItemsSource as INotifyCollectionChanged;
if (changed == null)
{
return;
}
// Intent: If we scroll into view on every single item added, it slows down to a crawl.
this.rxScrollIntoView = changed
.ToObservable()
.ObserveOn(new EventLoopScheduler(ts => new Thread(ts) { IsBackground = true}))
.Where(o => this.IsActiveScrollOnNewItemMirror == true)
.Where(o => o.NewItems?.Count > 0)
.Sample(TimeSpan.FromMilliseconds(180))
.Subscribe(o =>
{
this.Dispatcher.BeginInvoke((Action)(() =>
{
ListboxScrollToBottom(this.ListBox);
}));
});
}
ListBox ListBox => this.AssociatedObject;
private void OnUnLoaded(object sender, RoutedEventArgs e)
{
this.rxScrollIntoView?.Dispose();
}
/// <summary>
/// Scrolls to the bottom. Unlike other methods, this works even if there are duplicate items in the listbox.
/// </summary>
private static void ListboxScrollToBottom(ListBox listBox)
{
if (VisualTreeHelper.GetChildrenCount(listBox) > 0)
{
Border border = (Border)VisualTreeHelper.GetChild(listBox, 0);
ScrollViewer scrollViewer = (ScrollViewer)VisualTreeHelper.GetChild(border, 0);
scrollViewer.ScrollToBottom();
}
}
}
最后，添加这个扩展方法，这样我们就可以使用所有的 RX 优点：
public static class ListBoxEventToObservableExtensions
{
/// <summary>Converts CollectionChanged to an observable sequence.</summary>
public static IObservable<NotifyCollectionChangedEventArgs> ToObservable<T>(this T source)
where T : INotifyCollectionChanged
{
return Observable.FromEvent<NotifyCollectionChangedEventHandler, NotifyCollectionChangedEventArgs>(
h => (sender, e) => h(e),
h => source.CollectionChanged += h,
h => source.CollectionChanged -= h);
}
}
您需要将Reactive Extensions 添加到您的项目中。我推荐NuGet。
【讨论】：
Datagrid的解决方案（ListBox同理，只是用ListBox类代替DataGrid）
private void OnCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
{
if (e.Action == NotifyCollectionChangedAction.Add)
{
int count = AssociatedObject.Items.Count;
if (count == 0)
return;
var item = AssociatedObject.Items[count - 1];
if (AssociatedObject is DataGrid)
{
DataGrid grid = (AssociatedObject as DataGrid);
grid.Dispatcher.BeginInvoke((Action)(() =>
{
grid.UpdateLayout();
grid.ScrollIntoView(item, null);
}));
}
}
}
【讨论】：
我对提出的解决方案不满意。
这就是我最终的结果。也许它会节省一些时间。
public class AutoScroll : Behavior<ItemsControl>
{
public static readonly DependencyProperty ModeProperty = DependencyProperty.Register(
"Mode", typeof(AutoScrollMode), typeof(AutoScroll), new PropertyMetadata(AutoScrollMode.VerticalWhenInactive));
public AutoScrollMode Mode
{
get => (AutoScrollMode) GetValue(ModeProperty);
set => SetValue(ModeProperty, value);
}
protected override void OnAttached()
{
base.OnAttached();
AssociatedObject.Loaded += OnLoaded;
AssociatedObject.Unloaded += OnUnloaded;
}
protected override void OnDetaching()
{
Clear();
AssociatedObject.Loaded -= OnLoaded;
AssociatedObject.Unloaded -= OnUnloaded;
base.OnDetaching();
}
private static readonly DependencyProperty ItemsCountProperty = DependencyProperty.Register(
"ItemsCount", typeof(int), typeof(AutoScroll), new PropertyMetadata(0, (s, e) => ((AutoScroll)s).OnCountChanged()));
private ScrollViewer _scroll;
private void OnLoaded(object sender, RoutedEventArgs e)
{
var binding = new Binding("ItemsSource.Count")
{
Source = AssociatedObject,
Mode = BindingMode.OneWay
};
BindingOperations.SetBinding(this, ItemsCountProperty, binding);
_scroll = AssociatedObject.FindVisualChild<ScrollViewer>() ?? throw new NotSupportedException("ScrollViewer was not found!");
}
private void OnUnloaded(object sender, RoutedEventArgs e)
{
Clear();
}
private void Clear()
{
BindingOperations.ClearBinding(this, ItemsCountProperty);
}
private void OnCountChanged()
{
var mode = Mode;
if (mode == AutoScrollMode.Vertical)
{
_scroll.ScrollToBottom();
}
else if (mode == AutoScrollMode.Horizontal)
{
_scroll.ScrollToRightEnd();
}
else if (mode == AutoScrollMode.VerticalWhenInactive)
{
if (_scroll.IsKeyboardFocusWithin) return;
_scroll.ScrollToBottom();
}
else if (mode == AutoScrollMode.HorizontalWhenInactive)
{
if (_scroll.IsKeyboardFocusWithin) return;
_scroll.ScrollToRightEnd();
}
}
}
public enum AutoScrollMode
{
/// <summary>
/// No auto scroll
/// </summary>
Disabled,
/// <summary>
/// Automatically scrolls horizontally, but only if items control has no keyboard focus
/// </summary>
HorizontalWhenInactive,
/// <summary>
/// Automatically scrolls vertically, but only if itmes control has no keyboard focus
/// </summary>
VerticalWhenInactive,
/// <summary>
/// Automatically scrolls horizontally regardless of where the focus is
/// </summary>
Horizontal,
/// <summary>
/// Automatically scrolls vertically regardless of where the focus is
/// </summary>
Vertical
}
【讨论】：
我发现执行此操作的最直接的方法，尤其是对于绑定到数据源的列表框（或列表视图），是将其与集合更改事件挂钩。 您可以在列表框的 DataContextChanged 事件中非常轻松地做到这一点：
//in xaml <ListView x:Name="LogView" DataContextChanged="LogView_DataContextChanged">
private void LogView_DataContextChanged(object sender, DependencyPropertyChangedEventArgs e)
{
var src = LogView.Items.SourceCollection as INotifyCollectionChanged;
src.CollectionChanged += (obj, args) => { LogView.Items.MoveCurrentToLast(); LogView.ScrollIntoView(LogView.Items.CurrentItem); };
}
这实际上只是我找到的所有其他答案的组合。 我觉得这是一个微不足道的功能，我们不应该花费这么多时间（和代码行）来做。
如果只有 Autoscroll = true 属性。叹。
【讨论】：
我找到了一种更简单的方法，可以帮助我解决类似的问题，只需几行代码，无需创建自定义行为。检查我对这个问题的回答（并点击里面的链接）：
wpf(C#) DataGrid ScrollIntoView - how to scroll to the first row that is not shown?
它适用于 ListBox、ListView 和 DataGrid。
【讨论】：
所以我在这个主题中读到的内容对于一个简单的动作来说有点复杂。
所以我订阅了 scrollchanged 事件，然后我使用了这段代码：
private void TelnetListBox_OnScrollChanged(object sender, ScrollChangedEventArgs e)
{
var scrollViewer = ((ScrollViewer)e.OriginalSource);
scrollViewer.ScrollToEnd();
}
奖金：
之后，我做了一个复选框，我可以在其中设置我想要使用自动滚动功能的时间，我说如果我看到一些有趣的信息，我有时会忘记取消选中列表框。所以我决定创建一个智能的自动滚动列表框，它会对我的鼠标操作做出反应。
private void TelnetListBox_OnScrollChanged(object sender, ScrollChangedEventArgs e)
{
var scrollViewer = ((ScrollViewer)e.OriginalSource);
scrollViewer.ScrollToEnd();
if (AutoScrollCheckBox.IsChecked != null && (bool)AutoScrollCheckBox.IsChecked)
scrollViewer.ScrollToEnd();
if (_isDownMouseMovement)
{
var verticalOffsetValue = scrollViewer.VerticalOffset;
var maxVerticalOffsetValue = scrollViewer.ExtentHeight - scrollViewer.ViewportHeight;
if (maxVerticalOffsetValue < 0 || verticalOffsetValue == maxVerticalOffsetValue)
{
// Scrolled to bottom
AutoScrollCheckBox.IsChecked = true;
_isDownMouseMovement = false;
}
else if (verticalOffsetValue == 0)
{
}
}
}
private bool _isDownMouseMovement = false;
private void TelnetListBox_OnPreviewMouseWheel(object sender, MouseWheelEventArgs e)
{
if (e.Delta > 0)
{
_isDownMouseMovement = false;
AutoScrollCheckBox.IsChecked = false;
}
if (e.Delta < 0)
{
_isDownMouseMovement = true;
}
}
当我按下按钮时，复选框被选中，如果我用鼠标滚轮向上滚动，则将我的视图保持在底部，复选框将被取消选中，您可以浏览您的列表框。
【讨论】：
这是我使用的有效解决方案，可能对其他人有所帮助；
statusWindow.SelectedIndex = statusWindow.Items.Count - 1;
statusWindow.UpdateLayout();
statusWindow.ScrollIntoView(statusWindow.SelectedItem);
statusWindow.UpdateLayout();
【讨论】：
这对我有用：
DirectoryInfo di = new DirectoryInfo(folderBrowserDialog1.SelectedPath);
foreach (var fi in di.GetFiles("*", SearchOption.AllDirectories))
{
int count = Convert.ToInt32(listBox1.Items.Count); // counts every listbox entry
listBox1.Items.Add(count + " - " + fi.Name); // display entrys
listBox1.TopIndex = count; // scroll to the last entry
}
【讨论】：