MVVM WPF 中的 ListBox 滚动事件 [英] ListBox scrolling event in MVVM WPF
本文介绍了MVVM WPF 中的 ListBox 滚动事件的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
有没有办法以 MVVM 的方式在 WPF (Windows Phone7) 中挂钩滚动事件?我想检测列表何时滚动到底部，然后执行某些操作.我试过这样的事情，但显然它不会工作:
<i:Interaction.Triggers><i:EventTrigger EventName="点击"><i:InvokeCommandAction Command="{Binding ListBoxClick}"/></i:EventTrigger><i:EventTrigger EventName="滚动"><i:InvokeCommandAction Command="{Binding ListBoxScroll}"/></i:EventTrigger></i:Interaction.Triggers>(……)</列表框> 解决方案
在这种情况下，我总是看附加行为的方向，因为我们需要一个独立的解决方案，可以在旁边工作UI 和 MVVM 风格.附加行为 - 是一个附加属性，它有一个事件处理程序来改变这个属性，所有的逻辑都在这个处理程序中实现.
在这种情况下，您需要传递一个指示行为开始的布尔值，以及当我们的条件执行时执行的命令 - 滚动到 ListBox 的末尾.
我创建了一个示例行为，其中关键逻辑在这里:
private static void scrollViewerScrollChanged(object sender, ScrollChangedEventArgs e){var scrollViewer = sender as ScrollViewer;如果(滚动查看器！= null){//这里我们判断是否到达底部如果(scrollViewer.VerticalOffset == scrollViewer.ScrollableHeight){命令 = GetCommand(listBox);//执行命令命令.执行(列表框)；}}}使用示例:
XAML
<local:TestViewModel/></Window.DataContext><窗口.资源><x:Array x:Key="TestArray" Type="{x:Type sys:String}"><sys:String>Test1</sys:String><sys:String>Test2</sys:String><sys:String>Test3</sys:String><sys:String>Test4</sys:String><sys:String>Test5</sys:String><sys:String>Test6</sys:String><sys:String>Test7</sys:String><sys:String>Test8</sys:String><sys:String>Test9</sys:String><sys:String>Test10</sys:String></x:数组></Window.Resources><网格><列表框名称=测试列表框"AttachedBehaviors:ScrollingToBottomBehavior.IsEnabled="True"AttachedBehaviors:ScrollingToBottomBehavior.Command="{Binding TestButtonCommand}"ItemsSource="{StaticResource TestArray}"高度=50"/></网格> TestViewModel
公共类TestViewModel{私人 ICommand _testButtonCommand = null;公共 ICommand 测试按钮命令{得到{if (_testButtonCommand == null){_testButtonCommand = new RelayCommand(param => this.TestButton(), null);}返回 _testButtonCommand;}}私有无效 TestButton(){MessageBox.Show("测试命令执行");}}ScrollingToBottomBehavior
公共类ScrollingToBottomBehavior{#region 私人部分私有静态列表框 listBox = null;私有静态 ICommand 命令 = null;#endregion#region IsEnabledPropertypublic static readonly DependencyProperty IsEnabledProperty;public static void SetIsEnabled(DependencyObject DepObject, 字符串值){DepObject.SetValue(IsEnabledProperty, value);}public static bool GetIsEnabled(DependencyObject DepObject){返回(布尔)DepObject.GetValue(IsEnabledProperty)；}#endregion#region 命令属性public static readonly DependencyProperty CommandProperty;public static void SetCommand(DependencyObject DepObject, ICommand 值){DepObject.SetValue(CommandProperty, value);}公共静态 ICommand GetCommand(DependencyObject DepObject){返回(ICommand)DepObject.GetValue(CommandProperty)；}静态 ScrollingToBottomBehavior(){IsEnabledProperty = DependencyProperty.RegisterAttached("IsEnabled",类型(布尔)，typeof(ScrollingToBottomBehavior),新的 UIPropertyMetadata(false, IsFrontTurn));CommandProperty = DependencyProperty.RegisterAttached("Command",类型(ICommand)，typeof(ScrollingToBottomBehavior));}#endregionprivate static void IsFrontTurn(DependencyObject sender, DependencyPropertyChangedEventArgs e){listBox = 发件人为列表框；如果(列表框 == 空){返回;}if (e.NewValue is bool && ((bool)e.NewValue) == true){listBox.Loaded += new RoutedEventHandler(listBoxLoaded);}别的{listBox.Loaded -= new RoutedEventHandler(listBoxLoaded);}}private static void listBoxLoaded(object sender, RoutedEventArgs e){var scrollViewer = GetFirstChildOfType(listBox);如果(滚动查看器！= null){scrollViewer.ScrollChanged += new ScrollChangedEventHandler(scrollViewerScrollChanged);}}#region GetFirstChildOfTypeprivate static T GetFirstChildOfType(DependencyObject dependencyObject) 其中 T : DependencyObject{if (dependencyObject == null){返回空；}for (var i = 0; i < VisualTreeHelper.GetChildrenCount(dependencyObject); i++){var child = VisualTreeHelper.GetChild(dependencyObject, i);var 结果 = (child as T) ??GetFirstChildOfType(child);如果(结果！= null){返回结果；}}返回空；}#endregionprivate static void scrollViewerScrollChanged(object sender, ScrollChangedEventArgs e){var scrollViewer = sender as ScrollViewer;如果(滚动查看器！= null){如果(scrollViewer.VerticalOffset == scrollViewer.ScrollableHeight){命令 = GetCommand(listBox);命令.执行(列表框)；}}}} <块引用>
完整的示例项目可用 <代码>此处.
Is there a way to hook to scroll event in WPF (Windows Phone7), in a MVVM manner? I'd like to detect when the list is scrolled to the bottom, and then do something. I tried something like this, but obviously it won't work:
<ListBox ItemsSource="{Binding Places}" SelectedItem="{Binding SelectedPlace, Mode=TwoWay}">
<i:Interaction.Triggers>
<i:EventTrigger EventName="Tap">
<i:InvokeCommandAction Command="{Binding ListBoxClick}"/>
</i:EventTrigger>
<i:EventTrigger EventName="Scroll">
<i:InvokeCommandAction Command="{Binding ListBoxScroll}"/>
</i:EventTrigger>
</i:Interaction.Triggers>
(...)
</ListBox>
解决方案
In this situation, I always look in the direction of attached behavior, because we need an independent solution that would work on the side UI and in the MVVM style. Attached behavior - is an attached property, which has an event handler to change this property and all the logic is implemented in this handler.
In this case you need to pass a Boolean value that indicates the beginning of behavior, and the command, what be executed when our condition is perform - scroll to the end of ListBox.
I created an example behavior where the key logic is here:
private static void scrollViewerScrollChanged(object sender, ScrollChangedEventArgs e)
{
var scrollViewer = sender as ScrollViewer;
if (scrollViewer != null)
{
// Here we determine if the bottom reached
if (scrollViewer.VerticalOffset == scrollViewer.ScrollableHeight)
{
command = GetCommand(listBox);
// Execute the command
command.Execute(listBox);
}
}
}
Example of using:
XAML
<Window.DataContext>
<local:TestViewModel />
</Window.DataContext>
<Window.Resources>
<x:Array x:Key="TestArray" Type="{x:Type sys:String}">
<sys:String>Test1</sys:String>
<sys:String>Test2</sys:String>
<sys:String>Test3</sys:String>
<sys:String>Test4</sys:String>
<sys:String>Test5</sys:String>
<sys:String>Test6</sys:String>
<sys:String>Test7</sys:String>
<sys:String>Test8</sys:String>
<sys:String>Test9</sys:String>
<sys:String>Test10</sys:String>
</x:Array>
</Window.Resources>
<Grid>
<ListBox Name="TestListBox"
AttachedBehaviors:ScrollingToBottomBehavior.IsEnabled="True"
AttachedBehaviors:ScrollingToBottomBehavior.Command="{Binding TestButtonCommand}"
ItemsSource="{StaticResource TestArray}"
Height="50" />
</Grid>
TestViewModel
public class TestViewModel
{
private ICommand _testButtonCommand = null;
public ICommand TestButtonCommand
{
get
{
if (_testButtonCommand == null)
{
_testButtonCommand = new RelayCommand(param => this.TestButton(), null);
}
return _testButtonCommand;
}
}
private void TestButton()
{
MessageBox.Show("Test command execute");
}
}
ScrollingToBottomBehavior
public class ScrollingToBottomBehavior
{
#region Private Section
private static ListBox listBox = null;
private static ICommand command = null;
#endregion
#region IsEnabledProperty
public static readonly DependencyProperty IsEnabledProperty;
public static void SetIsEnabled(DependencyObject DepObject, string value)
{
DepObject.SetValue(IsEnabledProperty, value);
}
public static bool GetIsEnabled(DependencyObject DepObject)
{
return (bool)DepObject.GetValue(IsEnabledProperty);
}
#endregion
#region CommandProperty
public static readonly DependencyProperty CommandProperty;
public static void SetCommand(DependencyObject DepObject, ICommand value)
{
DepObject.SetValue(CommandProperty, value);
}
public static ICommand GetCommand(DependencyObject DepObject)
{
return (ICommand)DepObject.GetValue(CommandProperty);
}
static ScrollingToBottomBehavior()
{
IsEnabledProperty = DependencyProperty.RegisterAttached("IsEnabled",
typeof(bool),
typeof(ScrollingToBottomBehavior),
new UIPropertyMetadata(false, IsFrontTurn));
CommandProperty = DependencyProperty.RegisterAttached("Command",
typeof(ICommand),
typeof(ScrollingToBottomBehavior));
}
#endregion
private static void IsFrontTurn(DependencyObject sender, DependencyPropertyChangedEventArgs e)
{
listBox = sender as ListBox;
if (listBox == null)
{
return;
}
if (e.NewValue is bool && ((bool)e.NewValue) == true)
{
listBox.Loaded += new RoutedEventHandler(listBoxLoaded);
}
else
{
listBox.Loaded -= new RoutedEventHandler(listBoxLoaded);
}
}
private static void listBoxLoaded(object sender, RoutedEventArgs e)
{
var scrollViewer = GetFirstChildOfType<ScrollViewer>(listBox);
if (scrollViewer != null)
{
scrollViewer.ScrollChanged += new ScrollChangedEventHandler(scrollViewerScrollChanged);
}
}
#region GetFirstChildOfType
private static T GetFirstChildOfType<T>(DependencyObject dependencyObject) where T : DependencyObject
{
if (dependencyObject == null)
{
return null;
}
for (var i = 0; i < VisualTreeHelper.GetChildrenCount(dependencyObject); i++)
{
var child = VisualTreeHelper.GetChild(dependencyObject, i);
var result = (child as T) ?? GetFirstChildOfType<T>(child);
if (result != null)
{
return result;
}
}
return null;
}
#endregion
private static void scrollViewerScrollChanged(object sender, ScrollChangedEventArgs e)
{
var scrollViewer = sender as ScrollViewer;
if (scrollViewer != null)
{
if (scrollViewer.VerticalOffset == scrollViewer.ScrollableHeight)
{
command = GetCommand(listBox);
command.Execute(listBox);
}
}
}
}
Complete sample project is available
here.
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