C# FindVisualChild-获取ItemsControl中命名UI元素的属性
我使用C# FindVisualChild-获取ItemsControl中命名UI元素的属性,c#,wpf,xaml,itemscontrol,C#,Wpf,Xaml,Itemscontrol,我使用ItemsControl在运行时生成UI元素。UI生成成功，但如果无法获取生成的UI项的任何属性，例如标签的“内容”，或组合框的选择编辑项。我试图通过使用和获取这些属性，但总是得到NullReferenceException XAML中的ItemsControl如下所示： <ItemsControl Name="ListOfVideos"> <ItemsControl.Background>
ItemsControl选择编辑项。我试图通过使用和获取这些属性，但总是得到NullReferenceException
XAML中的ItemsControl
如下所示：
<ItemsControl Name="ListOfVideos">
<ItemsControl.Background>
<SolidColorBrush Color="Black" Opacity="0"/>
</ItemsControl.Background>
<ItemsControl.ItemTemplate>
<DataTemplate>
<Grid Margin="0,0,0,10">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="180"/>
<ColumnDefinition Width="400"/>
<ColumnDefinition Width="200"/>
</Grid.ColumnDefinitions>
<Image HorizontalAlignment="Left" Height="100" Width="175" x:Name="VideoThumbnailImage" Stretch="Fill" Source="{Binding VideoThumbnailURL}" Grid.Column="0"></Image>
<Label x:Name="VideoTitleLabel" Content="{Binding VideoTitleText}" Foreground="White" Grid.Column="1" VerticalAlignment="Top" FontSize="16" FontWeight="Bold"></Label>
<Label x:Name="VideoFileSizeLabel" Content="{Binding VideoTotalSizeText}" Foreground="White" FontSize="14" Grid.Column="1" Margin="0,0,0,35" VerticalAlignment="Bottom"></Label>
<Label x:Name="VideoProgressLabel" Content="{Binding VideoStatusText}" Foreground="White" FontSize="14" Grid.Column="1" VerticalAlignment="Bottom"></Label>
<ComboBox x:Name="VideoComboBox" SelectionChanged="VideoComboBox_SelectionChanged" Grid.Column="2" Width="147.731" Height="20" VerticalAlignment="Bottom" HorizontalAlignment="Center" Margin="0,0,0,50" ItemsSource="{Binding VideoQualitiesList}"></ComboBox>
<Label Content="Video Quality" Foreground="White" FontSize="14" VerticalAlignment="Top" Grid.Column="2" HorizontalAlignment="Center"></Label>
<Label Content="Audio Quality" Foreground="White" FontSize="14" VerticalAlignment="Bottom" HorizontalAlignment="Center" Margin="0,0,0,27" Grid.Column="2"></Label>
<Slider x:Name="VideoAudioSlider" Grid.Column="2" HorizontalAlignment="Center" VerticalAlignment="Bottom" Width="147.731" Maximum="{Binding AudioCount}"></Slider>
</Grid>
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
这就是我生成UI元素的方式
public class VideoMetadataDisplay
{
public string VideoTitleText { get; set; }
public int AudioCount { get; set; }
public string VideoThumbnailURL { get; set; }
public string VideoStatusText { get; set; }
public string VideoTotalSizeText { get; set; }
public List<string> VideoQualitiesList { get; set; }
}
public partial class PlaylistPage : Page
{
private void GetPlaylistMetadata()
{
List<VideoMetadataDisplay> newList = new List<VideoMetadataDisplay>();
//populate the list
ListOfVideos.ItemsSource = newList;
}
}
public class Utils
{
public childItem FindVisualChild<childItem>(DependencyObject obj)
where childItem : DependencyObject
{
for (int i = 0; i < VisualTreeHelper.GetChildrenCount(obj); i++)
{
DependencyObject child = VisualTreeHelper.GetChild(obj, i);
if (child != null && child is childItem)
{
return (childItem)child;
}
else
{
childItem childOfChild = FindVisualChild<childItem>(child);
if (childOfChild != null)
return childOfChild;
}
}
return null;
}
}
private void VideoComboBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
UIElement CurrentItem = (UIElement)ListOfVideos.ItemContainerGenerator.ContainerFromItem(ListOfVideos.Items.CurrentItem);
Utils utils = new Utils();
ContentPresenter CurrentContentPresenter = utils.FindVisualChild<ContentPresenter>(CurrentItem);
DataTemplate CurrentDataTemplate = CurrentContentPresenter.ContentTemplate;
Label VideoTitle = (Label)CurrentDataTemplate.FindName("VideoTitleLabel", CurrentContentPresenter);
string VideoTitleText = VideoTitle.Content.ToString();
MessageBox.Show(VideoTitleText);
}
公共类VideoMetadataDisplay
{
公共字符串VideoTitleText{get；set；}
公共整数音频计数{get；set；}
公共字符串VideoThumbnailURL{get；set；}
公共字符串VideoStatusText{get；set；}
公共字符串VideoTotalSizeText{get；set；}
公共列表VideoQualitiesList{get；set；}
}
公共部分类播放列表第页：第页
{
私有void getplaylaymetadata（）
{
List newList=新列表（）；
//填充列表
ListOfVideos.ItemsSource=newList；
}
}
这就是我试图获取UI元素属性的方法
public class VideoMetadataDisplay
{
public string VideoTitleText { get; set; }
public int AudioCount { get; set; }
public string VideoThumbnailURL { get; set; }
public string VideoStatusText { get; set; }
public string VideoTotalSizeText { get; set; }
public List<string> VideoQualitiesList { get; set; }
}
public partial class PlaylistPage : Page
{
private void GetPlaylistMetadata()
{
List<VideoMetadataDisplay> newList = new List<VideoMetadataDisplay>();
//populate the list
ListOfVideos.ItemsSource = newList;
}
}
public class Utils
{
public childItem FindVisualChild<childItem>(DependencyObject obj)
where childItem : DependencyObject
{
for (int i = 0; i < VisualTreeHelper.GetChildrenCount(obj); i++)
{
DependencyObject child = VisualTreeHelper.GetChild(obj, i);
if (child != null && child is childItem)
{
return (childItem)child;
}
else
{
childItem childOfChild = FindVisualChild<childItem>(child);
if (childOfChild != null)
return childOfChild;
}
}
return null;
}
}
private void VideoComboBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
UIElement CurrentItem = (UIElement)ListOfVideos.ItemContainerGenerator.ContainerFromItem(ListOfVideos.Items.CurrentItem);
Utils utils = new Utils();
ContentPresenter CurrentContentPresenter = utils.FindVisualChild<ContentPresenter>(CurrentItem);
DataTemplate CurrentDataTemplate = CurrentContentPresenter.ContentTemplate;
Label VideoTitle = (Label)CurrentDataTemplate.FindName("VideoTitleLabel", CurrentContentPresenter);
string VideoTitleText = VideoTitle.Content.ToString();
MessageBox.Show(VideoTitleText);
}
公共类Utils
{
公共子项FindVisualChild（DependencyObject obj）
where-childItem:DependencyObject
{
for（int i=0；i
每次尝试运行此操作时，FindVisualChild
总是返回其中一个标签（VideoTitleLabel
），而不是返回当前活动项的ContentPresenter
CurrentDataTemplate
随后为空，我无法从中获取任何UI元素。不可能FindVisualChild
返回一个标签
实例FindVisualChild
将结果强制转换为ContentPresenter
。由于Label
不是ContentPresenter
，这将引发InvalidCastException
。但在此之前，child is childItem
将返回false
，前提是child
类型为Label
，通用参数类型childItem
类型为ContentPresenter
，因此返回一个潜在的null
短版
访问数据模板
或查找控件以获取其绑定数据总是太复杂。直接访问数据源总是比较容易。
ItemsControl.SelectedItem
将返回所选项目的数据模型。你通常对容器不感兴趣
private void VideoComboBox_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
var listView = sender as ListView;
var item = listView.SelectedItem as VideoMetadataDisplay;
MessageBox.Show(item.VideoTitleText);
}
您的版本（FindVisualChild
改进）
FindVisualChild
的实现较弱。如果遍历遇到没有子节点的子节点，即参数obj
为null
，它将失败并引发异常。在调用VisualTreeHelper.GetChildrenCount（obj）
之前，必须检查参数obj
的null
，以避免引用null
此外，您不需要通过访问模板来搜索元素。您可以直接在可视化树中查找它。
我已经修改了您的FindVisualChild
方法，以便按名称搜索元素。为了方便起见，我还将其转换为一种扩展方法：
扩展方法
public static class Utils
{
public static bool TryFindVisualChildByName<TChild>(
this DependencyObject parent,
string childElementName,
out TChild childElement,
bool isCaseSensitive = false)
where TChild : FrameworkElement
{
childElement = null;
// Popup.Child content is not part of the visual tree.
// To prevent traversal from breaking when parent is a Popup,
// we need to explicitly extract the content.
if (parent is Popup popup)
{
parent = popup.Child;
}
if (parent == null)
{
return false;
}
var stringComparison = isCaseSensitive
? StringComparison.Ordinal
: StringComparison.OrdinalIgnoreCase;
for (int i = 0; i < VisualTreeHelper.GetChildrenCount(parent); i++)
{
DependencyObject child = VisualTreeHelper.GetChild(parent, i);
if (child is TChild resultElement
&& resultElement.Name.Equals(childElementName, stringComparison))
{
childElement = resultElement;
return true;
}
if (child.TryFindVisualChildByName(childElementName, out childElement))
{
return true;
}
}
return false;
}
}
FindVisualChild
不可能返回一个Label
实例FindVisualChild
将结果强制转换为ContentPresenter
。由于Label
不是ContentPresenter
，这将引发InvalidCastException
。但在此之前，child is childItem
将返回false
，前提是child
类型为Label
，通用参数类型childItem
类型为ContentPresenter
，因此返回一个潜在的null
短版
访问数据模板
或查找控件以获取其绑定数据总是太复杂。访问d总是比较容易