我正在ItemsControl使用StackPanel代码如下：
File playBackControl.xaml - Begin
<ScrollViewer x:Name="scrollViewerChannelBtns">
<StackPanel x:Name="channelBtns" Orientation="Vertical" MouseWheel="ScrollViewer_MouseWheel">
<ItemsControl x:Name="channelBtnItems" ItemsSource="{Binding}">
<ItemsControl.ItemTemplate>
<DataTemplate>
<ToogleButton x:Name="tgbChannelName"
HorizontalAlignment="Center" VerticalAlignment="Center"
Width="{Binding Path=ChannelNameBtnWidth}"
Height="{Binding Path=ChannelNameBtnHeight}"
Margin="{Binding Path=ChannelNameBtnMargin}"
IsChecked="{Binding Path=IsChecked, Mode=TwoWay}"
ToolTip="{Binding Path=ToolTip}" Tag="{Binding Path=Index}"
IsEnabled="{Binding Path=IsEnabled}" />
</DataTemplate>
</ItemsControl.ItemTemplate>
</ItemsControl>
</StackPanel>
</ScrollViewer>
File playBackControl.xaml - End
File playBackControl.xaml.cs - Begin
public partial class PlayBackControl : UserControl
{
public static List<ChannelBtnItemData> listChannelBtnItemData = new List<ChannelBtnItemData>();
public PlayBackControl() //This will run first when the app start
{
InitializeComponent();
channelBtnItems.ItemContainerGenerator.StatusChanged += ChannelBtnItemsStatusChangedEventHandler;
System.Threading.Thread threadTimer = new System.Threading.Thread(TimerThreadThreadProc);
threadTimer.Start();
}
private void TimerThreadThreadProc()
{
while (true)
{
Thread.Sleep(60000); //Sleep 60s
this.Dispatcher.BeginInvoke(new Action(delegate()
{
//Re init listChannelBtnItemData, this list has about 64 items
channelBtnItems.ItemsSource = listChannelBtnItemData;
channelBtnItems.Items.Refresh();
}));
}
}
public class ChannelBtnItemData : INotifyPropertyChanged
{
private String _toolTip;
private int _index;
private int _channelID;
private bool _isChecked;
private bool _isEnabled;
private bool _lockToggle;
private double _channelNameBtnWidth;
private double _channelNameBtnHeight;
private Thickness _channelNameBtnMargin;
public String ToolTip
{
get { return _toolTip; }
set
{
_toolTip = value;
OnPropertyChanged("ToolTip");
}
}
public int Index
{
get { return _index; }
set
{
_index = value;
OnPropertyChanged("Index");
}
}
public int ChannelID
{
get { return _channelID; }
set
{
_channelID = value;
OnPropertyChanged("ChannelID");
}
}
public bool IsChecked
{
get { return _isChecked; }
set
{
_isChecked = value;
OnPropertyChanged("IsChecked");
}
}
public bool IsEnabled
{
get { return _isEnabled; }
set
{
_isEnabled = value;
OnPropertyChanged("IsEnabled");
}
}
public bool LockToggle
{
get { return _lockToggle; }
set
{
_lockToggle = value;
OnPropertyChanged("LockToggle");
}
}
public double ChannelNameBtnWidth
{
get { return _channelNameBtnWidth; }
set
{
_channelNameBtnWidth = value;
OnPropertyChanged("ChannelNameBtnWidth");
}
}
public double ChannelNameBtnHeight
{
get { return _channelNameBtnHeight; }
set
{
_channelNameBtnHeight = value;
OnPropertyChanged("ChannelNameBtnHeight");
}
}
public Thickness ChannelNameBtnMargin
{
get { return _channelNameBtnMargin; }
set
{
_channelNameBtnMargin = value;
OnPropertyChanged("ChannelNameBtnMargin");
}
}
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged(string propertyName)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
handler(this, new PropertyChangedEventArgs(propertyName));
}
public ChannelBtnItemData()
{
}
}
private void ChannelBtnItemsStatusChangedEventHandler(Object sender, EventArgs e)
{
if (channelBtnItems.ItemContainerGenerator.Status == GeneratorStatus.ContainersGenerated)
{
if (channelBtnItems.HasItems)
{
var containers = channelBtnItems.Items.Cast<Object>().Select(
item => (FrameworkElement)channelBtnItems.ItemContainerGenerator.ContainerFromItem(item));
foreach (var container in containers)
{
if (container != null)
container.Loaded += ChannelBtnItemContainerLoaded;
}
}
}
}
private void ChannelBtnItemContainerLoaded(object sender, RoutedEventArgs e)
{
var element = (FrameworkElement)sender;
element.Loaded -= ChannelBtnItemContainerLoaded;
ToogleButton tgbChannelName = FindChild<ToogleButton>(element, "tgbChannelName");
if (tgbChannelName != null) //Sometimes It equal null
{
//Do something
}
}
public T FindChild<T>(DependencyObject parent, string childName)
where T : DependencyObject
{
// Confirm parent and childName are valid.
if (parent == null) return null;
T foundChild = null;
int childrenCount = VisualTreeHelper.GetChildrenCount(parent);
for (int i = 0; i < childrenCount; i++)
{
var child = VisualTreeHelper.GetChild(parent, i);
// If the child is not of the request child type child
T childType = child as T;
if (childType == null)
{
// recursively drill down the tree
foundChild = FindChild<T>(child, childName);
// If the child is found, break so we do not overwrite the found child.
if (foundChild != null) break;
}
else if (!string.IsNullOrEmpty(childName))
{
var frameworkElement = child as FrameworkElement;
// If the child's name is set for search
if (frameworkElement != null && frameworkElement.Name == childName)
{
// if the child's name is of the request name
foundChild = (T)child;
break;
}
else
{
// recursively drill down the tree
foundChild = FindChild<T>(child, childName);
// If the child is found, break so we do not overwrite the found child.
if (foundChild != null) break;
}
}
else
{
// child element found.
foundChild = (T)child;
break;
}
}
return foundChild;
}
}
File playBackControl.xaml.cs - End
在ChannelBtnItemContainerLoaded()函数中，有时tgbChannelName等于null，
我已经搜索并阅读了更多相关信息，但我不知道如何修复它。
答案 0 :(得分：1)
我创建了一个演示来测试它，但它对我有用。当一切都可以访问时，正在触发加载的事件，因此我从未遇到过实例为null的状态。
但是我觉得你没有透露我们你到底在那里做什么。
您是否在运行时更改ItemsSource？你什么时候交换ItemsSource？
您的以下代码在哪里被调用？
channelBtnItems.ItemContainerGenerator.StatusChanged += ChannelBtnItemsStatusChangedEventHandler;
channelBtnItems.ItemsSource = listChannelBtnItemData;
channelBtnItems.Items.Refresh();
然而，这是一个如何“推迟”行动的技巧。
将Dispatcher.BeginInvoke与DispatcherPrority.Background一起使用。
http://weblogs.asp.net/pawanmishra/archive/2010/06/06/understanding-dispatcher-in-wpf.aspx
private void ChannelBtnItemContainerLoaded(object sender, RoutedEventArgs e)
{
var element = (FrameworkElement)sender;
element.Loaded -= ChannelBtnItemContainerLoaded;
element.Dispatcher.BeginInvoke((Action)(() =>
{
ToggleButton tgbChannelName = FindChild<ToggleButton>(element, "tgbChannelName");
if (tgbChannelName != null) //Sometimes It equal null
{
//Do something
}
else
{
}
}), DispatcherPriority.Background);
}
试一试。如果这没有帮助，请向我们提供完整的代码，包括数据和视图模型，因此可以测试与您相同的代码。