在ItemContainerGenerator上找不到子控件吗？

Question

我将ItemsControl用于StackPanel，如下代码所示：

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等于空，

我已经搜索并阅读了更多关于这方面的内容，但我不知道如何解决它。

Answer 1

我创建了一个演示来测试这个，但它对我有效。在所有可用访问的情况下，都会触发加载事件，因此我从未遇到实例为null的状态。

然而，我有一种感觉，你还没有告诉我们你到底在做什么。

您是否在运行时更改ItemsSource？您在什么时候交换ItemsSource？

您的下列代码在哪里被调用？

channelBtnItems.ItemContainerGenerator.StatusChanged += ChannelBtnItemsStatusChangedEventHandler;
channelBtnItems.ItemsSource = listChannelBtnItemData;
channelBtnItems.Items.Refresh();

然而，这里有一个技巧，你可以“推迟”一个行动。

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，请提供完整的代码，包括数据和视图模型，以便可以测试相同的代码，就像你的。