WPF将列表框 itemtemplate 内的绑定到 ObservableCollection 源源 PropertyChanged 被忽略

问题描述

我正在尝试创建一个显示格式化文本的列表框。我希望能够从代码中更改格式。

为了显示格式化文本，我选择了 TextBlock 并打算使用 TextBlock.Inlines 集合进行格式化。 TextBlock.Inlines 是不可绑定的，所以我创建了从 TextBlock 派生的新类 BindableTextBlock。这个类有一个依赖属性 InlineList，我试图将它绑定到模型中的 InlinesColl ObservableCollection。

问题是 InlinesColl 中的更改不会通知我的 InlineList 关于 PropertyChanged 事件。绑定仅在 BindableTextBlock 对象创建时运行一次，以后再也不运行了。

知道为什么吗？

XAML：

                <ListBox  x:Name="PART_lb" VerticalAlignment="Stretch" ItemsSource="{Binding ItemColl}"
                            ScrollViewer.HorizontalScrollBarVisibility="Auto" 
                            ScrollViewer.VerticalScrollBarVisibility="Auto" >
                    
                    <ListBox.ItemTemplate>
                        <DataTemplate>
                            <local:BindableTextBlock InlineList="{Binding Path=InlinesColl}" />
                        </DataTemplate>
                    </ListBox.ItemTemplate>
                    
                </ListBox>

BindableTextBlock 类：

 public class BindableTextBlock : TextBlock
    {
        public ObservableCollection<Inline> InlineList
        {
            get { return (ObservableCollection<Inline>)GetValue(InlineListProperty); }
            set { SetValue(InlineListProperty,value); }
        }

        public static readonly DependencyProperty InlineListProperty =
            DependencyProperty.Register("InlineList",typeof(ObservableCollection<Inline>),typeof(BindableTextBlock),new UIPropertyMetadata(null,OnPropertyChanged));

        private static void OnPropertyChanged(DependencyObject sender,DependencyPropertyChangedEventArgs e)
        {
            BindableTextBlock textBlock = (BindableTextBlock)sender;
            textBlock.Inlines.Clear();
            textBlock.Inlines.AddRange((ObservableCollection<Inline>)e.NewValue);
        }

      
    }

模型类

    public class TextBlockModel
    {

        ObservableCollection<Inline> _inlinesColl = new ObservableCollection<Inline>();
        public ObservableCollection<Inline> InlinesColl
        {
            get { return _inlinesColl; }
            set {_inlinesColl = value; }
        }
    }

带有 ListBox ItemSource 集合的 ViewModel

        ObservableCollection<TextBlockModel> _itemColl = new ObservableCollection<TextBlockModel>();
        public ObservableCollection<TextBlockModel> ItemColl
        {
            get { return _itemColl; }
            set { _itemColl = value; }
        }

测试项目here

解决方法

在你的情况下 - 当集合中的项目被添加\删除时，你没有处理案例
需要深入了解并在分配新集合时订阅 CollectionChanged。

 public class BindableTextBlock : TextBlock
    {
        static int Cntr = 0;
        public BindableTextBlock()
        {
            Console.WriteLine("BindableTextBlock constructor " + Cntr);
            Cntr++;
        }

        public ObservableCollection<Inline> InlineList
        {
            get { return (ObservableCollection<Inline>)GetValue(InlineListProperty); }
            set { SetValue(InlineListProperty,value); }
        }

        public static readonly DependencyProperty InlineListProperty =
            DependencyProperty.Register("InlineList",typeof(ObservableCollection<Inline>),typeof(BindableTextBlock),new UIPropertyMetadata(null,OnPropertyChanged));

        private static void OnPropertyChanged(DependencyObject sender,DependencyPropertyChangedEventArgs e)
        {
            BindableTextBlock textBlock = (BindableTextBlock)sender;

            // subscribe to collection changed
            textBlock.UpdateInlineListSource((ObservableCollection < Inline > )e.OldValue,(ObservableCollection < Inline > )e.NewValue);

        }

        public void UpdateInlineListSource(ObservableCollection<Inline> oldCollection,ObservableCollection<Inline> newCollection)
        {
            if (oldCollection!=null)
            oldCollection.CollectionChanged -= OnCollectionChanged;

            if (newCollection != null)
            {
                newCollection.CollectionChanged += OnCollectionChanged;
                OnCollectionChanged(this,new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset));
                OnCollectionChanged(this,new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Add,newCollection));
            }
        }

        private void OnCollectionChanged(object sender,System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
        {
            var newItems = e.NewItems?.Cast<Inline>()?.ToList() ?? new List<Inline>();
            var oldItems = e.OldItems?.Cast<Inline>()?.ToList() ?? new List<Inline>();

            // changed source
            if (e.Action==NotifyCollectionChangedAction.Reset)
                this.Inlines.Clear();

            foreach (var itemForDelete in oldItems)
            {
                if (this.Inlines.Contains(itemForDelete))
                    this.Inlines.Remove(itemForDelete);
            }

            foreach (var itemsForAdd in newItems)
            {
                this.Inlines.Add(itemsForAdd);
            }
        }
    }