定义了一个依赖属性(类型是列表)，修改其中某项值后怎么被这个依赖属性感知到？

[tonylll]

我有一个usercontrol，定义了一个依赖属性MyText，类型是ObservableCollection<string>，但是我修改里面某一项的内容后，没法触发MyText的SetValue，也就是MyText无法感知到列表里的某项已经改变了。请问怎么才能修改数值后自动触发呢？谢谢

 

1.uc.xaml：

<UserControl x:Class="Test.uc"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             xmlns:local="clr-namespace:Test"
             mc:Ignorable="d" d:DesignHeight="100" d:DesignWidth="100">
    <Grid>
        <ContentControl x:Name="lbl"/>
    </Grid>
</UserControl>

2.uc.xaml.cs

using System;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Windows;
using System.Windows.Controls;

namespace Test
{
    public partial class uc : UserControl
    {
        public static readonly DependencyProperty MyTextProperty =
                    DependencyProperty.Register("MyText", typeof(ObservableCollection<string>), typeof(uc), new PropertyMetadata(new ObservableCollection<string>()));

        [Bindable(true)]
        public ObservableCollection<string> MyText
        {
            get { return (ObservableCollection<string>)GetValue(MyTextProperty); }
            set {
                SetValue(MyTextProperty, value);
                ObservableCollection<string> lst = value as ObservableCollection<string>;
                string s = "";
                foreach (string item in lst) s += item;
                lbl.Content = s;
            }
        }

        public uc()
        {
            InitializeComponent();
            this.DataContext = this;
        }
    }
}

3.MainWindow.xaml

<Window x:Class="Test.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:Test"
        mc:Ignorable="d" Height="100" Width="200">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="30"/>
            <RowDefinition Height="30"/>
        </Grid.RowDefinitions>
        <local:uc x:Name="uc" MyText="{Binding list}" Grid.Row="0"/>
        <Button x:Name="btn" Grid.Row="1" Click="btn_Click"/>
    </Grid>
</Window>

4.MainWindow.xaml.cs

using System.Collections.ObjectModel;
using System.Windows;

namespace Test
{
    public partial class MainWindow : Window
    {
        public ObservableCollection<string> list { get; set; } = new ObservableCollection<string>();
        public MainWindow()
        {
            InitializeComponent();
            list.Add("a"); list.Add("b");
            uc.MyText = this.list;
        }

        private void btn_Click(object sender, RoutedEventArgs e)
        {
            list[1] = "c";
            uc.MyText = this.list;//必须要加这句强制赋值，界面的标签才会变成ac，注释掉这行后uc就无法感知到？
        }
    }
}