WPF，为什么将PropertyChanged 添加到List<> 没有生效？

Question

为什么 PropertyChangedEvent 可以添加到 String 属性，但不能添加到 List<> 属性？

xaml 喜欢这个：

<StackPanel>
    <ListBox ItemsSource="{Binding Items}" Height="300"/>
    <Button Click="Button_Click">Change</Button>
</StackPanel>

和 xaml.cs 这样的：

public partial class MainWindow : Window, INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    //public ObservableCollection<String> Items { get; set; } = new ObservableCollection<String>(); // ok
    public List<String> Items  // no effect
    {
        get { return _items; }
        set
        {
            _items = value;
            if (PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs("Items"));
        }
    }
    private List<String> _items = new List<string>();

    public MainWindow()
    {
        InitializeComponent();
        this.DataContext = this;
        Items.Add("aaa");
        Items.Add("bbb");
    }

    private void Button_Click(object sender, RoutedEventArgs e)
    {
        Items.Clear();
        for (int i = 0; i < 5; i++)
            Items.Add(i.ToString());
     }
}

Answer 1

您的问题可以通过多种方式解决，

点击按钮创建另一个列表，示例代码如下

使用 Observable 集合

改变

    private RelayCommand _buttonClick;
     public RelayCommand ButtonClick => _buttonClick ?? new RelayCommand(onButtonClick, canButtonClick);

 private bool canButtonClick(object obj)
 {
     return true;
 }

 private void onButtonClick(object obj)
 {
     List<String> tempItems = new List<string>();
     for (int i = 0; i < 5; i++)
         tempItems.Add(i.ToString());
     Items = tempItems;
 }

Answer 2

它不起作用，因为您只在设置整个列表时通知，而不是在列表中添加或删除项目时通知。

使用 ObservableCollection<string> 而不是 List<string>:

public partial class MainWindow : Window, INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    private ObservableCollection<string> _Items = new ObservableCollection<string>();
    public ObservableCollection<string> Items
    {
        get { return _Items; }
        set
        {
            _Items = value;
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(nameof(Items));
        }
    }

    public MainWindow()
    {
        InitializeComponent();
        this.DataContext = this;
        Items.Add("aaa");
        Items.Add("bbb");
    }

    private void Button_Click(object sender, RoutedEventArgs e)
    {
        Items.Clear();
        for (int i = 0; i < 5; i++)
            Items.Add(i.ToString());
     }
}

WPF，为什么将PropertyChanged 添加到List<> 没有生效？

WPF, why adding PropertyChanged to List<> does not take into effect?

wpf

list

propertychanged