[英]Why does a string INotifyPropertyChanged property update but not a List<string>?
在下面的WPF應用程序中,當您單擊該按鈕時,為什么TheTitle TextBlock會更新但FilesCopied ListBox不會更新?
XAML:
<Window x:Class="TestList3433.Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="Window1" Height="300" Width="300">
<StackPanel>
<TextBlock Text="{Binding TheTitle}"/>
<TextBlock Text="above"/>
<ListBox ItemsSource="{Binding FilesCopied}"/>
<TextBlock Text="below"/>
<Button Content="Add to collection" Click="Button_Click"/>
</StackPanel>
</Window>
后台代碼:
using System.Collections.Generic;
using System.Windows;
using System.ComponentModel;
namespace TestList3433
{
public partial class Window1 : Window, INotifyPropertyChanged
{
#region ViewModelProperty: FilesCopied
private List<string> _filesCopied = new List<string>();
public List<string> FilesCopied
{
get
{
return _filesCopied;
}
set
{
_filesCopied = value;
OnPropertyChanged("FilesCopied");
}
}
#endregion
#region ViewModelProperty: TheTitle
private string _theTitle;
public string TheTitle
{
get
{
return _theTitle;
}
set
{
_theTitle = value;
OnPropertyChanged("TheTitle");
}
}
#endregion
public Window1()
{
InitializeComponent();
DataContext = this;
FilesCopied.Add("test1.txt");
TheTitle = "This is the title";
}
private void Button_Click(object sender, RoutedEventArgs e)
{
FilesCopied.Add("test2.txt");
TheTitle = "title was changed";
}
#region INotifiedProperty Block
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string propertyName)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(propertyName));
}
}
#endregion
}
}
謝謝Robert,我忘記了ObservableCollection。 這是答案:
將FilesCopied塊更改為:
#region ViewModelProperty: FilesCopied
private ObservableCollection<string> _filesCopied = new ObservableCollection<string>();
public ObservableCollection<string> FilesCopied
{
get
{
return _filesCopied;
}
set
{
_filesCopied = value;
OnPropertyChanged("FilesCopied");
}
}
#endregion
並添加:
using System.Collections.ObjectModel;
您的更改處理程序位於列表的setter中; 但您沒有調用 setter(更改列表) - 您正在向現有列表添加項目。 有單獨的接口( IBindingList
/ IBindingListView
等)用於處理列表通知。 BindingList<T>
是具有通知支持的2.0列表的合理默認實現。
在.NET 3.0及更高版本中,另請參見INotifyCollectionChanged
和ObservableCollection<T>
IMO:
private readonly ObservableCollection<string> filesCopied =
new ObservableCollection<string>();
public ObservableCollection<string> FilesCopied {
get { return filesCopied; }
}
因為它沒有實現IBindingList(View),因此UI永遠不會知道你在列表中添加任何新內容。
使用BindingList或ObservableCollection。
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