绑定到列表框 ui 的 ObservableCollection 不更新

Question

我知道我应该使用 MVVM 模式，但我正在努力逐步接近它。所以这是我的列表框：

<ListBox x:Name="BoardList" ItemsSource="{Binding notes}" >
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <Grid>
                        <StackPanel Orientation="Horizontal" HorizontalAlignment="Right">
                            <TextBox IsReadOnly="True" ScrollViewer.VerticalScrollBarVisibility="Visible" Text="{Binding text}" TextWrapping="Wrap" Foreground="DarkBlue"></TextBox>
                            <AppBarButton Visibility="{Binding visibility}" Icon="Globe" Click="OpenInBrowser" x:Name="Link"></AppBarButton>
                            <AppBarButton Icon="Copy" Click="Copy"></AppBarButton>
                            <AppBarButton Icon="Delete" Click="Delete"></AppBarButton>
                        </StackPanel>
                    </Grid>
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>

在 Mainpage.xaml.cs 我声明如下：

    ObservableCollection<BoardNote> notes   = new ObservableCollection<BoardNote>();

所以，如果我理解正确，我就不需要关心 "INotifyCollectionChanged" 的东西，因为我正在使用 observablecollection？所以我得到了一个像这样的文本框：

<Textbox x:Name="UserInputNote" Placeholdertext="Type in a text for your note"></Textbox>

还有一个添加新笔记到ObservableCollection的按钮，点击事件是这样的：

notes.Add(new BoardNote(UserInputNote.Text));

所以现在 UI 应该在用户每次单击按钮保存新笔记时更新。但是没有任何反应。我做错了什么？

如果您需要，这里是 BoardNote class:

   class BoardNote
{
    public string text
    {
        get; set;
    }
        public BoardNote(string text)
    {
        this.text = text;
    }
    public Visibility visibility
    {
        get
        {
            if (text.StartsWith("http"))
                return Visibility.Visible;
            else
                return Visibility.Collapsed;
        }
    }
}

Answer 1

您需要实施 INotifyPropertyChanged。这是一种方法。

创建此 NotificationObject class。

 public class NotificationObject : INotifyPropertyChanged
 {
    protected void RaisePropertyChanged<T>(Expression<Func<T>> action)
    {
        var propertyName = GetPropertyName(action);
        RaisePropertyChanged(propertyName);
    }

    private static string GetPropertyName<T>(Expression<Func<T>> action)
    {
        var expression = (MemberExpression)action.Body;
        var propertyName = expression.Member.Name;
        return propertyName;
    }

    private void RaisePropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
    }

    public event PropertyChangedEventHandler PropertyChanged;
}

那么你的 BoardNote class 将以这种方式继承它：

class BoardNote : NotificationObject
{
private string _text
public string Text
{
    get {return _text;}
    set 
    {
     if(_text == value) return;
     _text = value;
     RaisePropertyChanged(() => Text);
    }
}
    public BoardNote(string text)
{
    this.text = text;
}
public Visibility visibility
{
    get
    {
        if (text.StartsWith("http"))
            return Visibility.Visible;
        else
            return Visibility.Collapsed;
    }
}
}

绑定到列表框 ui 的 ObservableCollection 不更新

ObservableCollection binding to listbox ui doesn't update

c#

wpf

binding

listbox

mvvm