OnPropertyChanged 不更新视图

Question

我有一个 ListView，它的项目源是 Elements，它是一个 Schranken 对象列表。 SchrankePresenter 是页面的 DataContext（在构造函数中设置）。

页面正确显示，直到单击一个按钮。如果单击一个按钮，按钮的名称值应该改变，ListView 应该多一个项目，但什么都没有 happens/updates。

这是 SchrankenPresenter：

 public class SchrankePresenter : INotifyPropertyChanged
    {
        private List<Schranke> _elements;
        public List<Schranke> Elements
        {
            get { return _elements; }
            set
            {
                _elements = value;
                OnPropertyChanged("Elements");
            }
        }
        public ICommand ClickCommand { get; set; }
    private void OnPropertyChanged(string propName)
    {
        Debug.WriteLine($"on Property changed with {propName}");
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propName));
    }

    public event PropertyChangedEventHandler PropertyChanged;

    public SchrankePresenter()
    {
        var elements = new List<Schranke>();
        for (var i = 1; i < 15; i++)
            elements.Add(new Schranke() { Name = $"{i}: Schranke" });

        Elements = elements;
        Debug.WriteLine("ctor");
        ClickCommand = new DelegateCommand<Schranke>(ClickAction);
    }

    public void ClickAction(Schranke item)
    {
        VibrationDevice.GetDefault().Vibrate(TimeSpan.FromMilliseconds(150));

        Debug.WriteLine($"{item?.Name} was clicked");
        item.Name = "was clicked";
        OnPropertyChanged("Name");
        Elements.Add(new Schranke() { Name = "addednew element" });
        OnPropertyChanged("Elements");

    }

}

class Schranke 只有一名成员：public string Name { get; set; }

视图看起来像：

 <ListView ItemsSource="{Binding Elements, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" x:Name="lv_schranken" Grid.Row="1" SelectedItem="{Binding  SelectedItem}">

            <ListView.ItemTemplate>
                <DataTemplate>
                    <Button Height="80"
                            HorizontalAlignment="Stretch"
                            Command="{Binding ElementName=lv_schranken, Path=DataContext.ClickCommand}"
                            CommandParameter="{Binding}"
                            Style="{StaticResource TransparentStyle}">
                        <Grid>
                                .
                                .  (some grid stuff)
                                .

                            <TextBlock Name="schranken_name"
                                       Grid.Row="1"
                                       Grid.Column="1"
                                       HorizontalAlignment="Center"
                                       VerticalAlignment="Center"
                                       FontWeight="ExtraLight"
                                       FontSize="25"
                                       Foreground="Black"
                                       Text="{Binding Name, Mode=TwoWay}" />
                        </Grid>
                    </Button>
                </DataTemplate>

            </ListView.ItemTemplate>

        </ListView>

PS：如果有人需要 DelegateCommand - 实现：

 public class DelegateCommand<T> : ICommand
    {
    private Action<T> _clickAction;

    public DelegateCommand(Action<T> clickAction)
    {
        _clickAction = clickAction;
    }

    public event EventHandler CanExecuteChanged;

    public bool CanExecute(object parameter)
    {
        return true;
    }

    public void Execute(object parameter)
    {
        _clickAction((T)parameter);
    }
}

Answer 1

如果你想绑定到项目列表，你应该绑定到 ObservableCollection:

Represents a dynamic data collection that provides notifications when items get added, removed, or when the whole list is refreshed.

https://msdn.microsoft.com/de-de/library/ms668604(v=vs.110).aspx

Answer 2

为了从 Viewmodel 更新 UI，我们需要提出 inotifypropertychanged； observablecollection 默认提供 inotifypropertychanged 实现； .

我们可以参考 observablecollection

如果你想使用相同的列表，那么你需要在那个特定的列表上实现inotifypropertychanged

OnPropertyChanged 不更新视图

OnPropertyChanged does not update the View

data-binding

wpf

xaml

inotifypropertychanged