Question

我想在遵守MVVM的同时从ObservableCollection中删除一个项目。我理解这个任务，我认为我很好地理解了逻辑并实现了它，但是视图中的项目永远不会被删除。

我已使用断点跟踪应用程序，并正确读取selectedProject的值。我还添加了变量来检查remove语句之前和之后的Collection大小，它们是相同的值，因此它不会删除该项。我的问题是为什么？我错过了什么？我没有遵守哪些规则？对.NET来说很陌生。

**我正在使用WCF服务，从我的CodeFirst DB返回一个ObservableCollection项目，一旦用户打开Projects视图就会调用它。

查看

<ListBox ItemsSource="{Binding ProjectList, UpdateSourceTrigger=PropertyChanged}" SelectedItem="{Binding SelectedProject}" SelectedIndex="{Binding ProjectIndex}" BorderThickness="0" Margin="60,195,218.8,212.4">
        <ListBox.ItemTemplate>
            <DataTemplate>
                <TextBlock Text="{Binding ProjectName}"/>
            </DataTemplate>
        </ListBox.ItemTemplate>
    </ListBox>
    <Button Command="{Binding DeleteCommand}" Content="Up" HorizontalAlignment="Left" Margin="563,195,0,0" VerticalAlignment="Top" Height="35" Width="75"/>

视图模型

private ObservableCollection<Project> _projectList;
public ObservableCollection<Project> ProjectList
    {
        get 
        {
            var q = client.ReturnProjects().ToList();
            _projectList = new ObservableCollection<Project>(q.ToList());
            return _projectList;
        }
        set
        {
            _projectList = value;
            OnPropertyChanged("ProjectList");
        }

public int SelectedProject
    {
        get { return _selectedProject; }
        set
        {
            _selectedProject = value;
            OnPropertyChanged("SelectedProject");
        }
    }

该命令执行的方法如下，命令命中，方法调用。

public void DeleteProject()
        {

            if (SelectedProject != null)
            {
                ProjectList.Remove(SelectedProject);
            }
        }

Answer 1

您需要对SelectedItem属性进行双向绑定。

查看

    <ListBox ItemsSource="{Binding ProjectList}"
             SelectedItem="{Binding SelectedProject, Mode=TwoWay}">
        <ListBox.ItemTemplate>
            <DataTemplate>
                <TextBlock Text="{Binding Name}" />
            </DataTemplate>
        </ListBox.ItemTemplate>
    </ListBox>
    <Button Command="{Binding DeleteCommand}"
            Content="Delete"
            HorizontalAlignment="Right"
            VerticalAlignment="Bottom" />

ViewModel，模型和ICommand实现

public class ViewModel : INotifyPropertyChanged
{
    public ViewModel()
    {
        var q = new[] { new Project() { Name = "A" }, new Project() { Name = "B" }, new Project() { Name = "C" } };
        ProjectList = new ObservableCollection<Project>(q);
    }

    private ObservableCollection<Project> _projectList;

    public ObservableCollection<Project> ProjectList
    {
        get
        {
            return _projectList;
        }
        set
        {
            _projectList = value;
            OnPropertyChanged("ProjectList");
        }
    }

    Project _selectedProject;
    public Project SelectedProject
    {
        get { return _selectedProject; }
        set
        {
            _selectedProject = value;
            OnPropertyChanged("SelectedProject");
        }
    }

    public ICommand DeleteCommand => new SimpleCommand(DeleteProject);

    private void DeleteProject()
    {

        if (SelectedProject != null)
        {
            ProjectList.Remove(SelectedProject);
        }
    }
    public event PropertyChangedEventHandler PropertyChanged;
    private void OnPropertyChanged(string propertyName)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }
}

public class Project
{
    public string Name { get; set; }
}

public class SimpleCommand : ICommand
{
    Action _execute;
    public SimpleCommand(Action execute)
    {
        this._execute = execute;
    }

    public event EventHandler CanExecuteChanged;

    public bool CanExecute(object parameter) => true;

    public void Execute(object parameter)
    {
        _execute();
    }
}

Answer 2

我认为在删除项目后需要调用OnPropertyChanged（＆＃34; ProjectList＆＃34;）来引发更新视图的通知。

Answer 3

ObservableCollection必须与模型层交互。也许你需要这个： https://blogs.msdn.microsoft.com/bethmassi/2009/05/08/using-the-wpf-observablecollection-with-ef-entities/

使用MVVM从ObservableCollection中删除selectedItem

3 个答案: