从列表框中获取选中的项目

Question

我刚刚开始习惯 MVVM 并且想要在没有代码隐藏的情况下进行操作并在视图模型中定义所有内容。组合框代表几个选择选项（作品）。我想查询已检查的元素。不幸的是我无法访问它们。文本框应将所有选定元素显示为串联字符串。

视图模型

class MainViewModel : BaseViewModel
    {
        #region Fields

        private ObservableCollection<EssayTypeViewModel> _essayTypes;
        private EssayTypeViewModel _selectedEssayTypes;

        #endregion


        public ObservableCollection<EssayTypeViewModel> EssayTypes
        {
            get => _essayTypes;
            set
            {
                if (_essayTypes == value) return;
                _essayTypes = value; OnPropertyChanged("EssayTypes");
            }
        }


        public EssayTypeViewModel SelectedEssayTypes
        {
            get => _selectedEssayTypes;
            set { _selectedEssayTypes = value; OnPropertyChanged("SelectedEssayTypes"); }
        }


        public MainViewModel()
        {

            // Load Essay Types
            EssayTypeRepository essayTypeRepository = new EssayTypeRepository();
            var essayTypes = essayTypeRepository.GetEssayTypes();
            var essayTypeViewModels = essayTypes.Select(m => new EssayTypeViewModel()
            {
                Text = m.Text
            });

            EssayTypes = new ObservableCollection<EssayTypeViewModel>(essayTypeViewModels);

        }
    }

XAML

<ListBox x:Name="Listitems" SelectionMode="Multiple" Height="75" Width="200" ItemsSource="{Binding EssayTypes}" >
        <ListBox.ItemTemplate>
            <DataTemplate>
                <CheckBox Content="{Binding Text}" IsChecked="{Binding Checked}"/>
            </DataTemplate>
        </ListBox.ItemTemplate>
    </ListBox>

    <TextBox Text="{Binding Path=SelectedEssayTypes}" Grid.Column="0" Width="160" Height="25" Margin="0,140,0,0"/>

Answer 1

您可以在复选框绑定上应用 Mode = Two 方式。

<CheckBox Content="{Binding Text}" IsChecked="{Binding Checked, Mode=TwoWay}"/>

然后您可以遍历论文类型集合以检查条目条目是否被选中。

例如。示例代码可以是：

foreach (var essayTypeInstance in EssayTypes)
{
     if(essayTypeInstance.Checked)
     {
          // this value is selected
     }
}

希望对您有所帮助。

Answer 2

您可以将事件处理程序连接到 EssayTypes 集合中所有 EssayTypeViewModel 对象的 PropertyChanged 事件，并引发只读的 PropertyChanged 事件属性的 MainViewModel 即 returns 所有选定的元素作为连接字符串：

public MainViewModel()
{
    // Load Essay Types
    EssayTypeRepository essayTypeRepository = new EssayTypeRepository();
    var essayTypes = essayTypeRepository.GetEssayTypes();
    var essayTypeViewModels = essayTypes.Select(m =>
    {
        var vm = EssayTypeViewModel()
        {
            Text = m.Text
        };
        vm.PropertyChanged += OnPropertyChanged;
        return vm;
    });

    EssayTypes = new ObservableCollection<EssayTypeViewModel>(essayTypeViewModels);
}

private void OnPropertyChanged(object sender, PropertyChangedEventArgs e)
{
    if (e.PropertyName == "Checked")
        OnPropertyChanged("SelectedItems");
}

public string SelectedItems => string.Join(",", EssayTypes.Where(x => x.Checked).ToArray());

这需要 EssayTypeViewModel class 实现 INotifyPropertyChanged 接口（例如从您的 BaseViewModel class 派生）。

Answer 3

mm8 答案有效。与此同时，我想出了另一种方法。不是 100% MVVM 兼容，但它可以工作并且非常简单。

XAML

<ListBox x:Name="ListItems" SelectionMode="Multiple" Height="75" Width="200" ItemsSource="{Binding CollectionOfItems}" >
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <CheckBox Content="{Binding Name}" IsChecked="{Binding Checked, Mode=TwoWay}" Unchecked="GetCheckedElements" Checked="GetCheckedElements" />
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>

        <TextBox Text="{Binding SelectedItemsString, UpdateSourceTrigger=PropertyChanged}" Grid.Column="0" Width="160" Height="25" Margin="0,140,0,0"/>

代码隐藏

public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            DataContext = new MainViewModel();
        }


        private void GetCheckedElements(object sender, RoutedEventArgs e)
        {
            (DataContext as MainViewModel)?.FindCheckedItems();
            (DataContext as MainViewModel)?.ConcatSelectedElements();
        }

    }

型号

public class Items
    {
        public bool Checked { get; set; }
        public string Name { get; set; }

    }

ItemsViewModel（BaseViewModel 仅实现 INotifyPropertyChanged）

class ItemsViewModel : BaseViewModel
    {
        private bool _checked;
        private string _name;

        public bool Checked
        {
            get => _checked;
            set
            {
                if (value == _checked) return;

                _checked = value;
                OnPropertyChanged("Checked");
            }
        }

        public string Name
        {
            get => _name;
            set
            {
                if (value == _name) return;

                _name = value;
                OnPropertyChanged("Name");
            }
        }
    }

MainViewModel

public class MainViewModel : BaseViewModel
    {
        private string _selectedItemsString;
        private ObservableCollection<Items> _selectedItems;



        public ObservableCollection<Items> CollectionOfItems { get; set; }

        public ObservableCollection<Items> SelectedItems
        {
            get => _selectedItems;
            set
            {
                _selectedItems = value;
                OnPropertyChanged("SelectedItems");
            } 
        }


        public string SelectedItemsString
        {
            get => _selectedItemsString;
            set
            {
                if (value == _selectedItemsString) return;

                _selectedItemsString = value;
                OnPropertyChanged("SelectedItemsString");
            }
        }

        public MainViewModel()
        {
            CollectionOfItems = new ObservableCollection<Items>();
            SelectedItems = new ObservableCollection<Items>();




            CollectionOfItems.Add(new Items { Checked = false, Name = "Item 1" });
            CollectionOfItems.Add(new Items { Checked = false, Name = "Item 2" });
            CollectionOfItems.Add(new Items { Checked = false, Name = "Item 3" });

        }


        public void FindCheckedItems()
        {
            CollectionOfItems.Where(x => x.Checked).ToList().ForEach(y => SelectedItems.Add(y));
        }


        public void ConcatSelectedElements()
        {
            SelectedItemsString = string.Join(", ", CollectionOfItems.Where(x => x.Checked).ToList().Select(x => x.Name)).Trim();
        }
    }

从列表框中获取选中的项目

Get checked items from a listbox

c#

wpf

checkbox

mvvm

viewmodel