需要一个使用 MVVM 级联组合框的简单示例 [英] Need a simple Example of cascading combo boxes using MVVM

问题描述

需要一个使用 MVVM 的级联组合框的简单示例

Need a simple Example of cascading combo boxes using MVVM

Wpf/Silverlight

Wpf / Silverlight

推荐答案

如果我理解您的问题，您希望下一个组合框根据前一个值填充数据.

If I understand your question you want to have the next combobox to fill with data based on the previous value.

我有一个通用的 ViewModel，您可以使用它来捕获项目列表和所选项目

I have a generic ViewModel that you can have to capture the list of items and the selected item

class ItemListViewModel<T> : INotifyPropertyChanged where T : class
{
    private T _item;
    private ObservableCollection<T> _items;

    public ItemListViewModel()
    {
        _items = new ObservableCollection<T>();
        _item = null;
    }

    public void SetItems(IEnumerable<T> items)
    {
        Items = new ObservableCollection<T>(items);
        SelectedItem = null; 
    }

    public ObservableCollection<T> Items
    {
        get { return _items; }
        private set
        {
            _items = value;
            RaisePropertyChanged("Items");
        }
    }

    public T SelectedItem
    {
        get { return _item; }
        set
        {
            _item = value;
            RaisePropertyChanged("SelectedItem");
        }
    }

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

然后拥有将绑定到视图的 DataContext 的主视图模型.让 Load 方法做你想做的事

Then have the main viewmodel that will be bound to the DataContext of the view. Have the Load methods do what you want

class MyViewModel : INotifyPropertyChanged
{
    public MyViewModel()
    {
        First = new ItemListViewModel<string>();
        Second = new ItemListViewModel<string>();
        Third = new ItemListViewModel<string>();

        First.PropertyChanged += (s, e) => Update(e.PropertyName, First, Second, LoadSecond);
        Second.PropertyChanged += (s, e) => Update(e.PropertyName, Second, Third, LoadThird);

        LoadFirst();
    }

    public ItemListViewModel<string> First { get; set; }
    public ItemListViewModel<string> Second { get; set; }
    public ItemListViewModel<string> Third { get; set; }

    private void LoadFirst()
    {
        First.SetItems(new List<string> { "One", "Two", "Three" });
    }
    private void LoadSecond()
    {
        Second.SetItems(new List<string> { "First", "Second", "Third" });
    }
    private void LoadThird()
    {
         Third.SetItems(new List<string> { "Firsty", "Secondly", "Thirdly" });
    }

    private void Update<T0, T1>(string propertyName, ItemListViewModel<T0> parent, ItemListViewModel<T1> child, Action loadAction)
        where T0 : class
        where T1 : class
    {
        if (propertyName == "SelectedItem")
        {
            if (parent.SelectedItem == null)
            {
                child.SetItems(Enumerable.Empty<T1>());
            }
            else
            {
                loadAction();
            }
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;
}

在你看来，在某处有这段代码.

And in your view have this code somewhere.

    <ComboBox ItemsSource="{Binding First.Items}" SelectedItem="{Binding First.SelectedItem}" />
    <ComboBox ItemsSource="{Binding Second.Items}" SelectedItem="{Binding Second.SelectedItem}" />
    <ComboBox ItemsSource="{Binding Third.Items}" SelectedItem="{Binding Third.SelectedItem}" />

您可以重构以使其更好，使用 MVVM 框架或派生专门用于项目列表的 ItemListViewModel 并在其中加载以更好地封装.由你决定.

You can refactor to make it nicer, use MVVM frameworks or derive the ItemListViewModel specifically for the list of items and have the load in there for better encapsulation. Its up to you.

如果任何父组合框值发生更改，则所有子列表都将被清除.

If any parent combobox value gets changed then all child lists will get cleared.

HTH

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