如何实现 chained/proxied 数据绑定

Question

我在我的 mvvm wpf 应用程序中遇到了这个问题，我想在其中创建 proxied/chained 数据绑定。

我的 ModelViewController 看起来像这样：

public class ListViewModel
{
    public ObservableCollection<Contact> GridData { get; private set; }
    public ObservableCollection<Contact> SelectedEntities { get; private set; }
    public bool IsSingeselect { get { return SelectedEntities.Count == 1; } }
    public bool IsMultiSelect { get { return SelectedEntities.Count > 0; } }
    public ObservableCollection<MenuComandModel> ContextMenuItems { get; private set; }
}

GridData 和 SelectedEntities 绑定到数据网格并且工作起来很有魅力。我正在使用 ContextMenuItems 集合为数据网格上下文菜单创建 BarButtonItems，这非常有效。 MenuComandModel class 有一个 Enabled 属性，我想将它绑定到 IsSingeselect 或 IsMultiSelect 属性到 BarButtonItems 成员 IsEnabled。我该如何存档？

Answer 1

由于您使用的是 DevExpress，因此您可以享受 DevExpress MVVM Framework and their POCO-ViewModels 的所有优势：

using DevExpress.Mvvm.POCO;
//...
public class ListViewModel {
    public ObservableCollection<Contact> GridData { get; private set; }

    // mark the SelectedEntities property as virtual to be notified on initializing/replacing
    public virtual ObservableCollection<Contact> SelectedEntities { get; private set; }
    // unsubscribe the CollectionChanged event in changing-callback
    protected void OnSelectedEntitiesChanging() {
        if(SelectedEntities != null)
            SelectedEntities.CollectionChanged -= SelectedEntities_CollectionChanged;
    }
    // subscribe the CollectionChanged event in changed-callback
    protected void OnSelectedEntitiesChanged() {
        if(SelectedEntities != null)
            SelectedEntities.CollectionChanged += SelectedEntities_CollectionChanged;
        UpdateSelectedEntitiesDependencies();
    }
    void UpdateSelectedEntitiesDependencies() {
        // Raise INPC for dependent properties
        this.RaisePropertyChanged(x => x.IsSingeselect);
        this.RaisePropertyChanged(x => x.IsMultiSelect);
        // Raise INPC for dependent properties of child ViewModels
        foreach(var item in ContextMenuItems)
            item.RaisePropertyChanged(x => x.Enabled);
    }
    void SelectedEntities_CollectionChanged(object sender, System.Collections.Specialized.NotifyCollectionChangedEventArgs e) {
        if(e.Action == NotifyCollectionChangedAction.Add || e.Action == NotifyCollectionChangedAction.Remove || e.Action == NotifyCollectionChangedAction.Reset)
            UpdateSelectedEntitiesDependencies();
    }
    public bool IsSingeselect { get { return SelectedEntities.Count == 1; } }
    public bool IsMultiSelect { get { return SelectedEntities.Count > 0; } }
    public ObservableCollection<MenuComandViewModel> ContextMenuItems { get; private set; }
}

public class MenuComandViewModel {
    public bool Enabled {
        get {
            var parentViewModel = this.GetParentViewModel<ListViewModel>();
            return parentViewModel.IsMultiSelect; // Some implementation
        }
    }
}

然后您可以使用MVVM Support in DXBars, DXRibbon and GalleryControl帮助文章中描述的方法绑定您禁止的项目到 ContextMenuItems 集合。

如何实现 chained/proxied 数据绑定

How to implement chained/proxied databindings

c#

data-binding

wpf

devexpress

mvvm