[SilverLight]MVVM下绑定TreeView

文章使用的是MVVMLight框架，下载地址：http://mvvmlight.codeplex.com/

首先要对TreeView进行扩展，使得它能够有Command，里面需要用到Prism，下载地址：http://www.microsoft.com/en-us/download/details.aspx?displaylang=en&id=28950

参考文章：http://www.silverlightshow.net/items/Make-the-TreeView-control-to-be-MVVM-compliant.aspx

需要先添加引用：

xmlns:tree="clr-namespace:[your namespace]"

View代码：

<tree:TreeViewWithCommand   ItemsSource="{Binding Root,Mode=TwoWay}" 
                            tree:ItemExpanded.Command="{Binding ItemExpanded}"
                            tree:SelectedItemChanged.Command="{Binding ItemSelected}">
     <tree:TreeViewWithCommand.ItemTemplate>
          <c:HierarchicalDataTemplate ItemsSource="{Binding Children,Mode=TwoWay}"   >
                 <TextBlock Text="{Binding Current. Value,Mode=TwoWay}"></TextBlock>
          </c:HierarchicalDataTemplate>
     </tree:TreeViewWithCommand.ItemTemplate>
</tree:TreeViewWithCommand>

然后新增一个View用来存储TreeView的数据：

public class Tree<T> 
    {
        public ObservableCollection<Tree<T>> Children { get; set; }
        public T Current { get; set; }
        
        

        public Tree(T parent)
        {
            this.Current = parent;
            this.Children = new ObservableCollection<Tree<T>>();
        }

        public Tree(T parent, T child)
        {
            this.Current = parent;
            this.Children = new ObservableCollection<Tree<T>>();
            this.Children.Add(new Tree<T>(child));
        }

        
    }

public class Product
        {
            public int ProductId { get; set; }
            public string ProductName { get; set; }
        }

在ViewModel（记得继承ViewModelBase）中添加属性用来存放TreeView的数据：

private ObservableCollection<Tree<Product>> _root;
        public ObservableCollection<Tree<Product>> Root
        {
            get { return _root; }
            private set
            {
                if (!ReferenceEquals(_root, value))
                {
                    _root = value;
                    RaisePropertyChanged("Root");

                }

            }
        }

先加载父级节点，对于每个节点添加loading子节点，那样展开节点时就会先显示loading节点，当获取到数据时再加载数据：

private void LoadData()
        {
            this.Root = new ObservableCollection<Tree<Product>>();
            Root.Add(new Tree<Product>(BuildLoadingChild()));

            lstProduct = 获取数据;

            this.Root.Clear();
            foreach (Product item in lstProduct )
            {
                Root.Add(new Tree<Product>(item, BuildLoadingChild()));

            }
        }

        private Product BuildLoadingChild()
        {
            return new Product()
            {
                ProductId = -999,
                ProductName = "loading"
            };
        }

展开节点时获取子节点，当然不能忘记先要把loading节点给删掉，先在ViewModel中定义RelayCommand：

private RelayCommand<Tree<Product>> _itemExpanded;
        public RelayCommand<Tree<Product>> ItemExpanded
        {
            get
            {
                if (_itemExpanded == null)
                {
                    _itemExpanded = new RelayCommand<Tree<Product>>(o => this.OnItemExpanded(o));
                }
                return _itemExpanded;
            }
        }

展开事件：

private void OnItemExpanded(Tree<Product> item)
        {
            var lstChildren = 获取数据;
            if (lstChildren == null || lstChildren.Count <= 0)
            {
                item.Children.Clear();
                return;
            }


            item.Children.Clear();
            foreach (Product i in lstChildren)
            {
                item.Children.Add(new Tree<Product>(i, BuildLoadingChild()));
            }
        }