MVVM模式下实现拖拽

在文章开始之前先看一看效果图

我们可以拖拽一个"游戏"给ListBox,并且ListBox也能接受拖拽过来的数据， 但是我们不能拖拽一个"游戏类型"给它。

所以当拖拽开始发生的时候我们必须添加一些限制条件，以防止接受不正确的数据。

Item实体

CS

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public class ItemModel : ViewModelBase {     public string ItemName { get; set; } }

组实体

CS

public class GroupModel : ViewModelBase
    {
        /// <summary>
        /// 组名
        /// </summary>
        public string GroupName { get; set; }
 
        private int groupCount;
        /// <summary>
        /// 组数量
        /// </summary>
        public int GroupCount
        {
            get { return groupCount; }
            set { groupCount = value; base.RaisePropertyChanged("GroupCount"); }
        }
 
        /// <summary>
        /// 子类集合
        /// </summary>
        public ObservableCollection<ItemModel> ItemModelList { get; set; }
    }

给"游戏"实体创建一个模板

XAML

<HierarchicalDataTemplate x:Key="template_Item">
       <TextBlock Text="{Binding ItemName}"/>
</HierarchicalDataTemplate>

给"游戏组"实体创建一个模板

XAML

<HierarchicalDataTemplate x:Key="template_Group" ItemsSource="{Binding ItemModelList}" ItemTemplate="{StaticResource template_Item}">
       <StackPanel Orientation="Horizontal">
              <TextBlock Text="{Binding GroupName}"/>
              <TextBlock Text="{Binding GroupCount}" Margin="5,0,0,0"/>
        </StackPanel>
</HierarchicalDataTemplate>

但是当我准备给TreeView赋值的时候 , 我想起来TreeView的SelectedItem属性不是依赖属性 , 它不支持Binding操作

所以只有自己写一个控件继承TreeView了。为它扩展一个MySelectedItem属性出来。并且重写SelectedItemChange事件

把TreeView的SelectedItem交给扩展的依赖属性MySelectedItem .这样在界面上就可以Binding选中项了

不过由于TreeView各个节点的数据实体可能类型不相同，所以扩展的属性只能定义为object类型

创建自定义树

CS

public class MyTreeView : TreeView
    {
        public MyTreeView()
        {
 
        }
 
        /// <summary>
        /// 自定义TreeView选中项,支持数据Binding
        /// </summary>
        public object MySelectItem
        {
            get { return GetValue(MySelectItemProperty); }
            set { SetValue(MySelectItemProperty, value); }
        }
 
        public static DependencyProperty MySelectItemProperty = DependencyProperty.Register("MySelectItem", typeof(object), typeof(MyTreeView));
 
        /// <summary>
        /// 当改变发生时,为自定义的SelectItem属性赋值
        /// </summary>
        /// <param name="e"></param>
        protected override void OnSelectedItemChanged(RoutedPropertyChangedEventArgs<object> e)
        {
            if (this.SelectedItem != null)
                this.MySelectItem = this.SelectedItem;
            base.OnSelectedItemChanged(e);
        }
    }

XAML

 <mc:MyTreeView x:Name="myTree" MouseMove="TreeView_MouseMove" TextBlock.FontSize="14" MySelectItem="{Binding SelectGame,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}" ItemsSource="{Binding GroupSourceList}" ItemTemplate="{StaticResource template_Group}">
</mc:MyTreeView>

CS

        private TreeViewItem ti = new TreeViewItem();
 
        private void TreeView_MouseMove(object sender, MouseEventArgs e)
        {
            if (e.LeftButton == MouseButtonState.Pressed)
            {
                if (myTree.SelectedItem == null)
                    return;
                DragDrop.DoDragDrop(ti, sender, DragDropEffects.Move);
            }
        }

DragDrop.DoDragDrop方法需要传入一个DependencyObject对象以设置其拖拽时的效果。

但由于TreeView做了数据绑定， 所以它的SelectItem取出来是一个数据实体。而不是一个DependencyObject对象了。

所以我用了一个比较SB的办法就是new一个TreeViewItem。然后设置拖拽移动的效果。

创建ListBox

           <ListBox ItemsSource="{Binding GameSourceList}" AllowDrop="true">
                <ListBox.ItemTemplate>
                    <DataTemplate>
                        <TextBlock Text="{Binding ItemName}"/>
                    </DataTemplate>
                </ListBox.ItemTemplate>
                <i:Interaction.Triggers>
                    <i:EventTrigger EventName="DragEnter">
                        <Command:EventToCommand Command="{Binding DragEnterCommand}" PassEventArgsToCommand="True"/>
                    </i:EventTrigger>
                    <i:EventTrigger EventName="DragOver">
                        <Command:EventToCommand Command="{Binding DragEnterCommand}" PassEventArgsToCommand="True"/>
                    </i:EventTrigger>
                    <i:EventTrigger EventName="Drop">
                        <Command:EventToCommand Command="{Binding DropCommand}" PassEventArgsToCommand="True"/>
                    </i:EventTrigger>
                </i:Interaction.Triggers>
            </ListBox>

ViewModel

public class MainViewModel : ViewModelBase
    {
        public MainViewModel()
        {
            Init();
        }
 
        #region Properties
        /// <summary>
        /// 数据源
        /// </summary>
        public ObservableCollection<GroupModel> GroupSourceList { get; set; }
 
        /// <summary>
        /// 数据源
        /// </summary>
        public ObservableCollection<ItemModel> GameSourceList { get; set; }
 
        private object selectGame;
        /// <summary>
        /// 当前选中项
        /// </summary>
        public object SelectGame
        {
            get { return selectGame; }
            set
            {
                selectGame = value;
                base.RaisePropertyChanged("SelectGame");
            }
        }
        #endregion
 
        #region Methods
        private void Init()
        {
            GameSourceList = new ObservableCollection<ItemModel>();
            GroupSourceList = new ObservableCollection<GroupModel>();
            GroupModel gp1 = new GroupModel();
            #region 模拟数据
            gp1.GroupName = "竞技游戏";
            gp1.ItemModelList = new ObservableCollection<ItemModel>();
            gp1.ItemModelList.Add(new ItemModel() { ItemName = "CS GO" });
            gp1.ItemModelList.Add(new ItemModel() { ItemName = "星际争霸2" });
            gp1.ItemModelList.Add(new ItemModel() { ItemName = "FIFA 14" });
            gp1.GroupCount = gp1.ItemModelList.Count;
            GroupModel gp2 = new GroupModel();
            gp2.GroupName = "网络游戏";
            gp2.ItemModelList = new ObservableCollection<ItemModel>();
            gp2.ItemModelList.Add(new ItemModel() { ItemName = "CS OnLine" });
            gp2.ItemModelList.Add(new ItemModel() { ItemName = "街头篮球" });
            gp2.ItemModelList.Add(new ItemModel() { ItemName = "完美世界" });
            gp2.GroupCount = gp2.ItemModelList.Count;
            GroupModel gp3 = new GroupModel();
            gp3.GroupName = "休闲游戏";
            gp3.ItemModelList = new ObservableCollection<ItemModel>();
            gp3.ItemModelList.Add(new ItemModel() { ItemName = "德州扑克" });
            gp3.ItemModelList.Add(new ItemModel() { ItemName = "街头篮球" });
            gp3.ItemModelList.Add(new ItemModel() { ItemName = "完美世界" });
            GroupSourceList.Add(gp1);
            GroupSourceList.Add(gp2);
            GroupSourceList.Add(gp3);
            gp3.GroupCount = gp3.ItemModelList.Count;
            #endregion
            DragEnterCommand = new RelayCommand<DragEventArgs>(DragEnter);
            DropCommand = new RelayCommand<DragEventArgs>(Drop);
        }
 
        private void DragEnter(DragEventArgs args)
        {
            if (SelectGame.GetType() == typeof(ItemModel)) //如果拖拽的对象是"游戏"则接受之
            {
                args.Effects = DragDropEffects.Move;
                System.Console.WriteLine("accept");
            }
            else
            {
                args.Effects = DragDropEffects.None;       //否则拒绝接受拖拽
                System.Console.WriteLine("no accept");
            }
            args.Handled = true;
        }
 
        private void Drop(DragEventArgs args)
        {
            GameSourceList.Add(SelectGame as ItemModel);   //将接受到的"游戏"写入ListBox
        }
        #endregion
 
        #region Commands
 
        public ICommand DragEnterCommand { get; set; }
 
        public ICommand DropCommand { get; set; }
        #endregion
    }

到这里一个简单的拖拽就完成了。

原地址：http://www.cnblogs.com/ShenNan/p/4275494.html