MVVM模式下實現拖拽

原文:MVVM模式下實現拖拽

在文章開始之前先看一看效果圖

我們可以拖拽一個"游戲"給ListBox,并且ListBox也能接受拖拽過來的數據， 但是我們不能拖拽一個"游戲類型"給它。

所以當拖拽開始發生的時候我們必須添加一些限制條件，以防止接受不正確的數據。

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Item實體

CS

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

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組實體

CS

public class GroupModel : ViewModelBase{/// <summary>/// 組名/// </summary>public string GroupName { get; set; }private int groupCount;/// <summary>/// 組數量/// </summary>public int GroupCount{get { return groupCount; }set { groupCount = value; base.RaisePropertyChanged("GroupCount"); }}/// <summary>/// 子類集合/// </summary>public ObservableCollection<ItemModel> ItemModelList { get; set; }}

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給"游戲"實體創建一個模板

XAML

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

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給"游戲組"實體創建一個模板

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>

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但是當我準備給TreeView賦值的時候 , 我想起來TreeView的SelectedItem屬性不是依賴屬性 , 它不支持Binding操作

所以只有自己寫一個控件繼承TreeView了。為它擴展一個MySelectedItem屬性出來。并且重寫SelectedItemChange事件

把TreeView的SelectedItem交給擴展的依賴屬性MySelectedItem .這樣在界面上就可以Binding選中項了

不過由于TreeView各個節點的數據實體可能類型不相同，所以擴展的屬性只能定義為object類型

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創建自定義樹

CS

public class MyTreeView : TreeView{public MyTreeView(){}/// <summary>/// 自定義TreeView選中項,支持數據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>/// 當改變發生時,為自定義的SelectItem屬性賦值/// </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>

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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方法需要傳入一個DependencyObject對象以設置其拖拽時的效果。

但由于TreeView做了數據綁定， 所以它的SelectItem取出來是一個數據實體。而不是一個DependencyObject對象了。

所以我用了一個比較SB的辦法就是new一個TreeViewItem。然后設置拖拽移動的效果。

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創建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>/// 數據源/// </summary>public ObservableCollection<GroupModel> GroupSourceList { get; set; }/// <summary>/// 數據源/// </summary>public ObservableCollection<ItemModel> GameSourceList { get; set; }private object selectGame;/// <summary>/// 當前選中項/// </summary>public object SelectGame{get { return selectGame; }set{selectGame = value;base.RaisePropertyChanged("SelectGame");}}#endregion#region Methodsprivate void Init(){GameSourceList = new ObservableCollection<ItemModel>();GroupSourceList = new ObservableCollection<GroupModel>();GroupModel gp1 = new GroupModel();#region 模擬數據gp1.GroupName = "競技游戲";gp1.ItemModelList = new ObservableCollection<ItemModel>();gp1.ItemModelList.Add(new ItemModel() { ItemName = "CS GO" });gp1.ItemModelList.Add(new ItemModel() { ItemName = "星際爭霸2" });gp1.ItemModelList.Add(new ItemModel() { ItemName = "FIFA 14" });gp1.GroupCount = gp1.ItemModelList.Count;GroupModel gp2 = new GroupModel();gp2.GroupName = "網絡游戲";gp2.ItemModelList = new ObservableCollection<ItemModel>();gp2.ItemModelList.Add(new ItemModel() { ItemName = "CS OnLine" });gp2.ItemModelList.Add(new ItemModel() { ItemName = "街頭籃球" });gp2.ItemModelList.Add(new ItemModel() { ItemName = "完美世界" });gp2.GroupCount = gp2.ItemModelList.Count;GroupModel gp3 = new GroupModel();gp3.GroupName = "休閑游戲";gp3.ItemModelList = new ObservableCollection<ItemModel>();gp3.ItemModelList.Add(new ItemModel() { ItemName = "德州撲克" });gp3.ItemModelList.Add(new ItemModel() { ItemName = "街頭籃球" });gp3.ItemModelList.Add(new ItemModel() { ItemName = "完美世界" });GroupSourceList.Add(gp1);GroupSourceList.Add(gp2);GroupSourceList.Add(gp3);gp3.GroupCount = gp3.ItemModelList.Count;#endregionDragEnterCommand = new RelayCommand<DragEventArgs>(DragEnter);DropCommand = new RelayCommand<DragEventArgs>(Drop);}private void DragEnter(DragEventArgs args){if (SelectGame.GetType() == typeof(ItemModel)) //如果拖拽的對象是"游戲"則接受之
            {args.Effects = DragDropEffects.Move;System.Console.WriteLine("accept");}else{args.Effects = DragDropEffects.None;       //否則拒絕接受拖拽System.Console.WriteLine("no accept");}args.Handled = true;}private void Drop(DragEventArgs args){GameSourceList.Add(SelectGame as ItemModel);   //將接受到的"游戲"寫入ListBox
        }#endregion#region Commandspublic ICommand DragEnterCommand { get; set; }public ICommand DropCommand { get; set; }#endregion}

到這里一個簡單的拖拽就完成了。

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