在WPF应用程序开发中，DataGrid控件是展示和操作数据的重要组件。本文将介绍如何通过MVVM模式实现DataGrid中的行拖拽合并功能。MVVM模式是一种设计模式，它将用户界面（View）与业务逻辑（ViewModel）分离，使得应用程序更加模块化和易于维护。
本文将展示如何在DataGrid控件中实现行的拖拽合并功能。在MVVM模式下，所有的拖拽合并逻辑都将被封装在ViewModel中，并通过附加依赖属性（Attached Dependency Properties）与视图（View）中的委托命令（DelegateCommand）绑定。
要实现DataGrid的拖拽功能，首先需要在XAML中设置一些属性绑定：
<WpfToolkit:DataGrid x:Name="listView" RowHeight="30" ItemsSource="{Binding Path=Items}" AutoGenerateColumns="False" SelectionMode="Single" AllowDrop="True" MouseMove="OnMainGridMouseMove" localControls:MouseMoveInGridSupport.MouseMoveCommand="{Binding MouseMoveCommand}" localControls:MouseDropInGridSupport.MouseDropCommand="{Binding MouseDropCommand}">
其中，AllowDrop属性被设置为True，以启用DataGrid的拖拽放置功能。
在代码后台（code-behind），需要处理MouseMove事件，以便在鼠标移动时检测到拖拽操作。
private void OnMainGridMouseMove(object sender, MouseEventArgs e)
{
if (e.LeftButton != MouseButtonState.Pressed)
{
e.Handled = true;
return;
}
var row = FindVisualParent(e.OriginalSource as FrameworkElement);
if ((row != null) && row.IsSelected)
{
var selectedItem = row.Item;
var finalDropEffect = DragDrop.DoDragDrop(row, selectedItem, DragDropEffects.Move);
if (finalDropEffect == DragDropEffects.Move)
{
e.Handled = false;
}
}
}
此代码段展示了如何检测鼠标移动事件，并在检测到拖拽操作时，执行拖拽放置操作。
在DataGrid的XAML中，使用了两个附加依赖属性：MouseMoveInGridSupport和MouseDropInGridSupport。
public class MouseMoveInGridSupport : ItemSupportBase
{
public static ICommand GetMouseMoveCommand(DependencyObject obj)
{
return (ICommand)obj.GetValue(MouseMoveCommandProperty);
}
public static void SetMouseMoveCommand(DependencyObject obj, ICommand value)
{
obj.SetValue(MouseMoveCommandProperty, value);
}
public static readonly DependencyProperty MouseMoveCommandProperty =
DependencyProperty.RegisterAttached(
"MouseMoveCommand",
typeof(ICommand),
typeof(MouseMoveInGridSupport),
new UIPropertyMetadata(null, new PropertyChangedCallback(OnCommandChanged)));
private static void OnCommandChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
{
if (e.OldValue != null)
((ItemsControl)sender).MouseMove -= new MouseEventHandler(OnMouseMoveClick);
if (e.NewValue != null)
((ItemsControl)sender).MouseMove += new MouseEventHandler(OnMouseMoveClick);
}
private static void OnMouseMoveClick(object sender, MouseEventArgs e)
{
DependencyObject source = (DependencyObject)e.OriginalSource;
var row = TryFindParent(source);
var item = row.Item;
if (item == null)
return;
var command = GetMouseMoveCommand((DependencyObject)sender);
if (command != null)
{
if (command.CanExecute(item))
command.Execute(item);
}
}
}
MouseMoveInGridSupport类用于检测DataGrid中的MouseMove事件，找到相关的DataGridRow，并将DataItem传递给ViewModel中的DelegateCommand。
在ViewModel中，定义了拖拽合并的逻辑。
public class MainViewModel : ViewModelBase
{
private Item dragItem;
private Item dropItem;
private DelegateCommand exitCommand;
public DelegateCommand- MouseMoveCommand { get; private set; }
public DelegateCommand
- MouseDropCommand { get; private set; }
public MainViewModel()
{
_items = DataAccess.DataAccess.LoadItems();
MouseMoveCommand = new DelegateCommand
- (MouseMove, CanMouseMove);
MouseDropCommand = new DelegateCommand
- (MouseDrop, CanMouseDrop);
}
private void MouseMove(Item item)
{
IList
- items = new List
- (_items);
dragItem = item;
if (dropItem != null && dragItem != null)
{
Item newItem = new Item();
newItem.Name = "Merge row: " + dragItem.Name + "" + dropItem.Name;
newItem.Data = (dropItem.Data + dragItem.Data) + 100;
newItem.Id = (dropItem.Id + dragItem.Id) + 100;
items.Remove(dragItem);
items.Remove(dropItem);
items.Add(newItem);
Items = items;
}
}
private bool CanMouseMove(Item item)
{
return true;
}
private void MouseDrop(Item item)
{
dropItem = item;
}
private bool CanMouseDrop(Item item)
{
return true;
}
}
在ViewModel中，定义了MouseMoveCommand和MouseDropCommand两个委托命令。MouseMoveCommand用于获取移动的项，然后与MouseDropCommand获取的放置项合并。