机遇屋-WPF拖拽ListBox中的Item

WPF拖拽ListBox中的Item

作者：ych

### WPF列表拖拽

#### 需求一

两个ListBox，拖拽其中一个ListBox的Item，放置到另一个ListBox中

参考 http://www.c-sharpcorner.com/uploadfile/dpatra/drag-and-drop-item-in-listbox-in-wpf/ 右边ListBox2本来是空的，从左边ListBox1中拖拽了一个Item过去。

#### 需求二

单个ListBox，拖拽Item，释放后Item插入到鼠标所在位置，使ListBox的Items排序发生改变

尝试使用ObservableCollection创建一个
```
    ObservableCollection<Emp> _empList = new ObservableCollection<Emp>();

public Window1()
    {
        InitializeComponent();

_empList .Add(new Emp("1", 22));
        _empList .Add(new Emp("2", 18));
        _empList .Add(new Emp("3", 29));
        _empList .Add(new Emp("4", 9));
        _empList .Add(new Emp("5", 29));
        _empList .Add(new Emp("6", 9));
        listbox1.DisplayMemberPath = "Name";
        listbox1.ItemsSource = _empList;

Style itemContainerStyle = new Style(typeof(ListBoxItem));
        itemContainerStyle.Setters.Add(new Setter(ListBoxItem.AllowDropProperty, true));
        itemContainerStyle.Setters.Add(new EventSetter(ListBoxItem.PreviewMouseLeftButtonDownEvent, new MouseButtonEventHandler(s_PreviewMouseLeftButtonDown)));
        itemContainerStyle.Setters.Add(new EventSetter(ListBoxItem.DropEvent, new DragEventHandler(listbox1_Drop)));
        listbox1.ItemContainerStyle = itemContainerStyle;
    }
```

拖放过程：
```
    void s_PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
    {

if (sender is ListBoxItem)
        {
            ListBoxItem draggedItem = sender as ListBoxItem;
            DragDrop.DoDragDrop(draggedItem, draggedItem.DataContext, DragDropEffects.Move);
            draggedItem.IsSelected = true;
        }
    }

void listbox1_Drop(object sender, DragEventArgs e)
    {
        Emp droppedData = e.Data.GetData(typeof(Emp)) as Emp;
        Emp target = ((ListBoxItem)(sender)).DataContext as Emp;

int removedIdx = listbox1.Items.IndexOf(droppedData);
        int targetIdx = listbox1.Items.IndexOf(target);

if (removedIdx < targetIdx)
        {
            _empList.Insert(targetIdx + 1, droppedData);
            _empList.RemoveAt(removedIdx);
        }
        else
        {
            int remIdx = removedIdx+1;
            if (_empList.Count + 1 > remIdx)
            {
                _empList.Insert(targetIdx, droppedData);
                _empList.RemoveAt(remIdx);
            }
        }
    }
```

参考 https://stackoverflow.com/questions/3350187/wpf-c-rearrange-items-in-listbox-via-drag-and-drop 本来Item排序是从1到6的，拖拽5号Item以改变它在列表中的排序位置。

#### 案例参考
[wpf-drag-item-in-listbox](https://www.cnblogs.com/guxin/p/wpf-drag-item-in-listbox.html "wpf-drag-item-in-listbox")

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