WPF实现Drag/Drop操作

有时候我们方便用户操作，总会把一下Copy/Paste 或者 input操作转换为Drag/Drop, WPF 跟之前WinForm 一样提供了一些实现方式方便开发人员进行开发。

要允许控件Drop操作，首先必须设置控件属性AllowDrop，这样控件才能产生DragOver/DragEnter/Drop等相关事件，从而开发人员可以做一些逻辑判断，设置DragEventArgs 的属性Effects 决定Drag的内容是否允许Drop. 下面是一个简单的例子：

创建两个ListBox, 一个里面有内容（名字为：EmployeeSource），另外一个（名字：SelectedEmployees）没有内容，允许用户从EmployeeSource 拖拽内容到SelectedEmployees。

1. 在Xaml中创建这两个ListBox, 并进行相关数据绑定

        <ListBox x:Name="SelectedEmployees" HorizontalAlignment="Left" Height="100" Margin="35,30,0,0"                  ItemsSource="{Binding SelectedEmployeeData}" DisplayMemberPath="Description"                  VerticalAlignment="Top" Width="275" AllowDrop="True"                  Drop="SelectedEmployees_Drop" DragOver="SelectedEmployees_DragOver" DragLeave="SelectedEmployees_DragLeave"                  MouseMove="SelectedEmployees_MouseMove"/><ListBox x:Name="EmployeeSource" DataContext="{Binding Source={StaticResource EmployeeList}}"                  SelectionMode="Single" HorizontalAlignment="Left" Height="100" Margin="35,255,0,0" VerticalAlignment="Top" Width="280"                  ItemsSource="{Binding Employees}" DisplayMemberPath="Description" MouseMove="EmployeeSource_MouseMove"/>

2. 在cs文件中实现相关事件函数

        bool bMouseDown = true;        private void EmployeeSource_MouseMove(object sender, System.Windows.Input.MouseEventArgs e)        {        // TODO: Add event handler implementation here.            bMouseDown = e.LeftButton == MouseButtonState.Pressed;            if (EmployeeSource.SelectedItems.Count == 0 || !bMouseDown)                return;            ICollection<EmployeesItem> selected = new List<EmployeesItem>();            foreach(var item in EmployeeSource.SelectedItems)            {                var employee = item as EmployeesItem;                if (employee == null)                    return;                selected.Add(employee);            }            DragDrop.DoDragDrop(EmployeeSource, selected, DragDropEffects.Copy);        }        private void SelectedEmployees_Drop(object sender, System.Windows.DragEventArgs e)        {        // TODO: Add event handler implementation here.            var ems = e.Data.GetData(typeof(List<EmployeesItem>)) as List<EmployeesItem>;            if (ems == null)                return;                        foreach(var em in ems)            {                SelectedEmployeeData.Add(em);            }        }        private void SelectedEmployees_DragOver(object sender, System.Windows.DragEventArgs e)        {        // TODO: Add event handler implementation here.            var ems = e.Data.GetData(typeof(List<EmployeesItem>)) as List<EmployeesItem>;            if (ems == null)            {                e.Effects = DragDropEffects.None;                return;            }            DragElement = ems[0];            e.Effects = DragDropEffects.Copy;        }

3. 增加DataContext(ViewModel), 设置绑定的属性

public class EmployeeList : INotifyPropertyChanged{public event PropertyChangedEventHandler PropertyChanged;protected virtual void OnPropertyChanged(string propertyName){if (this.PropertyChanged != null){this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));}}public EmployeeList(){try{Uri resourceUri = new Uri("/WPFStudy;component/SampleData/EmployeeList/EmployeeList.xaml", UriKind.RelativeOrAbsolute);System.Windows.Application.LoadComponent(this, resourceUri);}catch{}}private Employees _Employees = new Employees();public Employees Employees{get{return this._Employees;}}}public class EmployeesItem : INotifyPropertyChanged{public event PropertyChangedEventHandler PropertyChanged;protected virtual void OnPropertyChanged(string propertyName){if (this.PropertyChanged != null){this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));}}

        public override bool Equals(object obj)

        {

            var tmp = obj as EmployeesItem;

            if (tmp == null) return false;

            return tmp.Description.Equals(Description);

        }

private string _Description = string.Empty;public string Description{get{return this._Description;}set{if (this._Description != value){this._Description = value;this.OnPropertyChanged("Description");}}}}public class Employees : System.Collections.ObjectModel.ObservableCollection<EmployeesItem>{ }