WPF实现Drag/Drop操作

Posted 2022-01-02 lonelyxmas

原文: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>