ItemDragEventHandler 代理人

定義

命名空間:

System.Windows.Forms

組件:

System.Windows.Forms.dll

來源:

ItemDragEventHandler.cs

表示處理 ListView 或 TreeView 控制項的 ItemDrag 事件的方法。

C#

public delegate void ItemDragEventHandler(object? sender, ItemDragEventArgs e);

參數

sender

Object

事件的來源。

e

ItemDragEventArgs

包含事件資料的 ItemDragEventArgs。

範例

下列範例示範如何在控制項內 TreeView 啟用拖放作業。 在此範例中，任何節點都可以拖曳至另一個不是拖曳節點子代的節點。 拖曳的節點，包括其所有子代節點，都會成為目的地節點的子節點。 使用滑鼠左鍵時，拖曳的節點會移至目的地節點。 使用滑鼠右鍵時，拖曳的節點會複製到目的地節點。

C#

using System;
using System.Drawing;
using System.Windows.Forms;

public class Form1 : Form
{
    private TreeView treeView1;

    public Form1()
    {
        treeView1 = new TreeView();

        this.SuspendLayout();

        // Initialize treeView1.
        treeView1.AllowDrop = true;
        treeView1.Dock = DockStyle.Fill;

        // Add nodes to treeView1.
        TreeNode node;
        for (int x = 0; x < 3; ++x)
        {
            // Add a root node to treeView1.
            node = treeView1.Nodes.Add(String.Format("Node{0}", x*4));
            for (int y = 1; y < 4; ++y)
            {
                // Add a child node to the previously added node.
                node = node.Nodes.Add(String.Format("Node{0}", x*4 + y));
            }
        }

        // Add event handlers for the required drag events.
        treeView1.ItemDrag += new ItemDragEventHandler(treeView1_ItemDrag);
        treeView1.DragEnter += new DragEventHandler(treeView1_DragEnter);
        treeView1.DragOver += new DragEventHandler(treeView1_DragOver);
        treeView1.DragDrop += new DragEventHandler(treeView1_DragDrop);

        // Initialize the form.
        this.ClientSize = new Size(292, 273);
        this.Controls.Add(treeView1);

        this.ResumeLayout(false);
    }

    [STAThread]
    static void Main() 
    {
        Application.Run(new Form1());
    }

    private void treeView1_ItemDrag(object sender, ItemDragEventArgs e)
    {
        // Move the dragged node when the left mouse button is used.
        if (e.Button == MouseButtons.Left)
        {
            DoDragDrop(e.Item, DragDropEffects.Move);
        }

        // Copy the dragged node when the right mouse button is used.
        else if (e.Button == MouseButtons.Right)
        {
            DoDragDrop(e.Item, DragDropEffects.Copy);
        }
    }

    // Set the target drop effect to the effect 
    // specified in the ItemDrag event handler.
    private void treeView1_DragEnter(object sender, DragEventArgs e)
    {
        e.Effect = e.AllowedEffect;
    }

    // Select the node under the mouse pointer to indicate the 
    // expected drop location.
    private void treeView1_DragOver(object sender, DragEventArgs e)
    {
        // Retrieve the client coordinates of the mouse position.
        Point targetPoint = treeView1.PointToClient(new Point(e.X, e.Y));

        // Select the node at the mouse position.
        treeView1.SelectedNode = treeView1.GetNodeAt(targetPoint);
    }

    private void treeView1_DragDrop(object sender, DragEventArgs e)
    {
        // Retrieve the client coordinates of the drop location.
        Point targetPoint = treeView1.PointToClient(new Point(e.X, e.Y));

        // Retrieve the node at the drop location.
        TreeNode targetNode = treeView1.GetNodeAt(targetPoint);

        // Retrieve the node that was dragged.
        TreeNode draggedNode = (TreeNode)e.Data.GetData(typeof(TreeNode));

        // Confirm that the node at the drop location is not 
        // the dragged node or a descendant of the dragged node.
        if (!draggedNode.Equals(targetNode) && !ContainsNode(draggedNode, targetNode))
        {
            // If it is a move operation, remove the node from its current 
            // location and add it to the node at the drop location.
            if (e.Effect == DragDropEffects.Move)
            {
                draggedNode.Remove();
                targetNode.Nodes.Add(draggedNode);
            }

            // If it is a copy operation, clone the dragged node 
            // and add it to the node at the drop location.
            else if (e.Effect == DragDropEffects.Copy)
            {
                targetNode.Nodes.Add((TreeNode)draggedNode.Clone());
            }

            // Expand the node at the location 
            // to show the dropped node.
            targetNode.Expand();
        }
    }

    // Determine whether one node is a parent 
    // or ancestor of a second node.
    private bool ContainsNode(TreeNode node1, TreeNode node2)
    {
        // Check the parent node of the second node.
        if (node2.Parent == null) return false;
        if (node2.Parent.Equals(node1)) return true;

        // If the parent node is not null or equal to the first node, 
        // call the ContainsNode method recursively using the parent of 
        // the second node.
        return ContainsNode(node1, node2.Parent);
    }
}

備註

當您建立 ItemDragEventHandler 委派 (Delegate) 時，就可以識別即將處理此事件的方法。 若要使事件與您的事件處理常式產生關聯，請將委派的執行個體 (Instance) 加入至事件。 除非您移除委派，否則每當事件發生時就會呼叫事件處理常式。 如需事件處理常式委派的詳細資訊，請參閱 處理和引發事件。

擴充方法

適用於

另請參閱

• ItemDragEventArgs