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asp.net DoDragDrop 方法的使用

答案:在类库中的定义为:
复制代码 代码如下:

[UIPermissionAttribute(SecurityAction.Demand, Clipboard = UIPermissionClipboard.OwnClipboard)]
public DragDropEffects DoDragDrop(
Object data,
DragDropEffects allowedEffects
)

其中data参数为要拖放的数据,如果拖动操作需要于另一个进程的应用程序相互操作,data代表的数据应该是基本托管类(String,BitMap,或MetaFile),或者是实现 ISerializable 或IDataObject的对象。 allowedEffects参数表示拖放的效果,为一个枚举值(DragDropEffects).返回值也为DragDropEffects枚举值。
  当开始调用DoDragDrop方法拖动一个数据对象时,DoDragDrops在拖放过程中,检测当前光标位置下的控件是不是有效的放置目标。如果当前光标下的控件是有效的放置目标,则GiveFeedBack事件以指定的拖放效果引发。在检测当前位置光标是否为有效的拖放目标时,DoDragDrops方法同时跟踪光标位置,键盘状态和鼠标状态的更改。
   (1)如果用于移出了一个窗口,则引发DragLeave事件。
  (2)如果移入了另外一个控件,则引发该控件的DragEnter事件。
  (3)如果鼠标移动,但是停留在一个控件中,则引发DragOver事件。
如果检测到更改了键盘或者鼠标状态,则引发拖放源的QueryContinueDrag事件, 并根据事件的QueryContinueDragEventArgs的Action属性值确定继续拖动,放置数据或取消操作。
(1)如果Action属性指定为Continue,则将引发DragOver事件。
(2)如果Action属性指定为Drop,则将放置效果返回给源,以便应用程序对数据进行适当的操作;例如,如果是移动操作,则剪切数据。
(3)如果是DragAction的值为Cancel,则引发DragLeave事件
从csdn上摘抄一段示例代码:
  下面的代码示例演示在两个 ListBox 控件之间的拖放操作。当拖动动作启动时,该示例调用 DoDragDrop 方法。在 MouseDown 事件期间,如果从鼠标位置起鼠标移动的距离大于 SystemInformation..::.DragSize,则启动拖动动作。IndexFromPoint 方法用于确定在 MouseDown 事件期间要拖动的项的索引。
  该示例还演示如何对拖放操作使用自定义光标。该示例要求应用程序目录中存在两个光标文件:3dwarro.cur 和 3dwno.cur,分别用于自定义拖动光标和禁止停放光标。如果选中 UseCustomCursorsCheckCheckBox,则使用自定义光标。自定义光标在 GiveFeedback 事件处理程序中设置。
  键盘状态在右 ListBox 的 DragOver 事件处理程序中计算,以确定基于 Shift、Ctrl、Alt 或 Ctrl+Alt 键的状态将发生哪种拖动操作。放置动作在 ListBox 中发生的位置也在 DragOver 事件期间确定。如果要放置的数据不是 String,则 DragDropEffects 中将把 DragEventArgs.sEffect 设置为 None。最后,停放状态在 DropLocationLabelLabel 中显示。
  要放置的用于右 ListBox 的数据在 DragDrop 事件处理程序中确定,并且在 ListBox 中的适当位置添加该 String 值。如果拖动操作移动到窗体边框的外面,则 QueryContinueDrag 事件处理程序中将取消拖放操作
复制代码 代码如下:

using System;
using System.Drawing;
using System.Windows.Forms;
namespace Snip_DragNDrop
{
public class Form1 : System.Windows.Forms.Form
{
private System.Windows.Forms.ListBox ListDragSource;
private System.Windows.Forms.ListBox ListDragTarget;
private System.Windows.Forms.CheckBox UseCustomCursorsCheck;
private System.Windows.Forms.Label DropLocationLabel;
private int indexOfItemUnderMouseToDrag;
private int indexOfItemUnderMouseToDrop;
private Rectangle dragBoxFromMouseDown;
private Point screenOffset;
private Cursor MyNoDropCursor;
private Cursor MyNormalCursor;
/// The main entry point for the application.
[STAThread]
static void Main()
{
Application.Run(new Form1());
}
public Form1()
{
this.ListDragSource = new System.Windows.Forms.ListBox();
this.ListDragTarget = new System.Windows.Forms.ListBox();
this.UseCustomCursorsCheck = new System.Windows.Forms.CheckBox();
this.DropLocationLabel = new System.Windows.Forms.Label();
this.SuspendLayout();
// ListDragSource
this.ListDragSource.Items.AddRange(new object[] {"one", "two", "three", "four",
"five", "six", "seven", "eight",
"nine", "ten"});
this.ListDragSource.Location = new System.Drawing.Point(10, 17);
this.ListDragSource.Size = new System.Drawing.Size(120, 225);
this.ListDragSource.MouseDown += new System.Windows.Forms.MouseEventHandler(this.ListDragSource_MouseDown);
this.ListDragSource.QueryContinueDrag += new System.Windows.Forms.QueryContinueDragEventHandler(this.ListDragSource_QueryContinueDrag);
this.ListDragSource.MouseUp += new System.Windows.Forms.MouseEventHandler(this.ListDragSource_MouseUp);
this.ListDragSource.MouseMove += new System.Windows.Forms.MouseEventHandler(this.ListDragSource_MouseMove);
this.ListDragSource.GiveFeedback += new System.Windows.Forms.GiveFeedbackEventHandler(this.ListDragSource_GiveFeedback);
// ListDragTarget
this.ListDragTarget.AllowDrop = true;
this.ListDragTarget.Location = new System.Drawing.Point(154, 17);
this.ListDragTarget.Size = new System.Drawing.Size(120, 225);
this.ListDragTarget.DragOver += new System.Windows.Forms.DragEventHandler(this.ListDragTarget_DragOver);
this.ListDragTarget.DragDrop += new System.Windows.Forms.DragEventHandler(this.ListDragTarget_DragDrop);
this.ListDragTarget.DragEnter += new System.Windows.Forms.DragEventHandler(this.ListDragTarget_DragEnter);
this.ListDragTarget.DragLeave += new System.EventHandler(this.ListDragTarget_DragLeave);
// UseCustomCursorsCheck
this.UseCustomCursorsCheck.Location = new System.Drawing.Point(10, 243);
this.UseCustomCursorsCheck.Size = new System.Drawing.Size(137, 24);
this.UseCustomCursorsCheck.Text = "Use Custom Cursors";
// DropLocationLabel
this.DropLocationLabel.Location = new System.Drawing.Point(154, 245);
this.DropLocationLabel.Size = new System.Drawing.Size(137, 24);
this.DropLocationLabel.Text = "None";
// Form1
this.ClientSize = new System.Drawing.Size(292, 270);
this.Controls.AddRange(new System.Windows.Forms.Control[] {this.ListDragSource,
this.ListDragTarget, this.UseCustomCursorsCheck,
this.DropLocationLabel});
this.Text = "drag-and-drop Example";
this.ResumeLayout(false);
}
private void ListDragSource_MouseDown(object sender, System.Windows.Forms.MouseEventArgs e)
{
// Get the index of the item the mouse is below.
indexOfItemUnderMouseToDrag = ListDragSource.IndexFromPoint(e.X, e.Y);
if (indexOfItemUnderMouseToDrag != ListBox.NoMatches) {
// Remember the point where the mouse down occurred. The DragSize indicates
// the size that the mouse can move before a drag event should be started.
Size dragSize = SystemInformation.DragSize;
// Create a rectangle using the DragSize, with the mouse position being
// at the center of the rectangle.
dragBoxFromMouseDown = new Rectangle(new Point(e.X - (dragSize.Width /2),
e.Y - (dragSize.Height /2)), dragSize);
} else
// Reset the rectangle if the mouse is not over an item in the ListBox.
dragBoxFromMouseDown = Rectangle.Empty;
}
private void ListDragSource_MouseUp(object sender, System.Windows.Forms.MouseEventArgs e) {
// Reset the drag rectangle when the mouse button is raised.
dragBoxFromMouseDown = Rectangle.Empty;
}
private void ListDragSource_MouseMove(object sender, System.Windows.Forms.MouseEventArgs e)
{
if ((e.Button & MouseButtons.Left) == MouseButtons.Left) {
// If the mouse moves outside the rectangle, start the drag.
if (dragBoxFromMouseDown != Rectangle.Empty &&
!dragBoxFromMouseDown.Contains(e.X, e.Y)) {
// Create custom cursors for the drag-and-drop operation.
try {
MyNormalCursor = new Cursor("3dwarro.cur");
MyNoDropCursor = new Cursor("3dwno.cur");
} catch {
// An error occurred while attempting to load the cursors, so use
// standard cursors.
UseCustomCursorsCheck.Checked = false;
}finally {
// The screenOffset is used to account for any desktop b

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