asp.net DoDragDrop asp.net DoDragDrop 方法的使用

时间:2021-03-18 人气:0

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在类库中的定义为:

 
[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 bands 
// that may be at the top or left side of the screen when 
// determining when to cancel the drag drop operation. 
screenOffset = SystemInformation.WorkingArea.Location; 
// Proceed with the drag-and-drop, passing in the list item. 
DragDropEffects dropEffect = ListDragSource.DoDragDrop(ListDragSource.Items[indexOfItemUnderMouseToDrag], DragDropEffects.All | DragDropEffects.Link); 
// If the drag operation was a move then remove the item. 
if (dropEffect == DragDropEffects.Move) { 
ListDragSource.Items.RemoveAt(indexOfItemUnderMouseToDrag); 
// Selects the previous item in the list as long as the list has an item. 
if (indexOfItemUnderMouseToDrag > 0) 
ListDragSource.SelectedIndex = indexOfItemUnderMouseToDrag -1; 
else if (ListDragSource.Items.Count > 0) 
// Selects the first item. 
ListDragSource.SelectedIndex =0; 
} 
// Dispose of the cursors since they are no longer needed. 
if (MyNormalCursor != null) 
MyNormalCursor.Dispose(); 
if (MyNoDropCursor != null) 
MyNoDropCursor.Dispose(); 
} 
} 
} 
} 
private void ListDragSource_GiveFeedback(object sender, System.Windows.Forms.GiveFeedbackEventArgs e) 
{ 
// Use custom cursors if the check box is checked. 
if (UseCustomCursorsCheck.Checked) { 
// Sets the custom cursor based upon the effect. 
e.UseDefaultCursors = false; 
if ((e.Effect & DragDropEffects.Move) == DragDropEffects.Move) 
Cursor.Current = MyNormalCursor; 
else 
Cursor.Current = MyNoDropCursor; 
} 
} 
private void ListDragTarget_DragOver(object sender, System.Windows.Forms.DragEventArgs e) 
{ 
// Determine whether string data exists in the drop data. If not, then 
// the drop effect reflects that the drop cannot occur. 
if (!e.Data.GetDataPresent(typeof(System.String))) { 
e.Effect = DragDropEffects.None; 
DropLocationLabel.Text = "None - no string data."; 
return; 
} 
// Set the effect based upon the KeyState. 
if ((e.KeyState & (8+32)) == (8+32) && 
(e.AllowedEffect & DragDropEffects.Link) == DragDropEffects.Link) { 
// KeyState 8 + 32 = CTL + ALT 
// Link drag-and-drop effect. 
e.Effect = DragDropEffects.Link; 
} else if ((e.KeyState & 32) == 32 && 
(e.AllowedEffect & DragDropEffects.Link) == DragDropEffects.Link) { 
// ALT KeyState for link. 
e.Effect = DragDropEffects.Link; 
} else if ((e.KeyState & 4) == 4 && 
(e.AllowedEffect & DragDropEffects.Move) == DragDropEffects.Move) { 
// SHIFT KeyState for move. 
e.Effect = DragDropEffects.Move; 
} else if ((e.KeyState & 8) == 8 && 
(e.AllowedEffect & DragDropEffects.Copy) == DragDropEffects.Copy) { 
// CTL KeyState for copy. 
e.Effect = DragDropEffects.Copy; 
} else if ((e.AllowedEffect & DragDropEffects.Move) == DragDropEffects.Move) { 
// By default, the drop action should be move, if allowed. 
e.Effect = DragDropEffects.Move; 
} else 
e.Effect = DragDropEffects.None; 
// Get the index of the item the mouse is below. 
// The mouse locations are relative to the screen, so they must be 
// converted to client coordinates. 
indexOfItemUnderMouseToDrop = 
ListDragTarget.IndexFromPoint(ListDragTarget.PointToClient(new Point(e.X, e.Y))); 
// Updates the label text. 
if (indexOfItemUnderMouseToDrop != ListBox.NoMatches){ 
DropLocationLabel.Text = "Drops before item #" + (indexOfItemUnderMouseToDrop + 1); 
} else 
DropLocationLabel.Text = "Drops at the end."; 
} 
private void ListDragTarget_DragDrop(object sender, System.Windows.Forms.DragEventArgs e) 
{ 
// Ensure that the list item index is contained in the data. 
if (e.Data.GetDataPresent(typeof(System.String))) { 
Object item = (object)e.Data.GetData(typeof(System.String)); 
// Perform drag-and-drop, depending upon the effect. 
if (e.Effect == DragDropEffects.Copy || 
e.Effect == DragDropEffects.Move) { 
// Insert the item. 
if (indexOfItemUnderMouseToDrop != ListBox.NoMatches) 
ListDragTarget.Items.Insert(indexOfItemUnderMouseToDrop, item); 
else 
ListDragTarget.Items.Add(item); 
} 
} 
// Reset the label text. 
DropLocationLabel.Text = "None"; 
} 
private void ListDragSource_QueryContinueDrag(object sender, System.Windows.Forms.QueryContinueDragEventArgs e) { 
// Cancel the drag if the mouse moves off the form. 
ListBox lb = sender as ListBox; 
if (lb != null) { 
Form f = lb.FindForm(); 
// Cancel the drag if the mouse moves off the form. The screenOffset 
// takes into account any desktop bands that may be at the top or left 
// side of the screen. 
if (((Control.MousePosition.X - screenOffset.X) < f.DesktopBounds.Left) || 
((Control.MousePosition.X - screenOffset.X) > f.DesktopBounds.Right) || 
((Control.MousePosition.Y - screenOffset.Y) < f.DesktopBounds.Top) || 
((Control.MousePosition.Y - screenOffset.Y) > f.DesktopBounds.Bottom)) { 
e.Action = DragAction.Cancel; 
} 
} 
} 
private void ListDragTarget_DragEnter(object sender, System.Windows.Forms.DragEventArgs e) { 
// Reset the label text. 
DropLocationLabel.Text = "None"; 
} 
private void ListDragTarget_DragLeave(object sender, System.EventArgs e) { 
// Reset the label text. 
DropLocationLabel.Text = "None"; 
} 
} 
} 

对用这种拖放操作和微软的服务，容器模式的关系，留在以后再学习。

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