Control.AllowDrop 属性
获取或设置一个值，该值指示控件是否可以接受用户拖放到它上面的数据。
**命名空间:**System.Windows.Forms
**程序集:**System.Windows.Forms（在 system.windows.forms.dll 中）
语法
声明
Public Overridable Property AllowDrop As Boolean
用法
Dim instance As Control
Dim value As Boolean
value = instance.AllowDrop
instance.AllowDrop = value
public virtual bool AllowDrop { get; set; }
public:
virtual property bool AllowDrop {
bool get ();
void set (bool value);
}
/** @property */
public boolean get_AllowDrop ()
/** @property */
public void set_AllowDrop (boolean value)
public function get AllowDrop () : boolean
public function set AllowDrop (value : boolean)
属性值
如果控件允许拖放操作，则为 true；否则为 false。默认为 false。
备注
给继承者的说明 在派生类中重写 AllowDrop 属性时，请使用基类的 AllowDrop 属性来扩展基实现。否则，您必须提供所有实现。不需要同时重写 AllowDrop 属性的 get 和 set 访问器；如果需要，可以只重写其中一个访问器。
示例
下面的代码示例使用户能够将图像或图像文件拖到窗体上，并使它在放置点显示。每次绘制窗体时，都重写 OnPaint 方法以重新绘制图像；否则图像将保持到下一次重新绘制。DragEnter 事件处理方法决定拖到窗体中的数据的类型，并提供适当的反馈。如果 Image 可以从该数据中创建，则 DragDrop 事件处理方法就会在该窗体上显示此图像。因为 DragEventArgs.X 和 DragEventArgs.Y 值为屏幕坐标，所以示例使用 PointToClient 方法将它们转换成工作区坐标。
Private picture As Image
Private pictureLocation As Point
Public Sub New()
' Enable drag-and-drop operations.
Me.AllowDrop = True
End Sub
Protected Overrides Sub OnPaint(ByVal e As PaintEventArgs)
MyBase.OnPaint(e)
' If there is an image and it has a location,
' paint it when the Form is repainted.
If Not (Me.picture Is Nothing) And _
Not (Me.pictureLocation.Equals(Point.Empty)) Then
e.Graphics.DrawImage(Me.picture, Me.pictureLocation)
End If
End Sub
Private Sub Form1_DragDrop(ByVal sender As Object, _
ByVal e As DragEventArgs) Handles MyBase.DragDrop
' Handle FileDrop data.
If e.Data.GetDataPresent(DataFormats.FileDrop) Then
' Assign the file names to a string array, in
' case the user has selected multiple files.
Dim files As String() = CType(e.Data.GetData(DataFormats.FileDrop), String())
Try
' Assign the first image to the 'picture' variable.
Me.picture = Image.FromFile(files(0))
' Set the picture location equal to the drop point.
Me.pictureLocation = Me.PointToClient(New Point(e.X, e.Y))
Catch ex As Exception
MessageBox.Show(ex.Message)
Return
End Try
End If
' Handle Bitmap data.
If e.Data.GetDataPresent(DataFormats.Bitmap) Then
Try
' Create an Image and assign it to the picture variable.
Me.picture = CType(e.Data.GetData(DataFormats.Bitmap), Image)
' Set the picture location equal to the drop point.
Me.pictureLocation = Me.PointToClient(New Point(e.X, e.Y))
Catch ex As Exception
MessageBox.Show(ex.Message)
Return
End Try
End If
' Force the form to be redrawn with the image.
Me.Invalidate()
End Sub
Private Sub Form1_DragEnter(ByVal sender As Object, _
ByVal e As DragEventArgs) Handles MyBase.DragEnter
' If the data is a file or a bitmap, display the copy cursor.
If e.Data.GetDataPresent(DataFormats.Bitmap) _
Or e.Data.GetDataPresent(DataFormats.FileDrop) Then
e.Effect = DragDropEffects.Copy
Else
e.Effect = DragDropEffects.None
End If
End Sub
private Image picture;
private Point pictureLocation;
public Form1()
{
// Enable drag-and-drop operations and
// add handlers for DragEnter and DragDrop.
this.AllowDrop = true;
this.DragDrop += new DragEventHandler(this.Form1_DragDrop);
this.DragEnter += new DragEventHandler(this.Form1_DragEnter);
}
protected override void OnPaint(PaintEventArgs e)
{
// If there is an image and it has a location,
// paint it when the Form is repainted.
base.OnPaint(e);
if(this.picture != null && this.pictureLocation != Point.Empty)
{
e.Graphics.DrawImage(this.picture, this.pictureLocation);
}
}
private void Form1_DragDrop(object sender, DragEventArgs e)
{
// Handle FileDrop data.
if(e.Data.GetDataPresent(DataFormats.FileDrop) )
{
// Assign the file names to a string array, in
// case the user has selected multiple files.
string[] files = (string[])e.Data.GetData(DataFormats.FileDrop);
try
{
// Assign the first image to the picture variable.
this.picture = Image.FromFile(files[0]);
// Set the picture location equal to the drop point.
this.pictureLocation = this.PointToClient(new Point(e.X, e.Y) );
}
catch(Exception ex)
{
MessageBox.Show(ex.Message);
return;
}
}
// Handle Bitmap data.
if(e.Data.GetDataPresent(DataFormats.Bitmap) )
{
try
{
// Create an Image and assign it to the picture variable.
this.picture = (Image)e.Data.GetData(DataFormats.Bitmap);
// Set the picture location equal to the drop point.
this.pictureLocation = this.PointToClient(new Point(e.X, e.Y) );
}
catch(Exception ex)
{
MessageBox.Show(ex.Message);
return;
}
}
// Force the form to be redrawn with the image.
this.Invalidate();
}
private void Form1_DragEnter(object sender, DragEventArgs e)
{
// If the data is a file or a bitmap, display the copy cursor.
if (e.Data.GetDataPresent(DataFormats.Bitmap) ||
e.Data.GetDataPresent(DataFormats.FileDrop) )
{
e.Effect = DragDropEffects.Copy;
}
else
{
e.Effect = DragDropEffects.None;
}
}
private:
Image^ picture;
Point pictureLocation;
public:
Form1()
{
// Enable drag-and-drop operations and
// add handlers for DragEnter and DragDrop.
this->AllowDrop = true;
this->DragDrop += gcnew DragEventHandler( this, &Form1::Form1_DragDrop );
this->DragEnter += gcnew DragEventHandler( this, &Form1::Form1_DragEnter );
}
protected:
virtual void OnPaint( PaintEventArgs^ e ) override
{
// If there is an image and it has a location,
// paint it when the Form is repainted.
Form::OnPaint( e );
if ( this->picture != nullptr && this->pictureLocation != Point::Empty )
{
e->Graphics->DrawImage( this->picture, this->pictureLocation );
}
}
private:
void Form1_DragDrop( Object^ /*sender*/, DragEventArgs^ e )
{
// Handle FileDrop data.
if ( e->Data->GetDataPresent( DataFormats::FileDrop ) )
{
// Assign the file names to a String* array, in
// case the user has selected multiple files.
array<String^>^files = (array<String^>^)e->Data->GetData( DataFormats::FileDrop );
try
{
// Assign the first image to the picture variable.
this->picture = Image::FromFile( files[ 0 ] );
// Set the picture location equal to the drop point.
this->pictureLocation = this->PointToClient( Point(e->X,e->Y) );
}
catch ( Exception^ ex )
{
MessageBox::Show( ex->Message );
return;
}
}
// Handle Bitmap data.
if ( e->Data->GetDataPresent( DataFormats::Bitmap ) )
{
try
{
// Create an Image and assign it to the picture variable.
this->picture = dynamic_cast<Image^>(e->Data->GetData( DataFormats::Bitmap ));
// Set the picture location equal to the drop point.
this->pictureLocation = this->PointToClient( Point(e->X,e->Y) );
}
catch ( Exception^ ex )
{
MessageBox::Show( ex->Message );
return;
}
}
// Force the form to be redrawn with the image.
this->Invalidate();
}
void Form1_DragEnter( Object^ /*sender*/, DragEventArgs^ e )
{
// If the data is a file or a bitmap, display the copy cursor.
if ( e->Data->GetDataPresent( DataFormats::Bitmap ) || e->Data->GetDataPresent( DataFormats::FileDrop ) )
{
e->Effect = DragDropEffects::Copy;
}
else
{
e->Effect = DragDropEffects::None;
}
}
private Image picture;
private Point pictureLocation;
public Form1()
{
// Enable drag-and-drop operations and
// add handlers for DragEnter and DragDrop.
this.set_AllowDrop(true);
this.add_DragDrop(new DragEventHandler(this.Form1_DragDrop));
this.add_DragEnter(new DragEventHandler(this.Form1_DragEnter));
} //Form1
protected void OnPaint(PaintEventArgs e)
{
// If there is an image and it has a location,
// paint it when the Form is repainted.
super.OnPaint(e);
if (this.picture != null && !this.pictureLocation.Equals(Point.Empty)) {
e.get_Graphics().DrawImage(this.picture, this.pictureLocation);
}
} //OnPaint
private void Form1_DragDrop(Object sender, DragEventArgs e)
{
// Handle FileDrop data.
if (e.get_Data().GetDataPresent(DataFormats.FileDrop)) {
// Assign the file names to a string array, in
// case the user has selected multiple files.
String files[] = (String[])(e.get_Data().GetData(
DataFormats.FileDrop));
try {
// Assign the first image to the picture variable.
this.picture = Image.FromFile(files.toString());
// Set the picture location equal to the drop point.
this.pictureLocation = this.PointToClient(new Point(e.get_X(),
e.get_Y()));
}
catch (System.Exception ex) {
MessageBox.Show(ex.get_Message());
return;
}
}
// Handle Bitmap data.
if (e.get_Data().GetDataPresent(DataFormats.Bitmap)) {
try {
// Create an Image and assign it to the picture variable.
this.picture = (Image)e.get_Data().GetData(DataFormats.Bitmap);
// Set the picture location equal to the drop point.
this.pictureLocation = this.PointToClient(new Point(e.get_X(),
e.get_Y()));
}
catch (System.Exception ex) {
MessageBox.Show(ex.get_Message());
return;
}
}
// Force the form to be redrawn with the image.
this.Invalidate();
} //Form1_DragDrop
private void Form1_DragEnter(Object sender, DragEventArgs e)
{
// If the data is a file or a bitmap, display the copy cursor.
if (e.get_Data().GetDataPresent(DataFormats.Bitmap) || e.get_Data().
GetDataPresent(DataFormats.FileDrop)) {
e.set_Effect(DragDropEffects.Copy);
}
else {
e.set_Effect(DragDropEffects.None);
}
} //Form1_DragEnter
.NET Framework 安全性
- UIPermission 若要进行无限制的剪贴板访问，将该属性设置为 true。关联的枚举：System.Security.Permissions.UIPermissionClipboard 的 AllClipboard 值
平台
Windows 98、Windows 2000 SP4、Windows CE、Windows Millennium Edition、Windows Mobile for Pocket PC、Windows Mobile for Smartphone、Windows Server 2003、Windows XP Media Center Edition、Windows XP Professional x64 Edition、Windows XP SP2、Windows XP Starter Edition
.NET Framework 并不是对每个平台的所有版本都提供支持。有关受支持版本的列表，请参见系统要求。
版本信息
.NET Framework
受以下版本支持：2.0、1.1、1.0
请参见
参考
Control 类
Control 成员
System.Windows.Forms 命名空间
DragEventArgs
DragOver
DragDrop
DragEnter
DragLeave
DoDragDrop