ACC2000: How to Simulate Drag-And-Drop Capabilities

ID: Q233274

The information in this article applies to:

Microsoft Access 2000

Advanced: Requires expert coding, interoperability, and multiuser skills.

This article applies to a Microsoft Access database (.mdb) and a Microsoft Access project (.adp).

SUMMARY

Microsoft Access does not have a built-in DragDrop event for controls as does Visual Basic. This article describes how to create a DragDrop procedure that will run in response to a Microsoft Access control being dragged to another control.

This article provides two examples that demonstrate the use of the DragDrop procedure. The first example demonstrates how to drag the value in a control on one form to a control on a second form. The second example demonstrates how to move items from one list box to a second list box using a drag-and-drop procedure. If you perform a drag-and-drop procedure with the CTRL key held down, all items from one list will be moved to the second list.

MORE INFORMATION

The following four procedures, DragStart, DragStop, DropDetect, and DragDrop, are required to implement drag-and-drop capabilities between controls in Microsoft Access.

DragStart, DragStop

Enables a control to be dragged. DragStart and DragStop are called from the MouseDown and MouseUp events respectively for each control that you want to be capable of being dragged.

Syntax:


Sub DragStart(DragFrm As Form)

where DragFrm: is the form containing the control being dragged.


Sub DragStop()

Example:


Private Sub MyControl_MouseDown(Button As Integer, Shift As Integer, ...             
   DragStart Me
End Sub

Private Sub MyControl_MouseDown(Button As Integer, Shift As Integer, ...
   DragStop
End Sub

DropDetect

Enables a control to be a drop target. DropDetect should be called from the MouseMove event for each control that you want to be a drop target for a control being dragged.

Syntax:


Sub DropDetect(DropFrm As Form, DropCtrl As Control, _
   Button As Integer, Shift As Integer, _
   X As Single, Y As Single)

where:

DropFrm is the form containing the control being dropped on.

DropCtrl is the control being dropped on.

Button, Shift, X, Y are the parameters from the MouseMove event.

Example:


Private Sub MyControl_MouseMove(Button As Integer, Shift As ...
   DropDetect Me, Me![Employee ID], Button, Shift, X, Y
End Sub

NOTE: A control can be dragged and be a drop target by calling DragStart, DragStop, and DropDetect from the MouseDown, MouseUp, and MouseMove events respectively.

DragDrop

This procedure will be called in response to a drag-enabled control being dragged to a drop-enabled control. You will add your own code to this procedure to control what happens in response to a drop operation. For example you could copy the contents of the dragged control to the dropped control.

Syntax:


Sub DragDrop (DragFrm As Form, DragCtrl As Control, DropFrm As Form, _
   DropCtrl As Control, Button As Integer, Shift As Integer, _
   X As Single, Y As Single)

where:

DragFrm is the form containing the control being dragged.

DragCtrl is the control being dragged.

DropFrm is the form containing the control being dropped on.

DropCtrl is the control being dropped on.

Button is the state of the mouse buttons when the drop occurred.

Shift is the state of the SHIFT, CTRL, ALT keys when the drop occurred.

X, Y are the x and y coordinates of the mouse where the drop occurred.

NOTE: For more information on Button, Shift, X, Y arguments, search Help for the MouseMove event.

Example:

The following example will copy the contents of the drag control to the drop control, trapping and displaying any error that occurs:


Sub DragDrop (DragFrm As Form, DragCtrl As Control, ...
   On Error Resume Next
   DropCtrl = DragCtrl
   If Err Then MsgBox Error$
End Sub

EXAMPLE 1: Drag and Drop Between Controls on Two Forms

The following example demonstrates how to set the Salesperson combo box on the Northwind Orders form by dragging the EmployeeID field from the Employees form and dropping it into the Salesperson combo box.

Open the sample database Northwind.mdb.

Create a new module and type the following lines in the Declarations section:


Option Explicit

   Dim DragFrm As Form
   Dim DragCtrl As Control
   Dim DropTime

   Const MAX_DROP_TIME = .1

   Dim CurrentMode As Integer
   Const NO_MODE = 0
   Const DROP_MODE = 1
   Const DRAG_MODE = 2

Type the following three procedures:



Sub DragStart (SourceFrm As Form)
   ' NOTE: You should not use Screen.ActiveForm in place of
   ' SourceFrm because you may be dragging from a subform.
   Set DragFrm = SourceFrm
   Set DragCtrl = Screen.ActiveControl
   CurrentMode = DRAG_MODE
End Sub

Sub DragStop ()
   CurrentMode = DROP_MODE
   DropTime = Timer
End Sub

Sub DropDetect (DropFrm As Form, DropCtrl As Control, _
   Button As Integer, Shift As Integer, _
   X As Single, Y As Single)

   ' If a drop hasn't happened, then exit.
   If CurrentMode <> DROP_MODE Then Exit Sub
   CurrentMode = NO_MODE

   ' The timer interval is permitted between the MouseUp event and
   ' the MouseMove event. This ensures that the MouseMove event does
   ' not invoke the Drop procedure unless it is the MouseMove event
   ' that Microsoft Access automatically fires for the Drop control
   ' following the MouseUp event of a drag control. Subsequent
   ' MouseMove events will fail the timer test and be ignored.
   
   If Timer - DropTime > MAX_DROP_TIME Then Exit Sub

   ' Did we drag/drop onto ourselves?
   If (DragCtrl.Name <> DropCtrl.Name) Or _
         (DragFrm.hWnd <> DropFrm.hWnd) Then
      ' If not, then a successful drag/drop occurred.
      DragDrop DragFrm, DragCtrl, DropFrm, DropCtrl, Button, Shift, X, Y
   End If
End Sub

Type the following DragDrop procedure.

NOTE: This procedure does not have to appear in the same module as the procedures typed above. Because you will be customizing the contents of the DragDrop procedure to respond to a successful drag-and-drop operation, it may be better to place it in a separate module.


Sub DragDrop (DragFrm As Form, DragCtrl As Control, _
   DropFrm As Form, DropCtrl As Control, _
   Button As Integer, Shift As Integer, _
   X As Single, Y As Single)

   On Error Resume Next
   DropCtrl = DragCtrl
   If Err Then MsgBox Error$
End Sub

Open the Orders form in Design view and add the following OnMouseMove event procedure code for the Salesperson combo box:


Private Sub EmployeeID_MouseMove (Button As Integer, Shift As Integer, _
   X As Single, Y As Single)
   DropDetect Me, Me![EmployeeID], Button, Shift, X, Y
End Sub

NOTE: This control will only be a drop target.

Open the Employees form in Design view and set the Enabled property of the EmployeeID text box to Yes.

Add the following OnMouseDown event procedure code for the EmployeeID control:


Private Sub EmployeeID_MouseDown (Button As Integer, Shift As Integer, _
   X As Single, Y As Single)
   DragStart Me
End Sub

NOTE: This control will only be a drag target.

Add the following OnMouseUp event procedure code for the EmployeeID control:


Private Sub EmployeeID_MouseUp (Button As Integer, Shift As Integer, _
   X As Single, Y As Single)
   DragStop
End Sub

View the Orders form in Form view and position the form in the upper-left corner of the screen.

View the Employees form in Form view and position it on top of the Orders form, but to the right in such a way that the Salesperson combo box on the Orders form is still visible.

Hold down the mouse button in the EmployeeID text box in the Employees form, then move the mouse pointer (still holding the button down) over the Salesperson combo box on the Orders form, and then release the mouse button. RESULT: The Salesperson combo box will contain the salesperson that you dragged from the Employees form. Try moving to different Employee records and dragging the Employee ID to the Salesperson combo box.

EXAMPLE 2: Drag and Move Items from One List Box to Another List Box

The following example demonstrates how to present a list of items to a user in one list box and how to move these items back and forth to a second list box using a drag-and-drop operation.

Complete the first four steps of "EXAMPLE 1" to create the Drag and Drop procedures in the Northwind database.

Open the Customers table in Design view and add the following new field:


Field Name: Selected
Data Type : Yes/No

Create a new, blank form with the following properties:


   Form: List Box Example
   ----------------------
   Caption: ListBoxes
   RecordSelectors: No
   NavigationButtons: No
   ScrollBars: Neither

   List box
   --------------------------------------------------------------
   Name: List1
   RowSourceType: Table/Query
   RowSource: SELECT CustomerID, CompanyName FROM Customers WHERE
   Selected=False ORDER BY CompanyName;
   ColumnCount: 2
   ColumnWidths: 0
   Width: 1.5"
   Height: 1.5"

   List box
   --------------------------------------------------------------
   Name: List2
   RowSourceType: Table/Query
   RowSource: SELECT CustomerID, CompanyName FROM Customers WHERE
   Selected=True ORDER BY CompanyName;
   ColumnCount: 2
   ColumnWidths: 0
   Width: 1.5"
   Height: 1.5"

Enter the following event procedures for the List1 and List2 mouse events:


Private Sub List1_MouseDown (Button As Integer, Shift As Integer, _
   X As Single, Y As Single)
   DragStart Me
End Sub

Private Sub List1_MouseMove (Button As Integer, Shift As Integer, _
      X As Single, Y As Single)
   DropDetect Me, Me![List1], Button, Shift, X, Y
End Sub

Private Sub List1_MouseUp (Button As Integer, Shift As Integer, _
      X As Single, Y As Single)
   DragStop
End Sub

Private Sub List2_MouseDown (Button As Integer, Shift As Integer, _
      X As Single, Y As Single)
   DragStart Me
End Sub

Private Sub List2_MouseMove (Button As Integer, Shift As Integer, _
   X As Single, Y As Single)
   DropDetect Me, Me![List2], Button, Shift, X, Y
End Sub

Private Sub List2_MouseUp (Button As Integer, Shift As Integer, _
   X As Single, Y As Single)
   DragStop
End Sub

Modify the DragDrop procedure created in step 4 in "Example 1" to read as follows:


Sub DragDrop (DragFrm As Form, DragCtrl As Control, _
   DropFrm As Form, DropCtrl As Control, _
   Button As Integer, Shift As Integer, _
   X As Single, Y As Single)

   ' Which form was dropped on?
   ' It is a good idea to use the DragDrop procedure to
   ' determine which drag-and-drop operation occurred; then call
   ' appropriate code to handle the special cases.
   Select Case DropFrm.Name
      Case "List Box Example"
         ListBoxExample DragFrm, DragCtrl, DropFrm, DropCtrl, _
            Button, Shift, X, Y
      Case Else
         ' For all other cases, copy contents of Drag to Drop
         ' control.
         On Error Resume Next
         DropCtrl = DragCtrl
         If Err Then MsgBox Error$
   End Select

End Sub

Type the following new procedure in the module with the DragDrop procedure:


Sub ListBoxExample (DragFrm As Form, DragCtrl As Control, _
   DropFrm As Form, DropCtrl As Control, _
   Button As Integer, Shift As Integer, _
   X As Single, Y As Single)

   Dim DB As DAO.Database
   Dim SQL As String

   Set DB = CurrentDB()

   ' Create SQL statement to update Selected field of
   ' .. drag/dropped list box item.
   SQL = "UPDATE Customers SET Selected="

   ' Drag from List1 toggle Selected=True, List2 toggles False.
   SQL = IIF(DragCtrl.Name = "List1", SQL & "True", SQL & "False")
   ' If CTRL key not used, alter dragged value only.
   If (Shift And CTRL_MASK) = 0 Then
      SQL = SQL & " WHERE [CustomerID]='" & DragCtrl & "'"
   End If

   ' Run update query to toggle Selected field of Customer record(s).
   DB.Execute SQL

   ' Requery the list box controls to show update lists.
   DragCtrl.Requery
   DropCtrl.Requery

End Sub

View the List Box Example form in Form view, and then drag company names from one list to the other and vice versa. Press the CTRL key and drag to move ALL rows from one list to the other list.

Additional query words:


Keywords          : kbdta FmsHowto 
Version           : WINDOWS:2000
Platform          : WINDOWS 
Issue type        : kbhowto

Last Reviewed: June 10, 1999