Q185497: HOWTO: Using GridHitTest() with OLE Drag and Drop
Article: Q185497
Product(s): Microsoft FoxPro
Version(s): WINDOWS:6.0
Operating System(s):
Keyword(s):
Last Modified: 12-AUG-1999
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The information in this article applies to:
- Microsoft Visual FoxPro for Windows, version 6.0
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SUMMARY
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OLE Drag and Drop is a new feature in Visual FoxPro 6.0. This article shows how
to make use of the new GridHitTest() function with OLE Drag and Drop to drag
text from a text box and drop it into a cell in a grid. Changing the mouse
pointer while dragging the text is also featured in this article. This article
does not cover all scenarios when dragging text into a grid. It is provided to
allow developers to get a start in working with OLE Drag and Drop.
This article does not cover the background for OLE Drag and Drop. For more
information on OLE Drag and Drop, please see Chapter 31: Interoperability and
the Internet in the Microsoft Visual FoxPro "Programmer's Guide," version 6.0.
MORE INFORMATION
================
Follow the steps below to create a sample form that allows text to be dragged
out of a text box control and dropped into a cell in a grid.
1. Create a table for use with the grid. The following code can be used:
** Make table
CREATE TABLE gridtest (color c(10), fruit c(15), quantity i)
INSERT INTO gridtest VALUES ("Red","Apple",5)
INSERT INTO gridtest VALUES ("Blue","Pear",10)
INSERT INTO gridtest (fruit) VALUES ("Peach")
INSERT INTO gridtest (COLOR) VALUES ("Green")
INSERT INTO gridtest (quantity) VALUES (7)
INSERT INTO gridtest (COLOR,fruit) VALUES ("Black","Blackberry")
INSERT INTO gridtest (COLOR,quantity) VALUES("Orange",3)
INSERT INTO gridtest (fruit,quantity) VALUES ("Orange",8)
INSERT INTO gridtest (fruit,COLOR) VALUES ("Banana","Indigo")
2. Create a new form. Save the form as Gridodd.scx.
3. Add the gridtest table created in step 1 to the data environment of the form.
4. Drag the table from the data environment to the form. It should create a grid
when dropped onto the form. Resize the form and grid as desired.
5. Add a text box control to the form. Set the OLEDragMode property to 1 -
Automatic.
6. Place the following code in the text box's OLEGiveFeedback event. Note that
the LPARAMETERS line should already be there by default.
LPARAMETERS nEffect, eMouseCursor
IF nEffect=0
eMouseCursor=12 && the no drop circle with line
ELSE
eMouseCursor="bullseye.cur"
ENDIF
7. Copy the Bullseye.cur file from Visual Studio\Common\Graphics\Cursors folder
to the folder where the form and table are saved. The HOME(4) function can be
used to find the path to the Visual Studio\Common\Graphics folder. The
following command can be used in the Visual FoxPro Command window to copy the
file to the current default folder:
COPY FILE HOME(4)+"Cursors\bullseye.cur" TO SYS(5)+SYS(2003)
8. Set the OLEDropMode property of the grid to 1 - Enabled.
9. Add the following code to the OLEDragOver event of the grid. Note that the
LPARAMETERS line should already be there by default.
LPARAMETERS oDataObject, nEffect, nButton, nShift, nXCoord, ;
nYCoord, nState
LOCAL nWhere
nWhere=0
IF This.GridHitTest(nXCoord,nYCoord,@nWhere)
IF nWhere=3 && over a grid cell
nEffect=3
ELSE
nEffect=0 && if not over a grid cell, can't drop
ENDIF
ENDIF
10. Add the following code to the OLEDragDrop event of the grid. Note that the
LPARAMETERS line should already be there by default.
LPARAMETERS oDataObject, nEffect, nButton, nShift, nXCoord, nYCoord
LOCAL nOperation, cText, nWhere, nRelRow, nRelCol
IF nShift=2 && Control key is down
nOperation=1 && DropEffect_Copy
ELSE
nOperation=2 && DropEffect_Move
ENDIF
IF This.GridHitTest(nXCoord,nYCoord,@nWhere,@nRelRow,@nRelCol)
IF nWhere=3 && over a grid cell
This.ActivateCell(nRelRow,nRelCol)
ENDIF
ENDIF
IF oDataObject.GetFormat(1) && CF_TEXT
cText=oDataObject.GetData(1)
This.Columns(nRelCol).Text1.Value=cText
NODEFAULT
ENDIF
nEffect=nOperation && nEffect gets passed to OLECompletDrag
11. Save and run the form.
12. Enter some text in the text box, select it and drag the text into one of the
grid cells. Also, try holding down the CTRL key while dragging. Without
holding down the CTRL key, the text moves, with the CTRL key, the text
copies and is in the text box in addition to the grid.
Briefly, what happens when the text is dragged out of the text box and over the
grid is this:
1. The form's OLEDropMode property is set to 0 - Disabled so the mouse pointer
stays the default "no drop" pointer. However, the grid's OLEDropMode property
is set to 1 - Enabled.
2. When the mouse with the data is moved over the grid, the grid's OLEDragOver
event fires. Within the OLEDragOver event, the GridHitTest function fires.
When it returns a three (3), which means that the mouse is over a grid cell,
the text box's OLEGiveFeedback tells FoxPro to change the mouse pointer to
the bullseye cursor. This lets the user know that the text can be dropped
there.
3. When the user drops the text on top of a grid cell, the grid's OLEDragDrop
event fires. Within this event, the GridHitTest fires again with the
coordinates of the mouse being passed to the event. GridHitTest returns, by
reference, whether or not the mouse is over a grid cell as well as the
relative row and column values for the grid. These are then used in the
grid's ActivateCell method to select the grid cell that the mouse is over.
4. Now that FoxPro knows what grid cell the mouse is over and has activated it,
it checks to see if there is text data in the Data Object. The
oDataObject.GetFormat(1) line of code in the grid's OLEDragDrop event does
this. If there is text data, it is obtained and stored to a variable using
the Data Object's GetData() method. The value property of the text box
control in the current grid cell is then set to the variable containing the
data just obtained from the Data Object.
5. Within the grid's OLEDragDrop event, the nShift parameter is checked to see
if any of the modifier keys are held down. In this example, there is a check
for the CTRL key. If the CTRL key is down, the nEffect output parameter is
set to 1, which means copy. If the CTRl key is not held down, nEffect is set
to 2, which means move.
6. The nEffect output parameter of the grid's OLEDragDrop event is passed into
the text box's OLECompleteDrag event. In this case, there is no code in the
text box's OLECompleteDrag so the default behavior takes place. Move deletes
the data from the text box, copy leaves it in the text box.
REFERENCES
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Microsoft Visual FoxPro "Programmer's Guide," version 6.0, Chapter 31:
Interoperability and the Internet. The section on OLE Drag and Drop.
Microsoft Visual FoxPro Help, 6.0: search on: "GridHitTest()";
"OLEDropMode"; "OLEDragDrop"; "OLECompleteDrag"; "OLEDragOver"
Additional query words: FxprgClassoop FxprgGrid kbvfp600
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Keywords :
Technology : kbVFPsearch kbAudDeveloper kbVFP600
Version : WINDOWS:6.0
Issue type : kbhowto
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