HOWTO: Using GridHitTest() with OLE Drag and Drop

• Microsoft Visual FoxPro for Windows, version 6.0

SUMMARY

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.

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

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

Keywords :
Version : WINDOWS:6.0
Platform : WINDOWS
Issue type : kbhowto