How to Set Up a Grid as a Destination for Drag and Drop

• Microsoft Visual FoxPro for Windows, versions 3.0 and 3.0b

SUMMARY

By default, if a grid is used for the destination of a drag and drop operation, the DragDrop method of the grid is called. This does not allow dropping into an individual grid cell, because the DragDrop method of the cell control is never called. This article shows how to calculate the destination cell coordinates, and call the DragDrop method of the appropriate destination.

MORE INFORMATION

The following code demonstrates how a grid can be set up as the destination of a drag and drop operation. This example uses the Customer table from the \VFP\Samples\Data\Testdata database.

Step-by-Step Example

1. Run the following commands in the Command window to create a table to use as the RecordSource of the grid that will be the destination of the drag and drop operation.

   USE HOME()+"samples\data\customer.dbf" COPY TO cust_tmp.dbf

2. Create a new form. Add the Testdata!Customer and Cust_tmp tables to the Data Environment of the form.

3. Place the source grid on the form by dragging the Customer table from the Data Environment. Set the ColumnCount of this grid to 5.

4. Place the following code in the MouseDown event for the text box in each of the columns in the source grid:

      THIS.Drag(1)    && Starts Drag
   
   

5. Place the following code in the MouseUp event for the text box in each of the columns in the source grid:

      THIS.Drag(0)    && Ends Drag if mouse button is released
   
   

6. Place the destination grid on the form by dragging the Cust_tmp table from the Data Environment. Set its ColumnCount property to 5.

7. Place the following code in the DragDrop event for the destination grid. The LPARAMETERS statement will already be present.

   LPARAMETERS oSource, nXCoord, nYCoord PRIVATE nPrevColwidths, nGridLeftwall, nGridRightwall, nRowlevel, ;

         nGridBottomEdge, nColCount
   

   * Check destination grid for DeleteMark and RecordMark nGridLeftWall=1+THIS.Left+IIF(THIS.DeleteMark and THIS.RecordMark,18, ;

         IIF(THIS.DeleteMark or THIS.RecordMark,9,0))
   

   * Check destination grid for Vertical Scroll bar nGridRightWall=THIS.Left+THIS.Width-IIF(THIS.ScrollBars>1,14,0)

   * Check destination grid for Horizontal Scroll bar nGridBottomEdge=THIS.Top+THIS.Height-IIF(THIS.ScrollBars=1 or ;

         THIS.ScrollBars=3, 12 ,0)
   

   * Hold sum of ColumnWidths of columns to left of current column nPrevColwidths=0

   * Find out which destination row nRowlevel=CEILING((nYcoord-THIS.Top-THIS.HeaderHeight)/THIS.RowHeight)

   * Necessary if grid RecordSource table is not currently selected SELECT EVAL('THIS.RecordSource')

   * Loop through all visible columns FOR ni=THIS.LeftColumn to THIS.ColumnCount

         * Determine if current column is drop destination
         IF BETWEEN(nXCoord, nGridLeftwall+nPrevColWidths, nGridLeftwall + ;
   

            nPrevColwidths+THIS.Columns(ni).Width) and nRowlevel>0 and ;
               nYCoord < nGridBottomEdge and nXCoord < nGridRightWall
   
            * If correct column, call DragDrop of textbox in the column
            THIS.Columns(ni).Text1.DragDrop(oSource,0,nYCoord, ;
               ni+1-THIS.LeftColumn,nRowlevel)
            EXIT       && After drop, no need to check additional columns
   
         ENDIF
   
         * Add width of current column to sum of widths of previous columns
         * and proceed to calculate if next column is drop destination
         nPrevColWidths=nPrevColWidths+THIS.Columns(ni).Width
      ENDFOR
   
   

8. Place the following code in the DragDrop event's method code for the text box control in each of the columns of the destination grid (Note the two added parameters in the LPARAMETERS statement).

   LPARAMETERS oSource, nXCoord, nYCoord, nDropCol, nDropRow * Activate cell which is destination for drop THIS.PARENT.PARENT.ActivateCell(nDropRow,nDropCol)

   * Replace ControlSource field with value of dragged object REPLACE (THIS.ControlSource) WITH oSource.Value

9. Run the form, and drag from the source grid to the destination grid. The value present in the source grid cell will appear in the destination grid cell.

Notes

1. The form ScaleMode property needs to be 3 - Pixels for the determination of the destination column and row to work properly.

2. If the data types of the source and destination are different, a "Data type mismatch" error will occur.

3. This example uses a text box in a grid column as the source of the drag operation, but a text box on a form will work as well, as should any source where the data type is the same as that of the destination.