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Frequently Asked Questions

ID: 8001
Created on: January 26, 2001 06:46
Updated on: April 22, 2010 21:31

How to refresh grid properly after sorting
I have seen many questions about sorting of a grid by clicking on its header and proper refreshing of grid after sorting. There is a reliable way to sort (index) grid cursor and properly refresh the grid without change of the record number AND with very good looking. I made this in my grid class and tested it already 2 years so far.

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Vlad Grynchyshyn
Soft Serve

Note that the way I used has a requirement for the grid cursor - it should not contain changes or may contain, but only in table buffering mode. This is because the changes will be automatically updated when the record pointer moved for cursors in the row buffering mode. I prohibit any sorting until the user saves changes - a solution on the interface level.

Following is the code from my grid class commented and fixed to do not confuse by details of my framework:

* Grid.RefreshAfterSorting
* Used grid custom properties:
* lSorting - flag that indicates sorting refreshing, so all activity related with row
*            change in grid should be disabled for the duration of this routine
* nRecno - stores record number of current row in grid. This property should be populated
*          in the AfterRowColChange event by record number each time record number changed
* lInit - flag, should be .T. when Init method is running

lparameters poColumn
* column reference should be passed of column being sorted
* called internally only as event from the column header after sorting
with this
	.lSorting = .T. 
        && above flag used in the AfterRowColChange and other grid events to do not fire 
        && any code during running of this method. This method might cause weird record
        && moving by grid when sorted, so anyway it is required. We will force record
        && moveng too for better refreshing.

	local lcOldArea, lcGridAlias
	m.lcOldArea = select(0)
	m.lcGridAlias = this.RecordSource
	select (m.lcGridAlias)

	* store 'real' grid position, this is needed because it might change in the
        * next chapter
	local nOldRecNo
	m.nOldRecNo = .nRecno && nRecNo - property that updated in AfterRowColChange event
                              && of grid in AfterRowColChange event flag lSorting prevents
                              && change of this property

	&& restore row position - it might be changed during indexing and cell activation

        && after refresh after sorting you can see grid shows, for example, last row only,
        && when really it contains 3 rows and all fit into grid. This is a problem we going
        && to solve by following code lines

	* this must be BEFORE any refresh of grid
	if between(m.nOldRecNo,1,reccount())
		LOCATE && FOR .T., same as 'go top', but works more quickly for
                       && filtered data

	&& activate cell that is appropriate to sorting column,
        && so grid will not scroll out from sorting column. When we do not do this, after
        && click on the header, grid will scroll to current cell (column) focused, that
        && might hide (scroll out) column that is just sorted - looks confusing.
	if !.lInit && flag that is .T. when Init method is running.
		if between(m.nOldRecNo,1,reccount())
			go (m.nOldRecNo)
                && during Grid Init, however, we should not do this because SetFocus will
                && cause error. Just refresh it. This is needed to check for case when we
                && want to restore grid sorting when form loads from user preferenses
		if between(m.nOldRecNo,1,reccount())
			go (m.nOldRecNo)

	select (m.lcOldArea)
	DOEVENTS && this is required before any other actions to correctly refresh grid
                 && and do not move record pointer weirdly
	.lSorting = .F.
It is also recommended to use thisform.LockScreen to prevent the grid flashing - hide all grid refreshing from users, so they will see just the results.

When screen is locked, first Refresh commands are required just for repositioning current grid scrolling position. As a result, the work grid does for displaying (drawing) records gone for nothing. In cause you have really a lot of things placed in the Dynamic* properties of the grid columns to organize some fancy things, like highlighting of the current record or colour grid cells by different colours appropriate to some conditions in the data records, it will look quite slow when doing multiple refreshes like in this article. To speed it up, use very simple approach: Before first refreshes just after locking the screen, backup all Dynamic* settings of all columns in some array or additional properties, then clear them all. Just before the last refresh restore all Dynamic* property values. This speeds up the total time of above approach running.


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