How to freeze (lock) a column in the grid without use of split bar

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How to freeze (lock) a column in the grid without use of split bar

Vlad Grynchyshyn, February 8, 2002

The approach is based on a simple principle. LeftColumn property of the grid represents a column that is currently the leftmost visible column in the grid with current horizontal scrolling. As we scroll the grid horizontally, this property changes. We can assign this number to the ColumnOrder proper...

Summary

this.Columns(1).ColumnOrder = this.LeftColumn

You can use this in the Scrolled and AfterRowColChange events of the grid. However, there is a little problem with this: order of columns spoiled after few scrolling forward and back. This is because column order changes using principle "replace older column by newer on that place", so older column is placed on place of newer column. Column orders of all other columns are not changed. This causes the problem. This FAQ describes an approach that allows to organize freezing of the column and workaround most issues. The code is a very basic and simple to give the basics of the approach. Code samples could be improved to work correctly in case user change order of columns, as well as improve the logic related to the focus change.

Description

Following is a code that updates columns in grid to make first column always leftmost. Use it in the Scrolled event when grid is scrolled horizontally and in the AfterRowColChange event when active column is changed in the grid.

	local i
	if this.columns(1).ColumnOrder < this.LeftColumn
		&& we scroll forward
		for i=this.columns(1).ColumnOrder to this.LeftColumn-1
			this.columns(1).ColumnOrder = this.columns(1).ColumnOrder + 1
		endfor
	else
		&& we scroll backward
		for i=this.LeftColumn+1 to this.columns(1).ColumnOrder
			this.columns(1).ColumnOrder = this.columns(1).ColumnOrder - 1
		endfor
	endif

The above code is very simple because it is written only for the column 1 and only one column frozen. The approach change ColumnOrder of the column by 1. This cause correct moving of column to required place like if you move the column by dragging it by header. This save the original order of columns and solve any problems with confusing order change after scrolling. Use this code in the AfterRowColChange event (when column changed) or in the Scrolled event (when grid is scrolled horizontally, in other words, when nDirection parameter of the Scrolled event is greater or equal 4). For more complex case (more than one column) you will require to do similar things. For example, following is for 2 columns:

	local i, lnCurrOrder
	m.lnCurrOrder = this.columns(1).ColumnOrder
	if this.columns(1).ColumnOrder < this.LeftColumn
		&& we scroll forward
		for i=m.lnCurrOrder to this.LeftColumn-1
			this.columns(2).ColumnOrder = this.columns(2).ColumnOrder + 1
		endfor
		for i=m.lnCurrOrder to this.LeftColumn-1
			this.columns(1).ColumnOrder = this.columns(1).ColumnOrder + 1
		endfor
	else
		&& we scroll backward
		for i=this.LeftColumn+1 to m.lnCurrOrder
			this.columns(1).ColumnOrder = this.columns(1).ColumnOrder - 1
		endfor
		for i=this.LeftColumn+1 to m.lnCurrOrder
			this.columns(2).ColumnOrder = this.columns(2).ColumnOrder - 1
		endfor
	endif

Finally, when doing manipulations with column objects on the form, the current focused column might be lost. The workaround for this is to remember current focused column and set the focus back after moving "locked" columns. So, wrap the column(s) moving code (above sample code) into the following code:

	lnCol = this.ActiveColumn
	lnColToFocus = 0
	if lnCol > 0
		for i=1 to this.ColumnCount
			if this.columns(m.i).ColumnOrder = m.lnCol
				lnColToFocus = m.i
				exit
			endif
		endfor
	endif

        * Check if we do not need to set focus to the last column in grid
        * This will happen when we did not focused column explicitly by 
        * mouse and pressed either Shift+TAB, left arrow key or Ctrl+left 
        * arrow key. In the last condition we check if column focused is 
        * the locked column. When you have 2 columns, you should check for 
        * both (for example, 
        * "AND (m.lnColToFocus = 1 OR m.lnColToFocus = 2)")
	if not MDOWN() AND inlist(lastkey(),15,19,26) AND (m.lnColToFocus = 1)
			this.Columns(this.ColumnCount).SetFocus
			m.lnColToFocus = this.ColumnCount
	endif

* ....... Put here code from previous samples

	if lnColToFocus > 0
		if this.Columns(m.lnColToFocus).ColumnOrder > this.LeftColumn
			this.Columns(m.lnColToFocus).SetFocus
		else
			* Determine the next column after locked and focus it
			for i=1 to this.ColumnCount
				if this.columns(m.i).ColumnOrder = this.Columns(1).ColumnOrder + 2
					lnColToFocus = m.i
					exit
				endif
			endfor
			this.Columns(m.lnColToFocus).SetFocus
		endif
	endif

The side effect of the above code is that "TAB" key pressing in last column when it is active will cause moving to the first column that is not locked. This is a good thing also, because usually locked column is used as information column when others are for data entry. To do opposite (SHIFT+TAB in the first not locked column will focus the last column), we should add some code in the AfterRowColChange event to fix the active column - appropriate section of the code in above sample is marked by comment "Check if we do not need to set focus to the last column in grid". There is also a problem - when scrolling horizontally and focused column goes out of scrolled area, we just cannot restore active column because this will scroll the grid back. In such case it is good idea to set the focus to the column just after locked column(s) in current scrolling. This column will have next ColumnOrder value after the locked column. This workaround is after the comment "Determine the next column after locked and focus it".

Vlad Grynchyshyn, Soft Serve
Vlad Grynchyshyn is senior developer and project manager at the Ukrainian company "Soft Serve Ltd.", that provides custom-developed software solutions in several areas with use of wide range of development tools and languages. Vlad works in the MS Solutions department of the company, and has experience working with many MS development tools, components, utilities and documentation. Most experience is related to Visual FoxPro, MS SQL Server, Visual Studio and Visual Basic. He is active member of Visual FoxPro and SQL Server community, author of several articles for Universal Thread WEB site and other VFP community forums. He was MS MVP 2001-2002. He has a MS MCP certificate in Visual FoxPro area.

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