The right way to handle variable heights of DBGrid rows
lazarus / 31-LCL

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j111 · 2012-05-28 17:27

Good evening!

Sample project, covered this message theme is attached to the post.
Screenshot that illustrates problem is attached too.

I went into task of displaying multiline text in DBGrid cells and have
success, but some features of the DBGrid scrolling is out of my
understanding.
If describe problem in short it lies in strange scrolling behaviour -
sometimes, selected row may be invisible for user, because it locates
under DBGrid viewport or DBGrid can fill with records only half of
visible area.

The code is very simple to understand:
1. TMyDBGrid is descendant of TCustomDBGrid, that overrides 
PrepareCanvas procedure
2. Within PrepareCanvas routine I set TextStyle with SingleLine=False
and WrodBreak=True fields and also calculate dimentions of rectangle
that can hold multiline cell text.
3. Height of text I strore in corresponding element of RowHeights
array.

All text appears multiline and well formated, but if you look at
screenshot the two facts are obvious: selected row can be displayed
under the bottom of the visible part of grid and grid itself sometimes
displayed half filled.

So, the problem now: what things should I change to have correct
scrolling.

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KpjComp · 2012-05-29 00:01

I think variable heights in a TDbGrid might be a little tricky.  This
is because as you page in the next set of records, they could all be
different heights again.  Normally you would just make the
DefaultHeight of the grid larger so that you could do multiple lines.

Another option if there are not too many records is to use a
TStringGrid/TDrawGrid, first traverse you Dataset and calculate the
heights of all records and fill the RowHeights array.  You then simply
implement a DrawCell event.

Also I think because your currently altering the RowHeights on the
PrepareCanvas virtual method, your confusing the TDbGrid and is the
reason focused records can appear partial.