[Lazarus] ListView and autosize

[Hans-Peter Diettrich]

Vincent Snijders schrieb:
> 2011/5/9 Hans-Peter Diettrich <DrDiettrich1 at aol.com>:
>> How would you tell the users, that a column width of -2 means auto-expand?
> 
> http://msdn.microsoft.com/en-us/library/bb761163%28v=vs.85%29.aspx
> 
> The value of LVSCW_AUTOSIZE_USEHEADER is -2.

Okay, that's a Windows specific convention. Unfortunately it is not 
documented in a way that allows to implement it for other widgetsets. 
E.g. what shall happen if a user tries to apply it to multiple columns? 
What size should be assigned to the previous auto-expand column, when 
another column becomes auto-expand?


A proper implementation IMO should implement the AutoSize (and other) 
features in a widgetset independent way, e.g. in the TWSCustomListView 
base class, for use in all widgetsets that don't support a feature 
natively. This implementation defines what behaviour the user can expect 
in every widgetset, as long as according documentation is missing.

In a portable environment there exist chances for incompatible 
implementations of similar or essentially the same features, in 
different widgetsets. The use of widgetset-specific features should be 
allowed, of course, at the risk of the user; this means that the boolean 
TListColumn.AutoSize property should be retyped, e.g. into an enum. 
Otherwise it would be a good idea to add portable properties to the 
ListView control itself, with an also portable implementation.

One such portable property could be what I tried to implement, an 
automatic expansion of the rightmost column. A more flexible 
implementation could specify a column that should be auto-expanded (kind 
of alClient), with proper handling of column reordering. In any case the 
implementation (calculation of concrete column widths) can reside 
entirely in the control, without any special widgetset support.

DoDi