On Wed, 7 Apr 2010, Hans-Peter Diettrich wrote:
Michael Van Canneyt schrieb:
IMO it's quite simple. A layout affects the position of child controls
inside a container control, nothing else. Borders, Constraints and
Autosize are general properties of all controls, which must be handled
in/by the control itself.
I agree for Constraints, but not the other two.
It is in contradiction with what Mattias said, where he claimed that
when doing layouting you must always work inside-out and outside-in.
Borderspacing IS used when layouting: it determines the available space
for childs inside/outside the control.
The control determines its client extent from given bounds, by taking into
account its specified border style. A layout manager has no idea of such
borders, bevels etc., and also not of the visible rectangle of a
TScrollingWindowControl.
From
http://wiki.lazarus.freepascal.org/Autosize_/_Layout#Align_and_BorderSpacing
"The space of BorderSpacing and of the parent's ChildSizing is applied to
aligned controls. The memo below has Align=alClient"
BorderSpacing has nothing to do with border style or bevels. It is an EXTRA
margin. Border style and bevels determine the ClientRect of a control, and
as Mattias said, they must be queried from the control itself.
Autosize as well: if autosize is true, then the size of the control
changes, and therefor the layout internal to the control, but also
externally. Hence it belongs in the layouter.
In the simplest case the layouter has not to care about autosize at all. The
control determines its required extent, based on e.g. font size and
nationalized text, and reports it as its required extent. There is nothing
beyond that extent that a layout manager has to know about.
Only when a control can adopt itself to different *given* extents, by e.g.
breaking its content into multiple lines, a layout manager has to split the
available extent into zones for the client controls. Such a layout manager
would accept an extent in one direction, and calculate the resulting extent
in the other direction, or spread the client controls evenly. This is a
different behaviour from the beforementioned Autosize of controls with no
child controls.
AutoSize for a panel explicitly is about child controls, and therefor
layouting.
Unfortunately Borland used AutoSize for 2 different things:
- Resize control to accomodate child controls (as e.g. in TPanel)
- To accomodate for 'native content', such as in TLabel.
They should have been separate properties. I am talking only about
the first one. The second one, obviously, is only necessary for the
control itself.
IMHO a control needs only 5 properties: top/left/width,height and
constraints. All the rest is layouting.
You mean that every control should have borders or bevels, as specified by
the layout manager? How should such a manager know about different border
styles for its client controls?
It does not need to. ClientRect is used for this.
Michael.
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