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Article
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Difficulty
Rating
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4
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Groups
and
Backgrounds
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An
introduction to
Groups
A group is a
type of object that contains
other controls. It can contain
any controls - buttons, fields,
graphics, scrollbars, and eps
objects, in any combination and
number. As a result, groups are
powerful and flexible objects.
Here are some examples of what
you can do with them:
- Hide and
show multiple objects with a
single command
- Move
multiple objects with a single
command
- Creating
"panes" in a window to allow
scrolling sets of
objects
- Display
the same object or set of
objects on multiple cards (it
is possible to group a single
object)
- Create a
common script that can be used
by multiple
objects
- Automatically
track hiliting in a set of
radio buttons
- Create
tabbed menus
- Place
menus into the Mac system
menubar
When you group
objects, they get placed in
another object, which comes
complete with selection handles,
the ability to show a border, an
option to show a scrollbar etc.
Just like other objects you can
assign groups scripts and custom
properties, send messages to
them, move them etc. To edit the
properties of a group, double
click it with the pointer tool
like any other object.
However,
groups are really a unique cross
between a card and an object.
Like cards, they are attached to
the stack. Unlike cards, they can
be smaller than the window frame,
can be moved around as objects on
cards, can scroll and do most of
the things an object can do. Like
a card, their scripts get
inserted into the mesage
hierachy, just above all the
objects inside them, but before
the card.
Groups and
Backgrounds, why and whats the
difference?
Once created,
a group can be displayed on any
card in the current stack. Try it
now: create a new stack with some
objects and group them (select
them and choose "Group" from the
Edit menu), then choose
"Backgrounds..." from the "Edit"
menu. Select the group you have
created and press "Remove". The
group will dissapear from the
card (move the dialog out of the
way if you can't see the card).
You will note that the group has
appeared in the lower half of the
box. Select it, and press
"Place". It will reappear on the
current card. Now, create a few
more cards and go through each
one. You will be able to place
and remove the group on any card
in that stack using the
Backgrounds dialog. Note you can
only place a group once on any
one card. That is why the group
dissapears from the bottom half
of the dialog when you place it:
the group is still available for
placement on other cards, but
can't be placed again on the
current card.
As you will
already have noted, in MetaCard
there are two names for groups:
groups and
backgrounds. Both are used
in the Metatalk language.
Confusing? The two terms are
useful. Group refers to
group objects counted relative to
a card, background refers
to group objects relative to the
stack.
Groups
are displayed as objects on the
card. Asking for
the
number of
groups
will give you the total number of
groups on the current
card.
Backgrounds
refers to the total number of
groups in the stack. Asking for
the
number of
backgrounds
will return the total number of
unique groups in the stack,
regardless of whether or not they
are on the current (or any other)
card.
Here are two
examples. Firstly, the
backgroundNames
property returns a list of all
the groups anywhere in the stack,
whereas the
groupNames
returns a list of all the groups
that are on a particular card.
Secondly, referring to
backgrounds and groups by
number
works differently. Referring to
backgrounds by
number
works in order of creation
of any group anywhere in the
stack, but referring to groups by
number
works by using the
layer
of the group on a card.
Thus
background
1 is the
first group created anywhere in
the stack, whereas
group
1 is the
group with the lowest
layer
on the card.
You need the
two terms when using scripts to
place groups on a card. To
determine which group to place,
you need to be able to count it
relative to all the other groups
in the stack.
Manipulating
Groups
When creating
groups, it is important to
remember that the
layer
of controls in each group is
determined by their order of
selection before they are
grouped, so if you want to make
it possible for the user to tab
between controls in a group
simply select them in the
appropriate order. Of course, you
can change this order at any
point by editing the
layer
of the individual objects within
the group. Remember that the
layer
of grouped objects only refers to
their layer within the group, not
in relation to other objects in
the card. However, the number of
a grouped object refers to its
number relative to all the
objects on the card.
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TIP:
The function
the
selectedobject
returns the
name
of the currently
selected object. If
multiple objects are
selected that are not
grouped it returns the
names of all the
selected objects with
one on each line, in
order of
selection.
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To edit a
group, open its properties
palette, click the Properties
tab, and press Edit. You will go
into edit background mode, and
only the contents of the group
will be displayed - all other
objects will dissapear. To stop
editing a group, choose "Stop
editing BG" from the edit
menu.
To do this by
script:
start editing group 1
start editing background "example"
stop editing this bg
To create a
group and objects in a group by
script:
create group "My Group" -- creates a new group called "My Group"
create button "My Button" in group "My Group" -- creates a button
create fld "My Field" in group "My Group"
If you have a
nested group (a group within a
group) , it will not appear in
the Edit Background dialogue.
Edit the first level group and
then select and edit the nested
group.
You can also
add or remove groups to cards by
script:
place group "My Group" onto card 1
place background "My Group" onto card 2
remove background "My Group" from card 1
Remember that
a group is one object. So be wary
about deleting groups by
selecting and pressing the delete
key because this permanently
deletes them from every card in
the stack.
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TIP:
Setting the
selectGroupedControls
global property to
true
set the selectGroupedControls to true
allows
you select individual
controls within a group
without having to
ungroup or go into Edit
Background mode. (This
requires MetaCard
2.2.1B1 or
above.)
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Individual
controls within a group can be
deleted by script, just as if
they were separate
objects.
One
particularly useful function of
groups is to automatically make
radio buttons hilite correctly.
If you create some radio buttons
and group them, they will
automatically enforce radio
button behavior without any
scripts. It is possible to
navigate between radio buttons in
the same group using the arrow
keys on Windows and UNIX. To do
this set the
tabGroupBehavior
of the group to true. This will
also makes the tab key skip over
the whole group.
Tabbed
menus
Groups are
important for creating tab menus
and menu bars. To create a tabbed
menu create a button and using
the Button Properties dialogue,
set the style to tabbed. Set the
menu contents of the button to
the name of the different tabs
you require, and create groups
named the same as each tab. It is
easy to hide and show the groups
corresponding to each tab. Place
the following script in the
tabbed button:
on menuPick newTab, oldTab
hide group oldTab
show group newTab
end menuPick
In the above
example, the parameters passed
with the
menuPick
message (containing the name of
the tab clicked on and the name
of the tab that was previously in
front) are used to hide and show
groups with the same name as the
tabs.
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Displaying
text on multiple
cards
When
placing a group on
multiple cards, you will
often find you want to
fields such as labels to
display the same text on
each card in the stack,
while others fields
(usually for user entry)
should be editable and
display different text
on each card. Fields
which display the same
text on each card have
their
sharedText
property set to true,
and those that display
different text have
their
sharedText
property set to
false.
Similarly,
if you want to display
the same state of
hiliting in buttons and
checkboxes on each card,
set their
sharedHilite
property to true. (You
will find that if you
create labels using the
Show as Label button in
the Button Properties
dialogue their
sharedText
property is set to true,
but the default setting
for fields is
false.)
You
can sort cards by the
contents of their fields
using the
sort
command. Sorting can be
alphabetical or numeric,
and ascending or
descending. The
sort
command can be
complimented with the
identically named
mark
command and
mark
property. For example if
you want only to sort
certain cards, they can
be marked and you can
specify that only the
marked cards are
sorted.
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