A
Group
that aligns and sizes it's children.
ParallelGroup
aligns it's children in
four possible ways: along the baseline, centered, anchored to the
leading edge, or anchored to the trailing edge.
Baseline
A
ParallelGroup
that aligns it's children along the
baseline must first decide where the baseline is
anchored. The baseline can either be anchored to the top, or
anchored to the bottom of the group. That is, the distance between the
baseline and the beginning of the group can be a constant
distance, or the distance between the end of the group and the
baseline can be a constant distance. The possible choices
correspond to the
BaselineResizeBehavior
constants
CONSTANT_ASCENT
and
CONSTANT_DESCENT
.
The baseline anchor may be explicitly specified by the
createBaselineGroup
method, or determined based on the elements.
If not explicitly specified, the baseline will be anchored to
the bottom if all the elements with a baseline, and that are
aligned to the baseline, have a baseline resize behavior of
CONSTANT_DESCENT
; otherwise the baseline is anchored to the top
of the group.
Elements aligned to the baseline are resizable if they have have
a baseline resize behavior of CONSTANT_ASCENT
or
CONSTANT_DESCENT
. Elements with a baseline resize
behavior of OTHER
or CENTER_OFFSET
are not resizable.
The baseline is calculated based on the preferred height of each
of the elements that have a baseline. The baseline is
calculated using the following algorithm:
max(maxNonBaselineHeight, maxAscent + maxDescent)
, where the
maxNonBaselineHeight
is the maximum height of all elements
that do not have a baseline, or are not aligned along the baseline.
maxAscent
is the maximum ascent (baseline) of all elements that
have a baseline and are aligned along the baseline.
maxDescent
is the maximum descent (preferred height - baseline)
of all elements that have a baseline and are aligned along the baseline.
A ParallelGroup
that aligns it's elements along the baseline
is only useful along the vertical axis. If you create a
baseline group and use it along the horizontal axis an
IllegalStateException
is thrown when you ask
GroupLayout
for the minimum, preferred or maximum size or
attempt to layout the components.
Elements that are not aligned to the baseline and smaller than the size
of the ParallelGroup
are positioned in one of three
ways: centered, anchored to the leading edge, or anchored to the
trailing edge.
Non-baseline ParallelGroup
ParallelGroup
s created with an alignment other than
BASELINE
align elements that are smaller than the size
of the group in one of three ways: centered, anchored to the
leading edge, or anchored to the trailing edge.
The leading edge is based on the axis and ComponentOrientation
. For the vertical axis the top edge is
always the leading edge, and the bottom edge is always the
trailing edge. When the ComponentOrientation
is LEFT_TO_RIGHT
, the leading edge is the left edge and the
trailing edge the right edge. A ComponentOrientation
of
RIGHT_TO_LEFT
flips the left and right edges. Child
elements are aligned based on the specified alignment the
element was added with. If you do not specify an alignment, the
alignment specified for the ParallelGroup
is used.
To align elements along the baseline you createBaselineGroup
,
or createParallelGroup
with an alignment of BASELINE
.
If the group was not created with a baseline alignment, and you attempt
to add an element specifying a baseline alignment, an
IllegalArgumentException
is thrown.