java.lang.Object | |
↳ | java.awt.GridBagLayout |
The GridBagLayout
class is a flexible layout
manager that aligns components vertically, horizontally or along their
baseline without requiring that the components be of the same size.
Each GridBagLayout
object maintains a dynamic,
rectangular grid of cells, with each component occupying
one or more cells, called its display area.
Each component managed by a GridBagLayout
is associated with
an instance of GridBagConstraints
. The constraints object
specifies where a component's display area should be located on the grid
and how the component should be positioned within its display area. In
addition to its constraints object, the GridBagLayout
also
considers each component's minimum and preferred sizes in order to
determine a component's size.
The overall orientation of the grid depends on the container's
ComponentOrientation
property. For horizontal left-to-right
orientations, grid coordinate (0,0) is in the upper left corner of the
container with x increasing to the right and y increasing downward. For
horizontal right-to-left orientations, grid coordinate (0,0) is in the upper
right corner of the container with x increasing to the left and y
increasing downward.
To use a grid bag layout effectively, you must customize one or more
of the GridBagConstraints
objects that are associated
with its components. You customize a GridBagConstraints
object by setting one or more of its instance variables:
gridx
,
gridy
gridx = 0
,
gridy = 0
. For horizontal left-to-right layout,
a component's leading corner is its upper left. For horizontal
right-to-left layout, a component's leading corner is its upper right.
Use GridBagConstraints.RELATIVE
(the default value)
to specify that the component be placed immediately following
(along the x axis for gridx
or the y axis for
gridy
) the component that was added to the container
just before this component was added.
gridwidth
,
gridheight
gridwidth
)
or column (for gridheight
)
in the component's display area.
The default value is 1.
Use GridBagConstraints.REMAINDER
to specify
that the component's display area will be from gridx
to the last cell in the row (for gridwidth
)
or from gridy
to the last cell in the column
(for gridheight
).
Use GridBagConstraints.RELATIVE
to specify
that the component's display area will be from gridx
to the next to the last cell in its row (for gridwidth
or from gridy
to the next to the last cell in its
column (for gridheight
).
fill
GridBagConstraints.NONE
(the default),
GridBagConstraints.HORIZONTAL
(make the component wide enough to fill its display area
horizontally, but don't change its height),
GridBagConstraints.VERTICAL
(make the component tall enough to fill its display area
vertically, but don't change its width), and
GridBagConstraints.BOTH
(make the component fill its display area entirely).
ipadx
,
ipady
ipadx
pixels. Similarly, the height of
the component will be at least the minimum height plus
ipady
pixels.
insets
anchor
ComponentOrientation
property while absolute values
are not. Baseline relative values are calculated relative to the
baseline. Valid values are:
Absolute Values |
Orientation Relative Values |
Baseline Relative Values |
---|---|---|
GridBagConstraints.NORTH GridBagConstraints.SOUTH GridBagConstraints.WEST GridBagConstraints.EAST GridBagConstraints.NORTHWEST GridBagConstraints.NORTHEAST GridBagConstraints.SOUTHWEST GridBagConstraints.SOUTHEAST GridBagConstraints.CENTER (the default) |
GridBagConstraints.PAGE_START GridBagConstraints.PAGE_END GridBagConstraints.LINE_START GridBagConstraints.LINE_END GridBagConstraints.FIRST_LINE_START GridBagConstraints.FIRST_LINE_END GridBagConstraints.LAST_LINE_START GridBagConstraints.LAST_LINE_END |
GridBagConstraints.BASELINE GridBagConstraints.BASELINE_LEADING GridBagConstraints.BASELINE_TRAILING GridBagConstraints.ABOVE_BASELINE GridBagConstraints.ABOVE_BASELINE_LEADING GridBagConstraints.ABOVE_BASELINE_TRAILING GridBagConstraints.BELOW_BASELINE GridBagConstraints.BELOW_BASELINE_LEADING GridBagConstraints.BELOW_BASELINE_TRAILING |
weightx
,
weighty
weightx
) and column (weighty
),
all the components clump together in the center of their container.
This is because when the weight is zero (the default),
the GridBagLayout
object puts any extra space
between its grid of cells and the edges of the container.
Each row may have a baseline; the baseline is determined by the
components in that row that have a valid baseline and are aligned
along the baseline (the component's anchor value is one of BASELINE
, BASELINE_LEADING
or BASELINE_TRAILING
).
If none of the components in the row has a valid baseline, the row
does not have a baseline.
If a component spans rows it is aligned either to the baseline of
the start row (if the baseline-resize behavior is CONSTANT_ASCENT
) or the end row (if the baseline-resize behavior
is CONSTANT_DESCENT
). The row that the component is
aligned to is called the prevailing row.
The following figure shows a baseline layout and includes a component that spans rows:
CONSTANT_DESCENT
and has
an anchor of BASELINE
. As the baseline-resize behavior
is CONSTANT_DESCENT
the prevailing row for the panel is
row 1.
CENTER_OFFSET
and an anchor of BASELINE
.
Components positioned using one of the baseline-relative values resize
differently than when positioned using an absolute or orientation-relative
value. How components change is dictated by how the baseline of the
prevailing row changes. The baseline is anchored to the
bottom of the display area if any components with the same prevailing row
have a baseline-resize behavior of CONSTANT_DESCENT
,
otherwise the baseline is anchored to the top of the display area.
The following rules dictate the resize behavior:
OTHER
are only resized if
the baseline at the resized size fits within the display area. If
the baseline is such that it does not fit within the display area
the component is not resized.
OTHER
can only grow as tall as display height - baseline + baseline of component
.
The following figures show ten components (all buttons) managed by a grid bag layout. Figure 2 shows the layout for a horizontal, left-to-right container and Figure 3 shows the layout for a horizontal, right-to-left container.
Figure 2: Horizontal, Left-to-Right | Figure 3: Horizontal, Right-to-Left |
Each of the ten components has the fill
field
of its associated GridBagConstraints
object
set to GridBagConstraints.BOTH
.
In addition, the components have the following non-default constraints:
weightx = 1.0
weightx = 1.0
,
gridwidth = GridBagConstraints.REMAINDER
gridwidth = GridBagConstraints.REMAINDER
gridwidth = GridBagConstraints.RELATIVE
gridwidth = GridBagConstraints.REMAINDER
gridheight = 2
,
weighty = 1.0
gridwidth = GridBagConstraints.REMAINDER
Here is the code that implements the example shown above:
import java.awt.*; import java.util.*; import java.applet.Applet; public class GridBagEx1 extends Applet { protected void makebutton(String name, GridBagLayout gridbag, GridBagConstraints c) { Button button = new Button(name); gridbag.setConstraints(button, c); add(button); } public void init() { GridBagLayout gridbag = new GridBagLayout(); GridBagConstraints c = new GridBagConstraints(); setFont(new Font("SansSerif", Font.PLAIN, 14)); setLayout(gridbag); c.fill = GridBagConstraints.BOTH; c.weightx = 1.0; makebutton("Button1", gridbag, c); makebutton("Button2", gridbag, c); makebutton("Button3", gridbag, c); c.gridwidth = GridBagConstraints.REMAINDER; //end row makebutton("Button4", gridbag, c); c.weightx = 0.0; //reset to the default makebutton("Button5", gridbag, c); //another row c.gridwidth = GridBagConstraints.RELATIVE; //next-to-last in row makebutton("Button6", gridbag, c); c.gridwidth = GridBagConstraints.REMAINDER; //end row makebutton("Button7", gridbag, c); c.gridwidth = 1; //reset to the default c.gridheight = 2; c.weighty = 1.0; makebutton("Button8", gridbag, c); c.weighty = 0.0; //reset to the default c.gridwidth = GridBagConstraints.REMAINDER; //end row c.gridheight = 1; //reset to the default makebutton("Button9", gridbag, c); makebutton("Button10", gridbag, c); setSize(300, 100); } public static void main(String args[]) { Frame f = new Frame("GridBag Layout Example"); GridBagEx1 ex1 = new GridBagEx1(); ex1.init(); f.add("Center", ex1); f.pack(); f.setSize(f.getPreferredSize()); f.show(); } }
Constants | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
int | MAXGRIDSIZE | This field is no longer used to reserve arrays and keeped for backward compatibility. | |||||||||
int | MINSIZE | The smallest grid that can be laid out by the grid bag layout. | |||||||||
int | PREFERREDSIZE | The preferred grid size that can be laid out by the grid bag layout. |
Fields | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
columnWeights | This field holds the overrides to the column weights. | ||||||||||
columnWidths | This field holds the overrides to the column minimum width. | ||||||||||
comptable | This hashtable maintains the association between a component and its gridbag constraints. | ||||||||||
defaultConstraints | This field holds a gridbag constraints instance
containing the default values, so if a component
does not have gridbag constraints associated with
it, then the component will be assigned a
copy of the defaultConstraints .@serial |
||||||||||
layoutInfo | This field holds the layout information for the gridbag. | ||||||||||
rowHeights | This field holds the overrides to the row minimum heights. | ||||||||||
rowWeights | This field holds the overrides to the row weights. |
Public Constructors | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Creates a grid bag layout manager.
|
Public Methods | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Adds the specified component to the layout, using the specified
constraints object. | |||||||||||
Has no effect, since this layout manager does not use a per-component string.
| |||||||||||
Gets the constraints for the specified component.
| |||||||||||
Returns the alignment along the x axis.
| |||||||||||
Returns the alignment along the y axis.
| |||||||||||
Determines column widths and row heights for the layout grid.
| |||||||||||
Determines the origin of the layout area, in the graphics coordinate
space of the target container.
| |||||||||||
Determines the weights of the layout grid's columns and rows.
| |||||||||||
Invalidates the layout, indicating that if the layout manager
has cached information it should be discarded.
| |||||||||||
Lays out the specified container using this grid bag layout.
| |||||||||||
Determines which cell in the layout grid contains the point
specified by
(x, y) . | |||||||||||
Returns the maximum dimensions for this layout given the components
in the specified target container.
| |||||||||||
Determines the minimum size of the
parent container
using this grid bag layout. | |||||||||||
Determines the preferred size of the
parent
container using this grid bag layout. | |||||||||||
Removes the specified component from this layout.
| |||||||||||
Sets the constraints for the specified component in this layout.
| |||||||||||
Returns a string representation of this grid bag layout's values.
|
Protected Methods | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
This method is obsolete and supplied for backwards
compatability only; new code should call
adjustForGravity instead. | |||||||||||
This method is obsolete and supplied for backwards
compatability only; new code should call
arrangeGrid instead. | |||||||||||
This method is obsolete and supplied for backwards
compatability only; new code should call
getLayoutInfo instead. | |||||||||||
This method is obsolete and supplied for backwards
compatability only; new code should call
getMinSize instead. | |||||||||||
Adjusts the x, y, width, and height fields to the correct
values depending on the constraint geometry and pads.
| |||||||||||
Lays out the grid.
| |||||||||||
Fills in an instance of
GridBagLayoutInfo for the
current set of managed children. | |||||||||||
Figures out the minimum size of the
master based on the information from
getLayoutInfo . | |||||||||||
Retrieves the constraints for the specified component.
|
[Expand]
Inherited Methods | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
From class
java.lang.Object
| |||||||||||
From interface
java.awt.LayoutManager
| |||||||||||
From interface
java.awt.LayoutManager2
|
This field is no longer used to reserve arrays and keeped for backward compatibility. Previously, this was the maximum number of grid positions (both horizontal and vertical) that could be laid out by the grid bag layout. Current implementation doesn't impose any limits on the size of a grid.
The smallest grid that can be laid out by the grid bag layout.
The preferred grid size that can be laid out by the grid bag layout.
This field holds the overrides to the column weights.
If this field is non-null
the values are
applied to the gridbag after all of the columns
weights have been calculated.
If columnWeights[i]
> weight for column i, then
column i is assigned the weight in columnWeights[i]
.
If columnWeights
has more elements than the number
of columns, the excess elements are ignored - they do
not cause more columns to be created.
This field holds the overrides to the column minimum
width. If this field is non-null
the values are
applied to the gridbag after all of the minimum columns
widths have been calculated.
If columnWidths has more elements than the number of
columns, columns are added to the gridbag to match
the number of elements in columnWidth.@serial
This hashtable maintains the association between
a component and its gridbag constraints.
The Keys in comptable
are the components and the
values are the instances of GridBagConstraints
.@serial
This field holds a gridbag constraints instance
containing the default values, so if a component
does not have gridbag constraints associated with
it, then the component will be assigned a
copy of the defaultConstraints
.@serial
This field holds the layout information
for the gridbag. The information in this field
is based on the most recent validation of the
gridbag.
If layoutInfo
is null
this indicates that there are no components in
the gridbag or if there are components, they have
not yet been validated.@serial
This field holds the overrides to the row minimum
heights. If this field is non-null
the values are
applied to the gridbag after all of the minimum row
heights have been calculated.
If rowHeights
has more elements than the number of
rows, rowa are added to the gridbag to match
the number of elements in rowHeights
.@serial
This field holds the overrides to the row weights.
If this field is non-null
the values are
applied to the gridbag after all of the rows
weights have been calculated.
If rowWeights[i]
> weight for row i, then
row i is assigned the weight in rowWeights[i]
.
If rowWeights
has more elements than the number
of rows, the excess elements are ignored - they do
not cause more rows to be created.
Creates a grid bag layout manager.
Adds the specified component to the layout, using the specified
constraints
object. Note that constraints
are mutable and are, therefore, cloned when cached.
comp | the component to be added |
---|---|
constraints | an object that determines how the component is added to the layout |
IllegalArgumentException | if constraints
is not a GridBagConstraint
|
---|
Has no effect, since this layout manager does not use a per-component string.
name | the string to be associated with the component |
---|---|
comp | the component to be added |
Gets the constraints for the specified component. A copy of
the actual GridBagConstraints
object is returned.
comp | the component to be queried |
---|
Returns the alignment along the x axis. This specifies how the component would like to be aligned relative to other components. The value should be a number between 0 and 1 where 0 represents alignment along the origin, 1 is aligned the furthest away from the origin, 0.5 is centered, etc.
0.5f
to indicate centered
Returns the alignment along the y axis. This specifies how the component would like to be aligned relative to other components. The value should be a number between 0 and 1 where 0 represents alignment along the origin, 1 is aligned the furthest away from the origin, 0.5 is centered, etc.
0.5f
to indicate centered
Determines column widths and row heights for the layout grid.
Most applications do not call this method directly.
Determines the origin of the layout area, in the graphics coordinate
space of the target container. This value represents the pixel
coordinates of the top-left corner of the layout area regardless of
the ComponentOrientation
value of the container. This
is distinct from the grid origin given by the cell coordinates (0,0).
Most applications do not call this method directly.
Determines the weights of the layout grid's columns and rows. Weights are used to calculate how much a given column or row stretches beyond its preferred size, if the layout has extra room to fill.
Most applications do not call this method directly.
Invalidates the layout, indicating that if the layout manager has cached information it should be discarded.
Lays out the specified container using this grid bag layout.
This method reshapes components in the specified container in
order to satisfy the contraints of this GridBagLayout
object.
Most applications do not call this method directly.
parent | the container in which to do the layout |
---|
Determines which cell in the layout grid contains the point
specified by (x, y)
. Each cell is identified
by its column index (ranging from 0 to the number of columns
minus 1) and its row index (ranging from 0 to the number of
rows minus 1).
If the (x, y)
point lies
outside the grid, the following rules are used.
The column index is returned as zero if x
lies to the
left of the layout for a left-to-right container or to the right of
the layout for a right-to-left container. The column index is returned
as the number of columns if x
lies
to the right of the layout in a left-to-right container or to the left
in a right-to-left container.
The row index is returned as zero if y
lies above the
layout, and as the number of rows if y
lies
below the layout. The orientation of a container is determined by its
ComponentOrientation
property.
x | the x coordinate of a point |
---|---|
y | the y coordinate of a point |
Returns the maximum dimensions for this layout given the components in the specified target container.
target | the container which needs to be laid out |
---|
Determines the minimum size of the parent
container
using this grid bag layout.
Most applications do not call this method directly.
parent | the container in which to do the layout |
---|
parent
container
Determines the preferred size of the parent
container using this grid bag layout.
Most applications do not call this method directly.
parent | the container in which to do the layout |
---|
parent
container
Removes the specified component from this layout.
Most applications do not call this method directly.
comp | the component to be removed. |
---|
Sets the constraints for the specified component in this layout.
comp | the component to be modified |
---|---|
constraints | the constraints to be applied |
Returns a string representation of this grid bag layout's values.
This method is obsolete and supplied for backwards
compatability only; new code should call adjustForGravity
instead.
This method is the same as adjustForGravity
;
refer to adjustForGravity
for details
on parameters.
This method is obsolete and supplied for backwards
compatability only; new code should call arrangeGrid
instead.
This method is the same as arrangeGrid
;
refer to arrangeGrid
for details on the
parameter.
This method is obsolete and supplied for backwards
compatability only; new code should call getLayoutInfo
instead.
This method is the same as getLayoutInfo
;
refer to getLayoutInfo
for details on parameters
and return value.
This method is obsolete and supplied for backwards
compatability only; new code should call getMinSize
instead.
This method is the same as getMinSize
;
refer to getMinSize
for details on parameters
and return value.
Adjusts the x, y, width, and height fields to the correct
values depending on the constraint geometry and pads.
This method should only be used internally by
GridBagLayout
.
constraints | the constraints to be applied |
---|---|
r | the Rectangle to be adjusted |
Lays out the grid.
This method should only be used internally by
GridBagLayout
.
parent | the layout container |
---|
Fills in an instance of GridBagLayoutInfo
for the
current set of managed children. This requires three passes through the
set of children:
This method should only be used internally by
GridBagLayout
.
parent | the layout container |
---|---|
sizeflag | either PREFERREDSIZE or
MINSIZE |
GridBagLayoutInfo
for the set of childrenFigures out the minimum size of the
master based on the information from getLayoutInfo
.
This method should only be used internally by
GridBagLayout
.
parent | the layout container |
---|---|
info | the layout info for this parent |
Dimension
object containing the
minimum sizeRetrieves the constraints for the specified component.
The return value is not a copy, but is the actual
GridBagConstraints
object used by the layout mechanism.
If comp
is not in the GridBagLayout
,
a set of default GridBagConstraints
are returned.
A comp
value of null
is invalid
and returns null
.
comp | the component to be queried |
---|