LayoutManager
, LayoutManager2
, Serializable
public class GridBagLayout extends Object implements LayoutManager2, Serializable
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:
GridBagConstraints.gridx
, GridBagConstraints.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. GridBagConstraints.gridwidth
, GridBagConstraints.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
). GridBagConstraints.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). GridBagConstraints.ipadx
, GridBagConstraints.ipady
ipadx
pixels. Similarly, the height of the component will be at least the minimum height plus ipady
pixels. GridBagConstraints.insets
GridBagConstraints.anchor
ComponentOrientation
property while absolute values are not. Baseline relative values are calculated relative to the baseline. Valid values are: 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
GridBagConstraints.weightx
, GridBagConstraints.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:
This layout consists of three components:
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(); } }
Modifier and Type | Field | Description |
---|---|---|
double[] |
columnWeights |
This field holds the overrides to the column weights. |
int[] |
columnWidths |
This field holds the overrides to the column minimum width. |
protected Hashtable |
comptable |
This hashtable maintains the association between a component and its gridbag constraints. |
protected GridBagConstraints |
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 . |
protected GridBagLayoutInfo |
layoutInfo |
This field holds the layout information for the gridbag. |
protected static final int |
MAXGRIDSIZE |
This field is no longer used to reserve arrays and kept for backward compatibility. |
protected static final int |
MINSIZE |
The smallest grid that can be laid out by the grid bag layout. |
protected static final int |
PREFERREDSIZE |
The preferred grid size that can be laid out by the grid bag layout. |
int[] |
rowHeights |
This field holds the overrides to the row minimum heights. |
double[] |
rowWeights |
This field holds the overrides to the row weights. |
Constructor | Description |
---|---|
GridBagLayout() |
Creates a grid bag layout manager. |
Modifier and Type | Method | Description |
---|---|---|
void |
addLayoutComponent |
Adds the specified component to the layout, using the specified constraints object. |
void |
addLayoutComponent |
Has no effect, since this layout manager does not use a per-component string. |
protected void |
adjustForGravity |
Adjusts the x, y, width, and height fields to the correct values depending on the constraint geometry and pads. |
protected void |
AdjustForGravity |
Adjusts the x, y, width, and height fields to the correct values depending on the constraint geometry and pads. |
protected void |
arrangeGrid |
Lays out the grid. |
protected void |
ArrangeGrid |
This method is obsolete and supplied for backwards compatibility only; new code should call arrangeGrid instead. |
GridBagConstraints |
getConstraints |
Gets the constraints for the specified component. |
float |
getLayoutAlignmentX |
Returns the alignment along the x axis. |
float |
getLayoutAlignmentY |
Returns the alignment along the y axis. |
int[][] |
getLayoutDimensions() |
Determines column widths and row heights for the layout grid. |
protected GridBagLayoutInfo |
getLayoutInfo |
Fills in an instance of GridBagLayoutInfo for the current set of managed children. |
protected GridBagLayoutInfo |
GetLayoutInfo |
This method is obsolete and supplied for backwards compatibility only; new code should call getLayoutInfo instead. |
Point |
getLayoutOrigin() |
Determines the origin of the layout area, in the graphics coordinate space of the target container. |
double[][] |
getLayoutWeights() |
Determines the weights of the layout grid's columns and rows. |
protected Dimension |
getMinSize |
Figures out the minimum size of the parent based on the information from getLayoutInfo . |
protected Dimension |
GetMinSize |
This method is obsolete and supplied for backwards compatibility only; new code should call getMinSize instead. |
void |
invalidateLayout |
Invalidates the layout, indicating that if the layout manager has cached information it should be discarded. |
void |
layoutContainer |
Lays out the specified container using this grid bag layout. |
Point |
location |
Determines which cell in the layout grid contains the point specified by (x, y) . |
protected GridBagConstraints |
lookupConstraints |
Retrieves the constraints for the specified component. |
Dimension |
maximumLayoutSize |
Returns the maximum dimensions for this layout given the components in the specified target container. |
Dimension |
minimumLayoutSize |
Determines the minimum size of the parent container using this grid bag layout. |
Dimension |
preferredLayoutSize |
Determines the preferred size of the parent container using this grid bag layout. |
void |
removeLayoutComponent |
Removes the specified component from this layout. |
void |
setConstraints |
Sets the constraints for the specified component in this layout. |
String |
toString() |
Returns a string representation of this grid bag layout's values. |
protected static final int MAXGRIDSIZE
protected static final int MINSIZE
protected static final int PREFERREDSIZE
protected Hashtable<Component,GridBagConstraints> comptable
comptable
are the components and the values are the instances of GridBagConstraints
.protected GridBagConstraints defaultConstraints
defaultConstraints
.protected GridBagLayoutInfo layoutInfo
layoutInfo
is null
this indicates that there are no components in the gridbag or if there are components, they have not yet been validated.public int[] columnWidths
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.public int[] rowHeights
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, rows are added to the gridbag to match the number of elements in rowHeights
.public double[] columnWeights
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.public double[] rowWeights
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.public GridBagLayout()
public void setConstraints(Component comp, GridBagConstraints constraints)
comp
- the component to be modifiedconstraints
- the constraints to be appliedpublic GridBagConstraints getConstraints(Component comp)
GridBagConstraints
object is returned.comp
- the component to be queriedprotected GridBagConstraints lookupConstraints(Component comp)
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 queriedpublic Point getLayoutOrigin()
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.public int[][] getLayoutDimensions()
Most applications do not call this method directly.
public double[][] getLayoutWeights()
Most applications do not call this method directly.
public Point location(int x, int y)
(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 pointy
- the y coordinate of a pointpublic void addLayoutComponent(String name, Component comp)
addLayoutComponent
in interface LayoutManager
name
- the string to be associated with the componentcomp
- the component to be addedpublic void addLayoutComponent(Component comp, Object constraints)
constraints
object. Note that constraints are mutable and are, therefore, cloned when cached.addLayoutComponent
in interface LayoutManager2
comp
- the component to be addedconstraints
- an object that determines how the component is added to the layoutIllegalArgumentException
- if constraints
is not a GridBagConstraint
public void removeLayoutComponent(Component comp)
Most applications do not call this method directly.
removeLayoutComponent
in interface LayoutManager
comp
- the component to be removed.public Dimension preferredLayoutSize(Container parent)
parent
container using this grid bag layout. Most applications do not call this method directly.
preferredLayoutSize
in interface LayoutManager
parent
- the container in which to do the layoutparent
containerpublic Dimension minimumLayoutSize(Container parent)
parent
container using this grid bag layout. Most applications do not call this method directly.
minimumLayoutSize
in interface LayoutManager
parent
- the container in which to do the layoutparent
containerpublic Dimension maximumLayoutSize(Container target)
maximumLayoutSize
in interface LayoutManager2
target
- the container which needs to be laid outpublic float getLayoutAlignmentX(Container parent)
getLayoutAlignmentX
in interface LayoutManager2
parent
- the target container0.5f
to indicate centeredpublic float getLayoutAlignmentY(Container parent)
getLayoutAlignmentY
in interface LayoutManager2
parent
- the target container0.5f
to indicate centeredpublic void invalidateLayout(Container target)
invalidateLayout
in interface LayoutManager2
target
- the target containerpublic void layoutContainer(Container parent)
GridBagLayout
object. Most applications do not call this method directly.
layoutContainer
in interface LayoutManager
parent
- the container in which to do the layoutpublic String toString()
protected GridBagLayoutInfo getLayoutInfo(Container parent, int sizeflag)
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 containersizeflag
- either PREFERREDSIZE
or MINSIZE
GridBagLayoutInfo
for the set of childrenprotected GridBagLayoutInfo GetLayoutInfo(Container parent, int sizeflag)
getLayoutInfo
instead. Fills in an instance of GridBagLayoutInfo
for the current set of managed children. This method is the same as getLayoutInfo
; refer to getLayoutInfo
description for details.parent
- the layout containersizeflag
- either PREFERREDSIZE
or MINSIZE
GridBagLayoutInfo
for the set of childrenprotected void adjustForGravity(GridBagConstraints constraints, Rectangle r)
GridBagLayout
.constraints
- the constraints to be appliedr
- the Rectangle
to be adjustedprotected void AdjustForGravity(GridBagConstraints constraints, Rectangle r)
This method is obsolete and supplied for backwards compatibility only; new code should call adjustForGravity
instead. This method is the same as adjustForGravity
constraints
- the constraints to be appliedr
- the Rectangle
to be adjustedprotected Dimension getMinSize(Container parent, GridBagLayoutInfo info)
getLayoutInfo
. This method should only be used internally by GridBagLayout
.parent
- the layout containerinfo
- the layout info for this parentDimension
object containing the minimum sizeprotected Dimension GetMinSize(Container parent, GridBagLayoutInfo info)
getMinSize
instead. This method is the same as getMinSize
parent
- the layout containerinfo
- the layout info for this parentDimension
object containing the minimum sizeprotected void arrangeGrid(Container parent)
GridBagLayout
.parent
- the layout containerprotected void ArrangeGrid(Container parent)
arrangeGrid
instead. This method is the same as arrangeGrid
parent
- the layout container
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