Class FormLayout
FormAttachments
to optionally configure the left, top, right and bottom edges of
each child.
The following example code creates a FormLayout
and then sets
it into a Shell
:
Display display = new Display (); Shell shell = new Shell(display); FormLayout layout = new FormLayout(); layout.marginWidth = 3; layout.marginHeight = 3; shell.setLayout(layout);
To use a FormLayout
, create a FormData
with
FormAttachment
for each child of Composite
.
The following example code attaches button1
to the top
and left edge of the composite and button2
to the right
edge of button1
and the top and right edges of the
composite:
FormData data1 = new FormData(); data1.left = new FormAttachment(0, 0); data1.top = new FormAttachment(0, 0); button1.setLayoutData(data1); FormData data2 = new FormData(); data2.left = new FormAttachment(button1); data2.top = new FormAttachment(0, 0); data2.right = new FormAttachment(100, 0); button2.setLayoutData(data2);
Each side of a child control can be attached to a position in the parent
composite, or to other controls within the Composite
by
creating instances of FormAttachment
and setting them into
the top, bottom, left, and right fields of the child's FormData
.
If a side is not given an attachment, it is defined as not being attached
to anything, causing the child to remain at its preferred size. If a child
is given no attachment on either the left or the right or top or bottom, it is
automatically attached to the left and top of the composite respectively.
The following code positions button1
and button2
but relies on default attachments:
FormData data2 = new FormData(); data2.left = new FormAttachment(button1); data2.right = new FormAttachment(100, 0); button2.setLayoutData(data2);
IMPORTANT: Do not define circular attachments. For example, do not attach
the right edge of button1
to the left edge of button2
and then attach the left edge of button2
to the right edge of
button1
. This will over constrain the layout, causing undefined
behavior. The algorithm will terminate, but the results are undefined.
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Field Summary
Modifier and TypeFieldDescriptionint
marginBottom specifies the number of points of vertical margin that will be placed along the bottom edge of the layout.int
marginHeight specifies the number of points of vertical margin that will be placed along the top and bottom edges of the layout.int
marginLeft specifies the number of points of horizontal margin that will be placed along the left edge of the layout.int
marginRight specifies the number of points of horizontal margin that will be placed along the right edge of the layout.int
marginTop specifies the number of points of vertical margin that will be placed along the top edge of the layout.int
marginWidth specifies the number of points of horizontal margin that will be placed along the left and right edges of the layout.int
spacing specifies the number of points between the edge of one control and the edge of its neighbouring control. -
Constructor Summary
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Method Summary
Modifier and TypeMethodDescriptionprotected Point
computeSize
(Composite composite, int wHint, int hHint, boolean flushCache) Computes and returns the size of the specified composite's client area according to this layout.protected boolean
flushCache
(Control control) Instruct the layout to flush any cached values associated with the control specified in the argumentcontrol
.protected void
Lays out the children of the specified composite according to this layout.toString()
Returns a string containing a concise, human-readable description of the receiver.
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Field Details
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marginWidth
public int marginWidthmarginWidth specifies the number of points of horizontal margin that will be placed along the left and right edges of the layout. The default value is 0. -
marginHeight
public int marginHeightmarginHeight specifies the number of points of vertical margin that will be placed along the top and bottom edges of the layout. The default value is 0. -
marginLeft
public int marginLeftmarginLeft specifies the number of points of horizontal margin that will be placed along the left edge of the layout. The default value is 0.- Since:
- 3.1
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marginTop
public int marginTopmarginTop specifies the number of points of vertical margin that will be placed along the top edge of the layout. The default value is 0.- Since:
- 3.1
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marginRight
public int marginRightmarginRight specifies the number of points of horizontal margin that will be placed along the right edge of the layout. The default value is 0.- Since:
- 3.1
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marginBottom
public int marginBottommarginBottom specifies the number of points of vertical margin that will be placed along the bottom edge of the layout. The default value is 0.- Since:
- 3.1
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spacing
public int spacingspacing specifies the number of points between the edge of one control and the edge of its neighbouring control. The default value is 0.- Since:
- 3.0
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Constructor Details
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FormLayout
public FormLayout()Constructs a new instance of this class.
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Method Details
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computeSize
Description copied from class:Layout
Computes and returns the size of the specified composite's client area according to this layout.This method computes the size that the client area of the composite must be in order to position all children at their preferred size inside the composite according to the layout algorithm encoded by this layout.
When a width or height hint is supplied, it is used to constrain the result. For example, if a width hint is provided that is less than the width of the client area, the layout may choose to wrap and increase height, clip, overlap, or otherwise constrain the children.
- Specified by:
computeSize
in classLayout
- Parameters:
composite
- a composite widget using this layoutwHint
- width (SWT.DEFAULT
for preferred size)hHint
- height (SWT.DEFAULT
for preferred size)flushCache
-true
means flush cached layout values- Returns:
- a point containing the computed size (width, height)
- See Also:
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Layout.layout(org.eclipse.swt.widgets.Composite, boolean)
Control.getBorderWidth()
Control.getBounds()
Control.getSize()
Control.pack(boolean)
- "computeTrim, getClientArea for controls that implement them"
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flushCache
Description copied from class:Layout
Instruct the layout to flush any cached values associated with the control specified in the argumentcontrol
.- Overrides:
flushCache
in classLayout
- Parameters:
control
- a control managed by this layout- Returns:
- true if the Layout has flushed all cached information associated with control
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layout
Description copied from class:Layout
Lays out the children of the specified composite according to this layout.This method positions and sizes the children of a composite using the layout algorithm encoded by this layout. Children of the composite are positioned in the client area of the composite. The position of the composite is not altered by this method.
When the flush cache hint is true, the layout is instructed to flush any cached values associated with the children. Typically, a layout will cache the preferred sizes of the children to avoid the expense of computing these values each time the widget is laid out.
When layout is triggered explicitly by the programmer the flush cache hint is true. When layout is triggered by a resize, either caused by the programmer or by the user, the hint is false.
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toString
Returns a string containing a concise, human-readable description of the receiver.
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