Class FormLayout
- java.lang.Object
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- org.eclipse.swt.widgets.Layout
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- org.eclipse.swt.layout.FormLayout
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public final class FormLayout extends Layout
Instances of this class control the position and size of the children of a composite control by usingFormAttachments
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 aShell
: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 aFormData
withFormAttachment
for each child ofComposite
. The following example code attachesbutton1
to the top and left edge of the composite andbutton2
to the right edge ofbutton1
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 ofFormAttachment
and setting them into the top, bottom, left, and right fields of the child'sFormData
.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
andbutton2
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 ofbutton2
and then attach the left edge ofbutton2
to the right edge ofbutton1
. This will over constrain the layout, causing undefined behavior. The algorithm will terminate, but the results are undefined.- Since:
- 1.0
- See Also:
FormData
,FormAttachment
, FormLayout snippets, SWT Example: LayoutExample, Sample code and further information
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Field Summary
Fields Modifier and Type Field Description int
marginBottom
marginBottom specifies the number of pixels of vertical margin that will be placed along the bottom edge of the layout.int
marginHeight
marginHeight specifies the number of pixels of vertical margin that will be placed along the top and bottom edges of the layout.int
marginLeft
marginLeft specifies the number of pixels of horizontal margin that will be placed along the left edge of the layout.int
marginRight
marginRight specifies the number of pixels of horizontal margin that will be placed along the right edge of the layout.int
marginTop
marginTop specifies the number of pixels of vertical margin that will be placed along the top edge of the layout.int
marginWidth
marginWidth specifies the number of pixels of horizontal margin that will be placed along the left and right edges of the layout.int
spacing
spacing specifies the number of pixels between the edge of one control and the edge of its neighbouring control.
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Constructor Summary
Constructors Constructor Description FormLayout()
Constructs a new instance of this class.
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description protected 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
layout(Composite composite, boolean flushCache)
Lays out the children of the specified composite according to this layout.java.lang.String
toString()
Returns a string containing a concise, human-readable description of the receiver.
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Field Detail
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marginWidth
public int marginWidth
marginWidth specifies the number of pixels of horizontal margin that will be placed along the left and right edges of the layout. The default value is 0.
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marginHeight
public int marginHeight
marginHeight specifies the number of pixels of vertical margin that will be placed along the top and bottom edges of the layout. The default value is 0.
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marginLeft
public int marginLeft
marginLeft specifies the number of pixels of horizontal margin that will be placed along the left edge of the layout. The default value is 0.
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marginTop
public int marginTop
marginTop specifies the number of pixels of vertical margin that will be placed along the top edge of the layout. The default value is 0.
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marginRight
public int marginRight
marginRight specifies the number of pixels of horizontal margin that will be placed along the right edge of the layout. The default value is 0.
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marginBottom
public int marginBottom
marginBottom specifies the number of pixels of vertical margin that will be placed along the bottom edge of the layout. The default value is 0.
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spacing
public int spacing
spacing specifies the number of pixels between the edge of one control and the edge of its neighbouring control. The default value is 0.
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Method Detail
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computeSize
protected Point computeSize(Composite composite, int wHint, int hHint, boolean flushCache)
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:
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
protected boolean flushCache(Control control)
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
protected void layout(Composite composite, boolean flushCache)
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
public java.lang.String toString()
Returns a string containing a concise, human-readable description of the receiver.- Overrides:
toString
in classjava.lang.Object
- Returns:
- a string representation of the layout
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