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Eclipse Rich Ajax Platform
Release 1.2

org.eclipse.swt.layout
Class FormLayout

java.lang.Object
  extended by

org.eclipse.swt.widgets.Layout
      extended by
org.eclipse.swt.layout.FormLayout

public final class FormLayout
extends Layout

Instances of this class control the position and size of the children of a composite control by using 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.

Since:
1.0
See Also:
FormData, FormAttachment, FormLayout snippets, SWT Example: LayoutExample, Sample code and further information

Field Summary
 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.
 
Constructor Summary
FormLayout ()
          Constructs a new instance of this class.
 
Method Summary
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 argument control.
protected  void layout ( Composite composite, boolean flushCache)
          Lays out the children of the specified composite according to this layout.
  String toString ()
          Returns a string containing a concise, human-readable description of the receiver.
 
Methods inherited from class java.lang. Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
 

Field Detail

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.


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.


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.


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.


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.


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.


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.

Constructor Detail

FormLayout

public FormLayout()
Constructs a new instance of this class.

Method Detail

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 class Layout
Parameters:
composite - a composite widget using this layout
wHint - 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"

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 argument control.

Overrides:
flushCache in class Layout
Parameters:
control - a control managed by this layout
Returns:
true if the Layout has flushed all cached information associated with control

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.

Specified by:
layout in class Layout
Parameters:
composite - a composite widget using this layout
flushCache - true means flush cached layout values

toString

public 
String toString()
Returns a string containing a concise, human-readable description of the receiver.

Returns:
a string representation of the layout

Eclipse Rich Ajax Platform
Release 1.2

Copyright (c) Innoopract Informationssysteme GmbH and others 2002, 2008. All rights reserved.


 
 
  Published under the terms of the Eclipse Public License Version 1.0 ("EPL") Design by Interspire