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org.eclipse.swt.layout
Class FormLayout
java.lang.Objectorg.eclipse.swt.widgets.Layout
- public final class FormLayout
- extends org.eclipse.swt.widgets.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 edge 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 it's preferred size. If a child
is given no attachments 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:
- 2.0
| Field Summary | |
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 |
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 | |
(package private) int |
computeHeight(FormData data)
Computes the preferred height of the form with respect to the preferred height of the control. |
protected org.eclipse.swt.graphics.Point |
computeSize(org.eclipse.swt.widgets.Composite composite,
int wHint,
int hHint,
boolean flushCache)
Computes and returns the size of the specified composite's client area according to this layout. |
(package private) org.eclipse.swt.graphics.Point |
computeSize(org.eclipse.swt.widgets.Control control,
boolean flushCache)
|
(package private) int |
computeWidth(FormData data)
Computes the preferred height of the form with respect to the preferred height of the control. |
protected void |
layout(org.eclipse.swt.widgets.Composite composite,
boolean flushCache)
Lays out the children of the specified composite according to this layout. |
(package private) org.eclipse.swt.graphics.Point |
layout(org.eclipse.swt.widgets.Composite composite,
boolean move,
int x,
int y,
int width,
int height,
boolean flushCache)
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| Methods inherited from class java.lang.Object |
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, 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.
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.
- Since:
- 3.0
| Constructor Detail |
FormLayout
public FormLayout()
- Constructs a new instance of this class.
| Method Detail |
computeHeight
int computeHeight(FormData data)
- Computes the preferred height of the form with
respect to the preferred height of the control.
Given that the equations for top (T) and bottom (B)
of the control in terms of the height of the form (X)
are:
T = AX + B
B = CX + D
The equation for the height of the control (H)
is bottom (B) minus top (T) or (H = B - T) or:
H = (CX + D) - (AX + B)
Solving for (X), the height of the form, we get:
X = (H + B - D) / (C - A)
When (A = C), (C - A = 0) and the equation has no
solution for X. This is a special case meaning that
the control does not constrain the height of the
form. In this case, we need to arbitrarily define
the height of the form (X):
Case 1: A = C, A = 0, C = 0
Let X = D, the distance from the top of the form
to the bottom edge of the control. In this case,
the control was attatched to the top of the form
and the form needs to be large enough to show the
bottom edge of the control.
Case 2: A = C, A = 1, C = 1
Let X = -B, the distance from the bottom of the
form to the top edge of the control. In this case,
the control was attached to the bottom of the form
and the only way that the control would be visible
is if the offset is negative. If the offset is
positive, there is no possible height for the form
that will show the control as it will always be
below the bottom edge of the form.
Case 3: A = C, A != 0, C != 0 and A != 1, C != 0
Let X = D / (1 - C), the distance from the top of the
form to the bottom edge of the control. In this case,
since C is not 0 or 1, it must be a fraction, U / V.
The offset D is the distance from CX to the bottom edge
of the control. This represents a fraction of the form
(1 - C)X. Since the height of a fraction of the form is
known, the height of the entire form can be found by setting
(1 - C)X = D. We solve this equation for X in terms of U
and V, giving us X = (U * D) / (U - V). Similarily, if the
offset D is negative, the control is positioned above CX.
The offset -B is the distance from the top edge of the control
to CX. We can find the height of the entire form by setting
CX = -B. Solving in terms of U and V gives us X = (-B * V) / U.
computeSize
protected org.eclipse.swt.graphics.Point computeSize(org.eclipse.swt.widgets.Composite composite, int wHint, int hHint, boolean flushCache)
- Description copied from class:
org.eclipse.swt.widgets.Layout - Computes and returns the size of the specified
composite's client area according to this layout.
This method computes the minimum size that the client area of the composite must be in order to position all children at their minimum 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 minimum width of the client area, the layout may choose to wrap and increase height, clip, overlap, or otherwise constrain the children.
computeSize
org.eclipse.swt.graphics.Point computeSize(org.eclipse.swt.widgets.Control control, boolean flushCache)
computeWidth
int computeWidth(FormData data)
- Computes the preferred height of the form with
respect to the preferred height of the control.
layout
protected void layout(org.eclipse.swt.widgets.Composite composite, boolean flushCache)
- Description copied from class:
org.eclipse.swt.widgets.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 layed 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.
layout
org.eclipse.swt.graphics.Point layout(org.eclipse.swt.widgets.Composite composite, boolean move, int x, int y, int width, int height, boolean flushCache)
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DETAIL: FIELD | CONSTR | METHOD | ||||||||