org.eclipse.swt.layout.FormLayout Maven / Gradle / Ivy
/*******************************************************************************
* Copyright (c) 2000, 2008 IBM Corporation and others.
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/legal/epl-v10.html
*
* Contributors:
* IBM Corporation - initial API and implementation
*******************************************************************************/
package org.eclipse.swt.layout;
import org.eclipse.swt.SWT;
import org.eclipse.swt.graphics.Point;
import org.eclipse.swt.graphics.Rectangle;
import org.eclipse.swt.widgets.Composite;
import org.eclipse.swt.widgets.Control;
import org.eclipse.swt.widgets.Layout;
import org.eclipse.swt.widgets.Scrollable;
/**
* 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.
*
*
* @see FormData
* @see FormAttachment
* @see FormLayout snippets
* @see SWT Example: LayoutExample
* @see Sample code and further information
*
* @since 1.0
*/
public final class FormLayout extends Layout {
/**
* 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.
*/
public int marginWidth = 0;
/**
* 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.
*/
public int marginHeight = 0;
/**
* 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.
*/
public int marginLeft = 0;
/**
* 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.
*/
public int marginTop = 0;
/**
* 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.
*/
public int marginRight = 0;
/**
* 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.
*/
public int marginBottom = 0;
/**
* spacing specifies the number of pixels between the edge of one control
* and the edge of its neighbouring control.
*
* The default value is 0.
*/
public int spacing = 0;
/**
* Constructs a new instance of this class.
*/
public FormLayout () {
}
/*
* 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 attached 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). Similarly, 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.
*/
int computeHeight (Control control, FormData data, boolean flushCache) {
FormAttachment top = data.getTopAttachment (control, spacing, flushCache);
FormAttachment bottom = data.getBottomAttachment (control, spacing, flushCache);
FormAttachment height = bottom.minus (top);
if (height.numerator == 0) {
if (bottom.numerator == 0) return bottom.offset;
if (bottom.numerator == bottom.denominator) return -top.offset;
if (bottom.offset <= 0) {
return -top.offset * top.denominator / bottom.numerator;
}
int divider = bottom.denominator - bottom.numerator;
return bottom.denominator * bottom.offset / divider;
}
return height.solveY (data.getHeight (control, flushCache));
}
protected Point computeSize (Composite composite, int wHint, int hHint, boolean flushCache) {
Point size = layout (composite, false, 0, 0, wHint, hHint, flushCache);
if (wHint != SWT.DEFAULT) size.x = wHint;
if (hHint != SWT.DEFAULT) size.y = hHint;
return size;
}
protected boolean flushCache (Control control) {
Object data = control.getLayoutData ();
if (data != null) ((FormData) data).flushCache ();
return true;
}
String getName () {
String string = getClass ().getName ();
int index = string.lastIndexOf ('.');
if (index == -1) return string;
return string.substring (index + 1, string.length ());
}
/*
* Computes the preferred height of the form with
* respect to the preferred height of the control.
*/
int computeWidth (Control control, FormData data, boolean flushCache) {
FormAttachment left = data.getLeftAttachment (control, spacing, flushCache);
FormAttachment right = data.getRightAttachment (control, spacing, flushCache);
FormAttachment width = right.minus (left);
if (width.numerator == 0) {
if (right.numerator == 0) return right.offset;
if (right.numerator == right.denominator) return -left.offset;
if (right.offset <= 0) {
return -left.offset * left.denominator / left.numerator;
}
int divider = right.denominator - right.numerator;
return right.denominator * right.offset / divider;
}
return width.solveY (data.getWidth (control, flushCache));
}
protected void layout (Composite composite, boolean flushCache) {
Rectangle rect = composite.getClientArea ();
int x = rect.x + marginLeft + marginWidth;
int y = rect.y + marginTop + marginHeight;
int width = Math.max (0, rect.width - marginLeft - 2 * marginWidth - marginRight);
int height = Math.max (0, rect.height - marginTop - 2 * marginHeight - marginBottom);
layout (composite, true, x, y, width, height, flushCache);
}
Point layout (Composite composite, boolean move, int x, int y, int width, int height, boolean flushCache) {
Control [] children = composite.getChildren ();
for (int i=0; i