Question

How do I read values ​​from the formAttachment in Java?

here is my code:

Text one = new Text(composite, SWT.BORDER);
data = new FormData();
data.top = new FormAttachment(0, 0);
data.bottom = new FormAttachment(100, 0);
data.left = new FormAttachment(0, 0);
data.right = new FormAttachment(sash, 0);
one.setLayoutData(data);

result:

Answer 1

FormAttachments are used to position a Control. You can fix the edges of a control by using the FormAttachment for left, top, right or bottom. All remaining edges are calculated automatically.
The simplest possibility is the percentage positioning relative to the edges of the surrounding composite. Here is an example:

FormData formData = new FormData();
// Fix the left edge of the control to 25% of the overall width + 10px offset.
formData.left = new FormAttachment(25, 10);
// Fix the lower edge of the control to 75% of the overall height + 0px offset.
formData.bottom = new FormAttachment(75);
// Tell the control its new position.
control.setLayoutData(formData);

Alternativelyyou can use the contructor new FormAttachment(control, offset, alignment) to fix an edge of a control relativ to an edge of another control:

FormData formData = new FormData();
// Fix left edge 10px to the right of the right edge of otherControl
formData.left = new FormAttachment(otherControl, 10, SWT.RIGHT);
// Fix bottom edge at exactly the same height as the one of otherControl
formData.bottom = new FormAttachment(otherControl, 0, SWT.BOTTOM);
control.setLayoutData(formData);

There is a really good Eclipse RCP manual by Ralf Ebert here. Unfortunately it is in German. However, you can find images explaining my examples above on the pages 56-57.