[news.eclipse.platform.swt] Re: Layouts, minimal height and grabExcessXX

[Eric Rizzo <eclipse-news@xxxxxxxxxxxx>]

Christophe Fondacci wrote:
> Hello all,
>
> I have a little problem with SWT.
> Here it is :
> - I created 2 tables vertically inside a grid composite, separated by a 
> button. The idea is to select an item from the top table and to use the 
> buttons to transfer this item to the bottom table.
> - I would like those 2 tables to grab excess vertical space, and the 
> buttons to always keep the minimal required height (which is the default)
> - Therefore I set the grabExcessVerticalSpace to true for my 2 tables 
> control
> - I do not know the content of those tables at compile time, it depends 
> on what i am editing...
>
> The problem is that when, for example, my first table (the one on top) 
> contains 100 items and the second table is empty, the topmost table 
> takes the entire vertical space and the bottom table is nearly not visible.
>
> I would like those 2 tables to have the same height and to grab the 
> excess height space. I haven't found any way to do this.

This is a general problem people run into when using GridLayout with 
widgets that like their "preferred" size to be as big as their contents. 
The GridLayout algorithm wants to respect the preferred size of its 
children, which in the case of a table is as tall as necessary to 
display all the rows without scrolling. So the GridLayout is respecting 
that and giving your one table all the space it "asks" for.
A trick when using GridLayout to keep a widget from taking too much 
space is to force its "preferred" size to be tiny and then specify that 
it grab excess space and fill its alignment. You can use the heightHint 
property of the GridData to do that - just set it to 1 and the widget's 
"preferred" size will be 1 pixel. If the same widget's GridData also 
specifies that it be greedy (FILL alignment and grabExcess=true), then 
it will expand to fill the space its parent layout give it. This 
combination usually genertes the behavior you want, which is that the 
widget (Table in your case) expands to fill available space but does not 
ask for more than its fair share.
Below is a snippet that should work for you. Note that this stays with 
the GridLayout; I do like, however, the other recommendation to use 
FormLayout which is a lot more flexible but also more complex, 
especially if you're coding it by hand without the benefit of a WYSIWYG 
tool.
By the way, the snippet below was generated using the very-handy "SWT 
Layout Example" tool available here: http://www.eclipse.org/swt/examples.php


--- Begin included file ---
import org.eclipse.swt.SWT;
import org.eclipse.swt.layout.GridData;
import org.eclipse.swt.layout.GridLayout;
import org.eclipse.swt.widgets.Button;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Shell;
import org.eclipse.swt.widgets.Table;
import org.eclipse.swt.widgets.TableItem;

public class MyLayout {
public static void main (String [] args) {
	Display display = new Display ();
	Shell shell = new Shell (display);
	GridLayout gridLayout = new GridLayout ();
	shell.setLayout (gridLayout);

	Table table0 = new Table (shell, SWT.BORDER);
	table0.setLinesVisible (true);
	for (int i = 0; i < 20; i++) {
		new TableItem (table0, SWT.NONE).setText("Item " + i);
	}

	GridData data = new GridData ();
	data.horizontalAlignment = GridData.FILL;
	data.verticalAlignment = GridData.FILL;
	data.grabExcessHorizontalSpace = true;
	data.grabExcessVerticalSpace = true;
	data.heightHint = 1;
	table0.setLayoutData (data);

	Button button1 = new Button (shell, SWT.PUSH);
	button1.setText ("button1");
	data = new GridData ();
	data.horizontalAlignment = GridData.CENTER;
	button1.setLayoutData (data);

	Table table2 = new Table (shell, SWT.BORDER);
	table2.setLinesVisible (true);
	TableItem tableItem21 = new TableItem (table2, SWT.NONE);
	tableItem21.setText ("Item1");
	TableItem tableItem22 = new TableItem (table2, SWT.NONE);
	tableItem22.setText ("Item2");
	data = new GridData ();
	data.horizontalAlignment = GridData.FILL;
	data.verticalAlignment = GridData.FILL;
	data.grabExcessHorizontalSpace = true;
	data.grabExcessVerticalSpace = true;
	table2.setLayoutData (data);

	//shell.pack ();
	shell.setSize(500, 500);
	shell.open ();

	while (!shell.isDisposed ()) {
		if (!display.readAndDispatch ())
			display.sleep ();
	}
	display.dispose ();
}
}