[news.eclipse.platform.swt] Re: Canvas vs Composite Question....

[Eric Rizzo <eclipse-news@xxxxxxxxxxxx>]

Emil Crumhorn wrote:
> You're on the right track but I think you need a push in the right 
> direction. I've taken your code and created a test example that you can run. 
> Compare it with your code to see some differences. Note the use of the 
> layouts even on the widget you're drawing on to. Otherwise you'd never see 
> the native widgets, just what you draw. Also note that you have to take into 
> account how you're drawing a background when you put widgets on top, some 
> layouts may simply position sub-composites on top of what you're drawing and 
> you'd never see it (and sometimes you will probably want to write your own 
> Layout class that deals with all that for you).
> Code (copy & paste into Eclipe and run the code formatter, CTRL+SHIFT+F)
> ---

The code had shell.open() commented out, so it never showed the window.
Try this slightly modified example, which also demonstrates a more 
real-world layout and corrects the Canvas layout's margin.

import org.eclipse.swt.SWT;
import org.eclipse.swt.events.PaintEvent;
import org.eclipse.swt.events.PaintListener;
import org.eclipse.swt.graphics.GC;
import org.eclipse.swt.graphics.Rectangle;
import org.eclipse.swt.layout.FillLayout;
import org.eclipse.swt.layout.GridData;
import org.eclipse.swt.layout.GridLayout;
import org.eclipse.swt.widgets.Canvas;
import org.eclipse.swt.widgets.Composite;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Label;
import org.eclipse.swt.widgets.Shell;
import org.eclipse.swt.widgets.Text;

public class CustomDrawCompositeDemo {

	public static void main(String[] args) {
		// standard display and shell etc
		Display display = new Display();
		Shell shell = new Shell(display);
		shell.setText("Shell");
		shell.setSize(200, 200);
		shell.setLayout(new FillLayout());

		// create your widget as it's the outer-most widget, it's a child of 
the shell
		MyWidget mw = new MyWidget(shell, SWT.NONE);

		// this layout will lay out widgets inside the canvas where you are
		// drawing the border
		GridLayout gl = new GridLayout();
		gl.marginHeight = 10;
		gl.marginWidth = 10;
		mw.setLayout(gl);

		// create the composite that holds your widgets (labels etc) and put it
		// on the MyWidget
		Composite inner = new InnerComposite(mw, SWT.NONE);
		inner.setLayoutData(new GridData(GridData.FILL_BOTH));

		shell.open();
		while (!shell.isDisposed()) {
			if (!display.readAndDispatch())
				display.sleep();
		}
		display.dispose();
	}
	// this class only deals with native components
	static class InnerComposite extends Composite {

		public InnerComposite(Composite parent, int style) {
			super(parent, style);

			setLayout(new GridLayout(2, false));

			Label one = new Label(this, SWT.None);
			one.setText("One:");
			Text text1 = new Text(this, SWT.BORDER);
			text1.setLayoutData(new GridData(GridData.FILL_HORIZONTAL));
			Label two = new Label(this, SWT.None);
			two.setText("Two:");
			Text text2 = new Text(this, SWT.BORDER);
			text2.setLayoutData(new GridData(GridData.FILL_HORIZONTAL));
		}
	}

	// this class only deals with drawing
	static class MyWidget extends Canvas {

		public MyWidget(Composite parent, int style) {
			super(parent, style);

			addPaintListener(new PaintListener() {
				public void paintControl(PaintEvent e) {
					drawControl(e);
				}
			});
		}

		// draws the border
		public void drawControl(PaintEvent e) {
			GC gc = e.gc;
			Rectangle rect = getClientArea();
			gc.setLineWidth(2);
			gc.setLineStyle(SWT.LINE_DASH);

			// draw it a little inside of the total space that we take up
			gc.drawRectangle(rect.x + 5, rect.y + 5, rect.width - 10, rect.height 
- 10);
		}

	}

}