SWT update UI from another thread

SWT is a single-threaded UI toolkit and therefore when is needed to update the UI from a different thread the asyncExec method from Display class is needed to be used. To update the UI from another thread is really common for long operations to avoid the application being unresponsive.

Display.getDefault().asyncExec(new Runnable() {
    public void run() {
        /** UI update code */
    }
});

Example

Here is a full example how to update the SWT UI from another thread.

package com.admfactory.swt;

import org.eclipse.swt.SWT;
import org.eclipse.swt.layout.GridLayout;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Label;
import org.eclipse.swt.widgets.Shell;

public class UIUpdateThreadSWT {
    
    private static int counter = 0;

    public static void main(String[] args) throws Exception {
	final Display display = new Display();
	/** create the new window */
	Shell shell = new Shell(display);

	/** adding the window title */
	shell.setText("Update UI from thread examples");

	/** add a layout of 1 columns */
	shell.setLayout(new GridLayout(1, true));
	
	/** setting up the window size */
	shell.setSize(600, 400);
	
	/** creating a new label widget on the new created shell */
	final Label label = new Label(shell, SWT.NONE);
	label.setText(counter + "");

	/** open the shell/window */
	shell.open();

	Thread thread = new Thread(new Runnable() {

	    @Override
	    public void run() {
		while (true) {
		    display.asyncExec(new Runnable() {
			public void run() {
			    /**
			     * this is in case that the thread starts before the
			     * UI is created
			     */
			    if (label == null || label.isDisposed())
				return;
			    label.setText("" + counter);
			}
		    });
		    counter++;
		    try {
			Thread.sleep(1000);
		    } catch (InterruptedException e) {
			e.printStackTrace();
		    }
		}
	    }
	});

	/** start the working thread */
	thread.start();

	/** Loop to keep the application opened */
	while (!shell.isDisposed()) {
	    if (!display.readAndDispatch()) {
		display.sleep();
	    }
	}
	display.dispose();
    }
}

Output

You can notice the label being updated every 1 sec.

References

• SWT Homepage