JAVA - how to modify SWT UI while looping in thread

I'm trying to implement a Desktop app that loops trough a function and sets a textfield on the UI every 1 sec.

But I either get

org.eclipse.swt.SWTException: Invalid thread access


when I don't use the display

or the UI is really sluggish when I do

display.asyncExec(new Runnable() {


My code looks like this:

public void open() {
Display display = Display.getDefault();
shell = new Shell();
shell.setSize(486, 322);
shell.setText("SWT Application");

Button btnStartLoop = new Button(shell, SWT.NONE);
btnStartLoop.addMouseListener(new MouseAdapter() {
@Override
public void mouseDown(MouseEvent e) {
SwingUtilities.invokeLater(new Runnable() {
public void run() // updates displayArea
{
while (true) {
try {
text.setText("Text has been set");
Thread.sleep(1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
});
}
});
btnStartLoop.setBounds(35, 30, 75, 25);
btnStartLoop.setText("Start Loop");

text = new Text(shell, SWT.BORDER);
text.setText("0");
text.setBounds(116, 32, 177, 21);
shell.open();
shell.layout();
while (!shell.isDisposed()) {
if (!display.readAndDispatch()) {
display.sleep();
}
}
}


is there any way this can be overcome?

1 Answer
1

You must never sleep in the UI thread. You must use a new Thread for the background activity. You call Display.asyncExec from within the thread to run the UI update code in the UI thread.

Thread

Display.asyncExec

btnStartLoop.addMouseListener(new MouseAdapter() {
@Override
public void mouseDown(final MouseEvent e) {
final Thread background = new Thread(new Runnable() {
public void run()
{
while (true) {
try {
Display.getDefault().asyncExec(() -> text.setText("Text has been set"));
Thread.sleep(1000);
} catch (final InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
});
background.start();
}
});


Note: SwingUtilities is for Swing applications, do not use it in SWT apps.

SwingUtilities

You can also use the timerExec method of Display to run code after a specific delay which avoids the need for a background thread.

timerExec

Display

btnStartLoop.addMouseListener(new MouseAdapter() {
@Override
public void mouseDown(final MouseEvent e) {
final Runnable update = new Runnable() {
public void run()
{
text.setText("Text has been set");

Display.getDefault().timerExec(1000, this);
}
};
Display.getDefault().timerExec(0, update);
}
});


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