Updating SWT periodically causes GUI to freeze

Question

Problem: SWT freezes when GUI field is periodically updated.

I would like to have a SWT-based GUI with text field were values are periodically increment

Answer 1

Any SWT operation which changes a UI object must be run on the SWT User Interface thread.

In your case the text.setText(i.toString()); line is an SWT UI operation and is running in a different thread.

You can use the asyncExec or syncExec methods of Display to run some code in the UI thread. So replace:

text.setText(i.toString());

with

final String newText = i.toString();
Display.getDefault().asyncExec(() -> text.setText(newText));

(this is assuming you are using Java 8).

Using asyncExec will do the UI update asynchronously. Use syncExec instead if you want to pause the thread until the update is done.

If you are using Java 7 or earlier use:

 final String newText = i.toString();
 Display.getDefault().asyncExec(new Runnable() {
    @Override
    public void run() {
      text.setText(newText);
    }
 });

Note you should also be checking for the Shell being disposed and stopping your background thread. If you don't do this you will get an error when you close the app. Your code incrementing i is also wrong. This thread works:

new Thread(() -> {
    for (int i = 1; true; i++) {
        try {
            Thread.sleep(1000);
        } catch (final InterruptedException e) {
            return;
        }

        if (shell.isDisposed())  // Stop thread when shell is closed
          break;

        final String newText = Integer.toString(i);
        Display.getDefault().asyncExec(() -> text.setText(newText));
    }
}).start();