Get Active Shell in SWT, even if the Shell is not on focus

Question

Display.getActiveShell() seems to only consider a Shell as active if it's focused. If at the moment another application has focus that means Display.getActiveShell() returns null.

I need a method that will always tell me which is the Shell on focus on my SWT application, even when my SWT application is not on focus.

I've quickly hacked this piece of code together, although sometimes I get an AssertionException:

public static Shell getActiveShell() {
    Display display = Display.getDefault();
    Shell result = display.getActiveShell();

    if (result == null) {
        Shell[] shells = display.getShells();
        for (Shell shell : shells) {
            if (shell.getShells().length == 0) {
                if (result != null)
                    throw new AssertionException();
                result = shell;
            }
        }
    }

    return result;
}

Is there any standard way to approach this issue other than writing your own method?

Recuperator

"I need a method that will always tell me which is the Shell on focus on my SWT application, even when my SWT application is not on focus." the second part is contradicting the first. Can you clarify? – Herat

One thing is to have a shell on focus on my application's context, another thing is to have my swt application on focus! – Recuperator

There is no focus within your application if the application itself does not have the focus. – Herat

There must be some shell that is at least on top of the others? the canonical case being when you have a shell(or dialog or wtv) that doesn't allow you to click in any other shell in the application until its gone. – Recuperator

Answer 1

Recently, I had a similar problem and though you probably found a solution in the meanwhile, I'd like to share mine for future reference.

The ShellActivationTracker adds a display filter that listens for Activate events and - if the activated widget is a Shell - remembers the most recently activated Shell. Thus you can query the (last) active shell even if your application is currently not active/focused.

class ShellActivationTracker implements Listener {
  Shell activeShell;

  ShellActivationTracker(Display display) {
    activeShell = display.getActiveShell();
    display.addFilter(SWT.Activate, this);
  }

  @Override
  public void handleEvent(Event event) {
    if (event.widget instanceof Shell) {
      activeShell = (Shell)event.widget;
    }
  }
}

Richia