still is: out of sync, can you help me confirm some questions?

Now, I do some operation in two browser, the popup error messages: out of sync,

I have following codes:

protected void onDetach() {

but not config GAEApplicationServlet in web.xml,

  1. must config this servelt ?
  2. or somewhere in codes not righ ?

What job must do to avoid the error: out of sync ?


Do you update some UI elements on server side ?

Sounds like you are trying to update UI from another thread.
For this to work you need to synchronise correctly.

public void makeSomeUpdates() {
    for (int i = 0; i<100; ++i) {
        synchronized(textField.getApplication()) {
            textField.setValue("Now i equals "+i);
            checkBox.setValue(i % 2 == 0);
        // do some background processing here, not touching Vaadin UI components nor
        // the data structures they are accessing

yes, I am trying to update UI from another thread. or from other computer/client
debug the codes, found always get same application instance from different client,

I know my requirement now, I posted a new thread: