Issue with AsyncCallback. Value is returning before onSuccess method gets executed

Question

I have written the following code. This piece of code just basically retrieving the value from the database. But the issue is happening that it is returning the value before completion of the onSuccess method.

How to mitigate the problem?

private static final SomeServiceAsync service = GWT.create(SomeService.class);

private static boolean valueIndicator = true;

private static boolean checkValueOfVariable() {
    service.isValueTurnedOn(new AsyncCallback<Boolean>() {
        @Override
        public void onFailure(Throwable caught) {
            Window.alert("Failed to retrieve value."+caught.getLocalizedMessage());
        }

        @Override
        public void onSuccess(Boolean value) {
            valueIndicator = value;
        }
    });
    return valueIndicator;
}

I want to return the value after execution of onSuccess method.

You might benefit from reading https://stackoverflow.com/questions/14220321/how-do-i-return-the-response-from-an-asynchronous-call, quite informative and almost language-independent. — walen, Jul 09 '19 at 09:18

score 1 · Accepted Answer · answered Jul 09 '19 at 07:45

This will not work.

The server call is asynchron. So the method will return the value before the server call has returned.

Use a callback:

public interface ReturnHandler {

  void onReturn(Boolean value);

}

Try:

private static void checkValueOfVariable(ReturnHandler handler) {
    service.isValueTurnedOn(new AsyncCallback<Boolean>() {
        @Override
        public void onFailure(Throwable caught) {
            Window.alert("Failed to retrieve value."+caught.getLocalizedMessage());
        }

        @Override
        public void onSuccess(Boolean value) {
            handler.onReturn(value);
        }
    });
}

and call it using:

checkValueOfVariable(new ReturnHandler() {
  public void onReturn(Boolean value) {
    valueIndicator = value;
  }
)

Hope that helps.

Issue with AsyncCallback. Value is returning before onSuccess method gets executed

1 Answers1