PopupScreen not show after pushing

I push the pop screen using following code, what pop screen not displays. Please tell me what I missed.?

LabelField statusMsg =  new LabelField("Hello");
PopupScreen statusScree开发者_JAVA技巧n = new PopupScreen((fieldHFM));
UiApplication app = UiApplication.getUiApplication();
app.pushScreen(statusScreen);

Try to do in following way

UiApplication.getUiApplication().invokeLater(new Runnable() {
                    public void run() {
                        UiApplication.getUiApplication().pushScreen(statusScreen);
                    }
                });