Time for action – preserving application state

Follow these steps to see how easy it is to preserve the state of UI components in Vaadin applications:

1. Create a new Vaadin project. We are using keepstate as project name.

2. Code your UI class:

   public class KeepstateUI extends UI {
   
     protected void init(VaadinRequest request) {
       final VerticalLayout layout = new VerticalLayout();
       layout.setMargin(true);
       setContent(layout);
       TextField tf = new TextField(
           "Type, press ENTER, and refresh the browser");
       tf.setImmediate(true);
   
       tf.addValueChangeListener(new ValueChangeListener() {
         public void valueChange(ValueChangeEvent event) {
           Notification.show(
               "Value: " + event.getProperty().getValue());
         }
       });
   
       layout.addComponent(tf);
     }
   
   }

3. Nothing new so far. Run the application, type some text in the text field, and press Enter. You will see something like this:

   

4. Now, refresh the browser and watch out how some text is gone:

   

5. What we want is to...