Binder.discard is not discarding all components. what happens on binder.dis

Flow
1

Hi All,

I am new to vaading and trying to understand and learn. I am working on a binder and trying to understand what happens
when we call discard method.

In my scenario, I am binding the fields through binder.bind(persontxt,“person”), I have all the form fields bounded and when i do discard only
few fields are getting discarded. I want to know how this happens and how shall I not discard particular fields?

Kindly help to understand this.

Thanks,
Prajna

2

Hi,

which Vaadin version are you using? I don’t see a discard method in Binder of Vaadin 14.1: https://vaadin.com/api/platform/14.1.23/com/vaadin/flow/data/binder/Binder.html so I’m not sure what you’re talking about.

Additionally, are you able to create a small code example that demonstrates what is going on?

-Olli

3

Hi Olli,
I am using vaadin 7, here is a sample code.when i click on discard I am expecting it to clearing the text fields.
Which is not happening. I want to understand what happens when a discard method called.

public class BinderView extends FormLayout implements View {

	private static final long serialVersionUID = -4490987023164596949L;

	public BinderView() {
		// Have some layout and create the fields
		FormLayout form = new FormLayout();

		TextField nameField = new TextField("Name");
		form.addComponent(nameField);

		TextField ageField = new TextField("Age");
		form.addComponent(ageField);
		
		// Now create the binder and bind the fields
		//Bean is a java pojo class containing a string and double variable
		Bean myBeanClass = new Bean("prajna",29.11);
		BeanItem<Bean> item = new BeanItem<>(myBeanClass);
		FieldGroup binder = new FieldGroup(item);
		binder.setBuffered(true);
		binder.bind(nameField, "name");
		binder.bind(ageField, "energy");
		
		Button refreshBtn = new Button("Refresh", new Button.ClickListener() {

			private static final long serialVersionUID = 2251260916396644988L;

			@Override
			public void buttonClick(ClickEvent event) {
				//clear the text fields
				binder.discard();
			}
		});
		form.addComponent(refreshBtn);
		addComponent(form);
	}

	@Override
	public void enter(ViewChangeEvent event) {
	}
}

Thanks,
Prajna

4

Okay, you’re talking about FieldGroup? binder is just the name of a variable in your own code. What FieldGroup.discard does is call discard on every Field connected to it. The behavior from the Field’s discard method can be seen from its JavaDoc:

 /**
     * Discards all changes since last commit. The object updates its value from
     * the data source.
     *
     * @throws SourceException
     *             if the operation fails because of an exception is thrown by
     *             the data source. The cause is included in the exception.
     */
    public void discard() throws SourceException;

So discarding doesn’t clear a TextField, it reverts any Field back to the value it has in the data source (in your case, the Bean myBeanClass).

PS. Vaadin 7 has not been publicly maintained for a few years now; you should look into migrating to a newer version.

5

Okay, thanks!
so if I need to clear the text field, for a refresh functionality I need to explicitly make the field null correct ?
-Prajna

6

Null or empty, yes.