Table generated buttons

Before diving in the middle of the subject, let’s have a use-case first. Imagine we have a CRUD application and our current screen lists the datastore entities in a table, a line per entity and a column per property.

Now, in order to implement the Delete functionality, we use the addGeneratedColumn method of the Table component to display a “Delete” button, like in the following screenshot:

The problem lies in the action that has to take place when the button is pressed. The behavior needs to be determined when the page is generated, so that the event is processed directly on the server-side: in other words, we need a way to pass the entity identifier (or the container’s item or even the container’s item id) to the button somehow.

The solution is very simple to implement, with just the use of the final keyword, to let nested anonymous class methods access parameters:

table.addGeneratedColumn("", new ColumnGenerator() {
 
  @Override public Object generateCell(final Table source, final Object itemId, Object columnId) {
 
    Button button = new Button("Delete");
 
    button.addListener(new ClickListener() {
 
      @Override public void buttonClick(ClickEvent event) {
 
        source.getContainerDataSource().removeItem(itemId);
      }
    });
 
    return button;
  }
});