ComboBox does not accept null value on enter key

Code:

---

@Override
    public Widget asWidget() {


        VerticalLayoutContainer c = new VerticalLayoutContainer();


        List<String> choice = Arrays.asList(null, "1", "2", "3");


        ListStore<String> choiceStore = new ListStore<String>(new ModelKeyProvider<String>() {


            @Override
            public String getKey(String pItem) {
                return pItem;
            }
        });


        choiceStore.addAll(choice);
       
        ComboBox<String> cb = new ComboBox<String>(choiceStore, new LabelProvider<String>() {


            @Override
            public String getLabel(String pItem) {
                return pItem;
            }
        });
       
        c.add(cb);


        return c;
    }

---

Expected:
When I navigate the ComboBox dropdown list with the arrow keys and press enter while the desired value is highlighted, the ComboBox should collapse and display the selected value.

Actual:
Selection works well for the values 1, 2 and 3. Selecting the null value by pressing the enter key does not work. The ComboBox does not collapse.

I moved this thread to the proper forum so we can take a look. Thanks for reporting.

Hi sven,

anything new on this one?

Thanks,
-hcr-

Hi there, any chance of getting that fixed any time soon?

Thanks and best regards,
-hcr-

I've spent a little time working on this, and have a few points to share:

The first issue here is that the example isn't valid - no item is allowed to have a null key. From the ModelKeyProvider javadocs:

Code:

---

  /**
  * Gets a non-null key value that maps to this object. Keys must be consistent and
  * unique for a given model, as a database primary key would be used.
  */
  String getKey(T item);

---

The second again has to do with the value 'null' - what does it mean to select nothing? The ComboBox has a ListView that it uses to draw the dropdown, and when the enter key is hit, the ComboBox asks if anything was selected - it asks if the selected item isn't null. I'm changing this check to see if the list of selected items is _empty_ instead, and then finding the location of the null item.

And one last thought: You can make the item draw full height in the combobox by telling the ComboBox in yet another way that the value null is okay. ComboBox internally uses a SimpleSafeHtmlCell<String> to render, which deliberately skips over null items. This can be replaced by taking over the ListView creation, and making your own cell that draws a null object as a &nbsp;. Here's my finished example, dealing with the first and third issues, and which I am using to find a good workaround for the second:

Code:

---

  public Widget asWidget() {


    VerticalLayoutContainer c = new VerticalLayoutContainer();


    List<String> choice = Arrays.asList(null, "1", "2", "3");


    ListStore<String> choiceStore = new ListStore<String>(new ModelKeyProvider<String>() {


      @Override
      public String getKey(String pItem) {
        return pItem + "";
      }
    });


    choiceStore.addAll(choice);

    ListView<String, String> listView = new ListView<String, String>(choiceStore, new IdentityValueProvider<String>(), new AbstractCell<String>() {
      @Override
      public void render(Cell.Context context, String value, SafeHtmlBuilder sb) {
        if (value == null) {
          sb.appendHtmlConstant("&nbsp;");
        } else {
          sb.appendEscaped(value);
        }
      }
    });
    ComboBox<String> cb = new ComboBox<String>(choiceStore, new LabelProvider<String>() {
      @Override
      public String getLabel(String pItem) {
        return pItem;
      }
    }, listView);

    c.add(cb);


    return c;
  }

---

We've made a fix for this, which is now available in SVN and nightly builds, and will be in the next release. The fix was very nearly as described in my last post - check for an empty set of selected items, rather than asking if the current selected object is null.