ComboBox setNullSelectionAllowed(true) does not show item in drop down

Vaadin 6 / 7 / 8 Framework UI
1

I am working on a survey that I would like to track the complete percentage of the questions with answers. Everything works when a value is selected, but I want to be able to select a null value to un-select an answer. When I tried to do this without implicitly specifying setNullSelectionAllowed to true, I would get a NullPointerException when comboBox.getValue() was called. This guided me to set the setNullSelectionAllowed to true. After compiling and deploying, the blank value that was there initially is gone, so I cannot select a value for null. Here is the code for the ComboBox:


		final ComboBox resultBox = new ComboBox();
		resultBox.setImmediate(true);
		resultBox.setWidth("100%");
		resultBox.setNullSelectionAllowed(true);
		resultBox.addItem(-1);
		resultBox.setItemCaption(-1, " ");
		resultBox.setNullSelectionItemId(-1);

		if (question.getResponseType() == 2)
		{
			resultBox.addItem(ResponseValue.ONE.ordinal());
			resultBox.setItemCaption(ResponseValue.ONE.ordinal(), ResponseValue.ONE.display());
			resultBox.addItem(ResponseValue.TWO.ordinal());
			resultBox.setItemCaption(ResponseValue.TWO.ordinal(), ResponseValue.TWO.display());
			resultBox.addItem(ResponseValue.THREE.ordinal());
			resultBox.setItemCaption(ResponseValue.THREE.ordinal(), ResponseValue.THREE.display());
			resultBox.addItem(ResponseValue.FOUR.ordinal());
			resultBox.setItemCaption(ResponseValue.FOUR.ordinal(), ResponseValue.FOUR.display());
			resultBox.addItem(ResponseValue.FIVE.ordinal());
			resultBox.setItemCaption(ResponseValue.FIVE.ordinal(), ResponseValue.FIVE.display());
			resultBox.addItem(ResponseValue.SIX.ordinal());
			resultBox.setItemCaption(ResponseValue.SIX.ordinal(), ResponseValue.SIX.display());
			resultBox.addItem(ResponseValue.SEVEN.ordinal());
			resultBox.setItemCaption(ResponseValue.SEVEN.ordinal(), ResponseValue.SEVEN.display());
			resultBox.addItem(ResponseValue.EIGHT.ordinal());
			resultBox.setItemCaption(ResponseValue.EIGHT.ordinal(), ResponseValue.EIGHT.display());
			resultBox.addItem(ResponseValue.NINE.ordinal());
			resultBox.setItemCaption(ResponseValue.NINE.ordinal(), ResponseValue.NINE.display());
			resultBox.addItem(ResponseValue.TEN.ordinal());
			resultBox.setItemCaption(ResponseValue.TEN.ordinal(), ResponseValue.TEN.display());
		} 
		else 
		{
			resultBox.addItem(ResponseValue.PASS.ordinal());
			resultBox.setItemCaption(ResponseValue.PASS.ordinal(), ResponseValue.PASS.display());
			resultBox.addItem(ResponseValue.FAIL.ordinal());
			resultBox.setItemCaption(ResponseValue.FAIL.ordinal(), ResponseValue.FAIL.display());
			resultBox.addItem(ResponseValue.N_A.ordinal());
			resultBox.setItemCaption(ResponseValue.N_A.ordinal(), ResponseValue.N_A.display());
		}
		
		resultBox.addListener(new ComboBox.ValueChangeListener() 
		{
			
			@Override
			public void valueChange(ValueChangeEvent event) 
			{
				Result result = (Result) table.getItem(item).getItemProperty("result").getValue();
				
				if (result == null && !resultBox.isSelected(-1))
				{
					result = Result.create(survey, question);
					table.getItem(item).getItemProperty("result").setValue(result);
				}
				
				else if (result != null && resultBox.isSelected(-1))
				{
					result=Result.create(survey, question);
					table.getItem(item).getItemProperty("result").setValue(null);
				}
				
				result.setResultsValue((Integer) resultBox.getValue());
				getDataSource().updateResult(result);
			}
		});

resultBox.addListener(new Property.ValueChangeListener()
		{
			private static final long serialVersionUID = -6792325980430002436L;

			@Override
			public void valueChange(ValueChangeEvent event)
			{
				if (ignoreUpdates)
				{
					return;
				}
				
				Result result = (Result) table.getItem(item).getItemProperty("result").getValue();
				
				if (result == null)
				{
					result = Result.create(survey, question);
					table.getItem(item).getItemProperty("result").setValue(result);
				}
			
				if (resultBox.getValue().equals(ResponseValue.FAIL.ordinal()))
				{
					recommendBox.setValue(true);
					result.setRecommend(1);
					result.setResultsValue(ResponseValue.FAIL.ordinal()); 
				}
					
				else if (resultBox.getValue().equals(ResponseValue.PASS.ordinal()))
				{
					result.setResultsValue(ResponseValue.PASS.ordinal());
				}

				else if (resultBox.getValue().equals(ResponseValue.ONE.ordinal()))
				{
					result.setResultsValue(ResponseValue.ONE.ordinal());
				}

				else if (resultBox.getValue().equals(ResponseValue.TWO.ordinal()))
				{
					result.setResultsValue(ResponseValue.TWO.ordinal());
				}

				else if (resultBox.getValue().equals(ResponseValue.THREE.ordinal()))
				{
					result.setResultsValue(ResponseValue.THREE.ordinal());
				}

				else if (resultBox.getValue().equals(ResponseValue.FOUR.ordinal()))
				{
					result.setResultsValue(ResponseValue.FOUR.ordinal());
				}

				else if (resultBox.getValue().equals(ResponseValue.FIVE.ordinal()))
				{
					result.setResultsValue(ResponseValue.FIVE.ordinal());
				}

				else if (resultBox.getValue().equals(ResponseValue.SIX.ordinal()))
				{
					result.setResultsValue(ResponseValue.SIX.ordinal());
				}

				else if (resultBox.getValue().equals(ResponseValue.SEVEN.ordinal()))
				{
					result.setResultsValue(ResponseValue.SEVEN.ordinal());
				}

				else if (resultBox.getValue().equals(ResponseValue.EIGHT.ordinal()))
				{
					result.setResultsValue(ResponseValue.EIGHT.ordinal());
				}

				else if (resultBox.getValue().equals(ResponseValue.NINE.ordinal()))
				{
					result.setResultsValue(ResponseValue.NINE.ordinal());
				}

				else if (resultBox.getValue().equals(ResponseValue.TEN.ordinal()))
				{
					result.setResultsValue(ResponseValue.TEN.ordinal());
				}
				
				else if (resultBox.getValue().equals(ResponseValue.N_A.ordinal()))
				{
					result.setResultsValue(ResponseValue.N_A.ordinal());
				}
				
				getDataSource().updateResult(result);
				
				List<IGadget> gadgets = getApplicationContainer().getPage().getGadgets();
				
				for (IGadget gadget : gadgets)
				{
					if (gadget instanceof ClientDetailsGadget)
					{
						((ClientDetailsGadget) gadget).getBanner().calculateCompliance();
					}
					else if (gadget instanceof AssessmentGadget)
					{
						((AssessmentGadget) gadget).getBanner().calculateCompliance();
					}
				}
			}

I am getting the NullPointerException on line 88 when I don’t specify setNullSelectionAllowed, if that matters.

What could I be doing wrong? I have tried to mimic the examples using null values on vaadin.com, but I got the same result.

Thank you!

2

I just had a thought. Perhaps the setNullSelctionAllowed just allows a value of null to be returned for getValue(), but it does not actually have a selectable item in the list? I was thinking that it would have an item in the drop down list that could be selected and it would return null. Do I misunderstand how this works?

I must ask really unclear or really stupid questions, because I can hardly ever get a reply on my posts… :frowning: I am new to Java programming and Vaadin, so I am still just getting the basics down. I got thrown face first into a project and was told to learn it, so I need a little more help than the average developer.

Thanks!

3

It is my impression that setNullSelectionAllowed(true) just means that the user can select nothing, or if an item is selected, it can be unselected ctrl-clicking it.

You should get your blank choice no matter what, though, since you add it in. It’s unrelated to being null, though, as selecting the blank label will return -1 for its value.

So, if you select nothing at all, it should return null. If you call setNullSelectionItemId(-1), I believe that if the user also selects your blank element, you will get back null instead of the -1 value.

4

Thank you, David. I didn’t think about ctrl-clicking to deselect. The blank choice does go away when I set setNullSelectionAllowed(true) though with the -1 as the itemId. I am working through some alternatives to get it to behave the way I want it to. I think I just misunderstood the purpose of this method.

5

I think many people would do something like what you are doing, but instead of a blank choice for the option, use something like ‘-SELECT-’ mapping to your -1. You can still allow for null selection and setNullSelectionItemId(-1) – assuming it’s okay to not select anything and then if -SELECT- or nothing is chosen, you’ll get -1 as the value, otherwise the selected value.

6

Ok, I got it to work. What I had to do was remove the “-1” option altogether and it still left an empty/null value to select. I inherited the code I worked on from a more seasoned developer and the “-1” option was something he did. I figured he had it there for a reason, but I found that if I remove that item from the ComboBox altogether I get the result I want and no null pointer exception anymore. Thanks again for the guidance and ideas.