IntelliJ gui creator: JPanel gives runtime null pointer exception upon adding any component

Question

I am having a problem with IntelliJ's java gui creation. Most of the code behind the panel is unfortunately hidden within the gui creator and not editable by me.

I created a blank JPanel "questionPanel" with the ItelliJ GridLayoutManager. When I try to add anything to that panel, I get a null pointer exception even though the panel is definitely not null. I also tried adding a JTextField to the layout (out of curiosity) and that did not help either. The JTextField shows up, but I still cannot add anything from within the code.

When I change the layout manager to anything else (GridBagLayout, FormLayout, BorderLayout, etc.), I no longer get errors, but nothing shows up.

DisplayView.java

private JPanel questionPane;

public void initialize()
{
    questionPane.addMouseListener(new MouseListener() {

        @Override
        public void mouseReleased(MouseEvent e) {
            questionPane.add(new JLabel("Test"));
            System.out.println("Click event received.");
        }
        //other overrides hidden
}

Does anybody have an idea of what is going on behind the scenes or a way for me to get components onto the panel? Thanks.

Sample Stack Trace (this trace is not made by the same code as above, but it is the same error):

Exception occurred during event dispatching:
java.lang.NullPointerException

at com.intellij.uiDesigner.core.GridLayoutManager.addLayoutComponent(
GridLayoutManager.java:134)

at java.awt.Container.addImpl(Container.java:1074)
at java.awt.Container.add(Container.java:365)
at [MyProject].UI.View.DisplayView$1.actionPerformed(DisplayView.java:91)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:1995)
.....

For better help sooner, post an [SSCCE](http://sscce.org/). – Andrew Thompson Mar 10 '12 at 01:58 — Andrew Thompson, Mar 10 '12 at 01:58
maybe you checked custom create? – Radu Simionescu Mar 17 '14 at 19:13 — Radu Simionescu, Mar 17 '14 at 19:13

score 16 · Accepted Answer · answered May 15 '12 at 14:37

For anybody who is using IntelliJ's GUI creator and receiving the same error, I fixed the problem by manually setting the panel's layout manager in the code instead of choosing different layout managers within the GUI creator.

Example:

questionPane.setLayout(new BoxLayout(questionPane, BoxLayout.PAGE_AXIS));

score 4 · Answer 2 · answered Feb 16 '16 at 11:27

4

I've filed the issue as a bug on the JetBrains website and received the following answer:

For fix NPE, please add a child component to a JPanel with GridLayoutManager with GridConstraints like this:

panel.add(new JLabel(), new GridConstraints(...))

or use other layout.

Using the GridConstraints solved the problem for me just as using another LayoutManager.

I shortened & edited the answer for readability

answered Feb 16 '16 at 11:27

Peter

1,110
10
25

Where do you add that GridContraint? The exception happens when initializing the panel but I can't call panel.add until it is initialized. – Don May 07 '18 at 20:02

score 3 · Answer 3 · answered Jul 04 '15 at 15:55

I got the same error as you did. I have a JPanel with Layout Manager set to GridLayoutManager Intellij. When I tried to add any component to this panel, I was getting the exception.

I then went into the GUI editor and changed to BorderLayout and everything worked fine. I am not sure why it isn't working for you.

score 2 · Answer 4 · answered Jan 02 '20 at 15:10

I had the same error and after a tone of researching, I've got the point. the issue is you can't add a component to a JPanel if the Layout Manager of the JPanel is equal to GridLayoutManager(IntelliJ).

If you have the same problem.

Go to the GUI Designer
Select the JPanel that you want to add a component to it
From the properties panel, change the Layout Manager to anything but GridLayoutManager(IntelliJ) or FormLayout(JGoodies)

Or programmatically

contentPane.setLayout(new CardLayout());

score -1 · Answer 5 · answered Nov 26 '14 at 10:12

-1

The Intellij IDEA GUI creator also lets you insert images as labels. For that create a label anywhere you want, and in its cofigurations you'll find and icon slot where you'll choose the path to your image. And thats it!!

answered Nov 26 '14 at 10:12

Jorge Lima

157
15

IntelliJ gui creator: JPanel gives runtime null pointer exception upon adding any component

5 Answers5