Question

I have a problem with getting text from selected position of JComboBox. I tried to use getSelectedItem method in class which extends Kodowanie.java, but i get null value and i can’t find out why. Method (getSelectedItem) works in Kodowanie class I can easily get text form JComboBox .

Kodowanie.java

   public class Kodowanie {

        //Skladowe:
        ArrayList <String> qweqwe; 
        JComboBox inputCode = new JComboBox();  //HERE IS MY INPUT COMBOBOX
        JComboBox outputCode = new JComboBox();
        JTextArea input;
        JTextArea output;

    public void createGUI(){

        JFrame frame = new JFrame("Code");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        input  = new JTextArea(); 
        output = new JTextArea();

        qweqwe = new ArrayList<>();
        napelnijTalbiceCharsetami(qweqwe); //METHOD WHICH ADD ALL CHARSETS TO LIST

        inputCode = new JComboBox(qweqwe.toArray());
        outputCode = new JComboBox(qweqwe.toArray());

        JScrollPane scrollPaneInput = new JScrollPane(input, JScrollPane.VERTICAL_SCROLLBAR_ALWAYS, JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);
        JScrollPane scrollPaneOutput = new JScrollPane(output, JScrollPane.VERTICAL_SCROLLBAR_ALWAYS, JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);

        scrollPaneInput.setBorder(BorderFactory.createTitledBorder("Input Path"));
        scrollPaneOutput.setBorder(BorderFactory.createTitledBorder("Output Path"));

        inputCode.setPreferredSize(new Dimension(400,50));
        outputCode.setPreferredSize(new Dimension(400,50));

        scrollPaneInput.setPreferredSize(new Dimension(400, 100));
        scrollPaneOutput.setPreferredSize(new Dimension(400, 100));

        input.addKeyListener(new KeyAdapter() {
             public void keyPressed(KeyEvent evt){  
                    Strumieniowanie tmp;
                    if(evt.getKeyCode() == KeyEvent.VK_ENTER)
                    {
                        try {
                            tmp = new Strumieniowanie(input.getText(), output.getText());
                        } catch (IOException e) {
                            // TODO Auto-generated catch block
                            e.printStackTrace();
                        }
                    }
                }
        });

        frame.getContentPane().add(scrollPaneInput);
        frame.getContentPane().add(scrollPaneOutput);
        frame.getContentPane().add(inputCode);
        frame.getContentPane().add(outputCode);

        frame.setLayout(new  FlowLayout());
        frame.setPreferredSize(new Dimension(850, 220));
        frame.setVisible(true);
        frame.pack();

    }

    private ArrayList napelnijTalbiceCharsetami(ArrayList tmp){
        Map charSets = Charset.availableCharsets();
        Iterator iterator = charSets.keySet().iterator();
        while (iterator.hasNext()) {
            System.out.println(iterator.next().toString());
            tmp.add(iterator.next().toString());
        }
        return tmp;
    }



    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Kodowanie l = new Kodowanie();
        l.createGUI();
    }



}

Strumieniowanie.java

public class Strumieniowanie extends Kodowanie {

    protected boolean pathInputOk = false;
    protected boolean pathOutputOk = false;

public Strumieniowanie(String tmpInpute, String tmpOutput) throws IOException {


    File plikInput = new File(tmpInpute);
    File plikOutput = new File(tmpOutput);

    String inputText;
    inputText =  (String) inputCode.getSelectedItem(); //HERE I TRY TO GET STRING FROM JCOMBOBOX BUT IT IS ALWAYS NULL !
    System.out.println(inputText);

    pathInputOk = plikInput.isFile();
    pathOutputOk = plikOutput.isFile();

    System.out.println(pathInputOk);
    System.out.println(pathOutputOk);

    if (pathInputOk && pathOutputOk) {
        File nowyPlik = new File(tmpInpute);

        FileInputStream fis = new FileInputStream(nowyPlik);

        fis.close();

    }

}

protected boolean isItaPath(File plik) {
    boolean tmp = 

false;
        tmp = plik.isFile();

        return tmp;
    }


}

Answer 1

KeyListener is not the appropriate event listener to use, it is triggered BEFORE the combobox has updated its state, better to use an ActionListener.

The actionPerformed event will be fired AFTER the combo box has updated, which will ensure that the getSelectedItem method will actually return the currently selected value.