java 如何从 JComboBox 获取文本？

How to get text from JComboBox?

提问by mathewM

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 .

我在从 JComboBox 的选定位置获取文本时遇到问题。我试图在扩展 Kodowanie.java 的类中使用 getSelectedItem 方法，但我得到空值，我找不到原因。方法 (getSelectedItem) 在 Kodowanie 类中有效，我可以轻松地从 JComboBox 获取文本形式。

Kodowanie.java

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

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;
    }


}

回答by MadProgrammer

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

KeyListener不是要使用的适当事件侦听器，它在组合框更新其状态之前触发，最好使用ActionListener.

The actionPerformedevent will be fired AFTER the combo box has updated, which will ensure that the getSelectedItemmethod will actually return the currently selected value.

该actionPerformed事件将在组合框更新后触发，这将确保该getSelectedItem方法实际返回当前选定的值。

回答by Kapil Garg

The following method can be used to get the text from a ComboBox.

以下方法可用于从ComboBox.

String s = (String)comboOne.getSelectedItem();

where comboOneis the variable name of ComboBox.

comboOne的变量名在哪里ComboBox。

回答by Alexandre Fradkin

For reference, to answer the tittle of the page : How to get text from JComboBox?

作为参考，回答页面标题：How to get text from JComboBox?

((JTextComponent)combo.getEditor().getEditorComponent()).getText()

It "works" but does not return any text... crap.

它“有效”但不返回任何文本......废话。