JButton 在 JScrollPane 上

Question

I have such piece of code which shoud add button over JTextArea placed in JScrollPane . Button isn't inside scroll pane!

    JScrollPane scrollPane = new JScrollPane();
    scrollPane.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
    scrollPane.setBounds(10, 340, 375, 242);
    contentPane.add(scrollPane);

    JButton btnClean = new JButton();
    btnClean.setBounds(340, 341, 26, 23);
    contentPane.add(btnClean);

    taLog = new JTextArea();
    taLog.setEditable(false);
    taLog.setLineWrap(true);
    taLog.setFont(new Font("Arial", Font.PLAIN, 12));
    scrollPane.setViewportView(taLog);

    epInfo = new JEditorPane();
    epInfo.putClientProperty(JEditorPane.HONOR_DISPLAY_PROPERTIES, Boolean.TRUE);
    epInfo.setFont(new Font("Tahoma", Font.PLAIN, 12));
    epInfo.setContentType("text/html");
    epInfo.setEditable(false);
    epInfo.setBackground(null);
    epInfo.setBorder(null);
    epInfo.setBounds(10, 241, 375, 37);
    setInfoText();
    contentPane.add(epInfo);

Problem is whenever JTextArea changes its value button is not refreshed - it just dissapears - until I will drag mouse cursor over it. I suppose then some repaint() is launched.
I figured out I can add DocumentListener to JTextArea and there manually refresh button but it works until scroll bar appears in JScrollPane . I can also use

scrollPane.getViewport().addChangeListener(new ChangeListener() {
@Override
public void stateChanged(ChangeEvent e)
{}});

but it is invoked many times and all those refreshes are not neccesary. Is there any reasonable (and efficient) way to check if JScrollPane changed?

Answer 1

Null layout is useful in this case because main window is fixed

No it is not useful.

Any time you code uses random numbers (ie to set the size/location) of components) the code is not easily maintainable.

Also I use WindowBuilder

Code generated by an IDE is not maintainable in another IDE.

Learn to use layout managers. The point of using layout managers is to avoid hard coding of numbers and to make the code maintainable in any environment.

Problem is whenever JTextArea changes its value button is not refreshed

contentPane.add(scrollPane);
...
contentPane.add(btnClean);

Swing is designed to display components in two dimension when added to the same container.

If you want components displayed in two dimension then you need to have a parent / child relationship:

- content pane
    - text area
        button

So the code should be something like:

textArea.setLayout( new FlowLayout(FlowLayout.RIGHT) );
//contentPane.add(btnClean);
textArea.add(btnClean);

Note: you can configure the FlowLayout to remove the spacing on the top and right.

The problem with this is that the button will cover any text that displayed in the text area.

So the better solution is to make the button external to the text area.