为什么我的文本区域没有更新？

Question

I've looked at similar threads here on SO, but whatever I do, the jTextArea won't update.

If I try something like:

for (int i = 0; i < a.getB().getC().size(); i++) {
        jTextArea1.append(a.getB().getC(i).toString()); 
        jTextArea1.update(jTextArea1.getGraphics());
    } 

I saw someone using getGraphics to resolve this problem, but it is not working in my case.

How can I make sure that the jTextArea is updated?

I've made sure that there's a value in the string as I print that to the console before trying to append it to the textarea.

Answer 1

Well, you should definitely not call update with the graphics of the textarea. Check this in order to understand update/getGraphics.

Check this for a solution: JTextArea's append () method doesn't seem to work

If it does not help, try to debug, perhaps you are appending an empty string or something like this.

Answer 2

Swing Components should be updated in EDT.

for (int i = 0; i < a.getB().getC().size(); i++) {

final int value = i;

SwingUtilities.invokeLater(new Runnable() {
    @Override
    public void run() {

        jTextArea1.append(a.getB().getC(value).toString()); 
    }
});
}

Answer 3

jTextArea.append should work. Maybe the update to the text area is blocked by some GUI action in the Swing Thread?

Answer 4

Apparantly the problem was that I created 2 instances of the GUI and one wasn't visible, so it would always exist behind the GUI that I could see, thus hiding the real problem.

When I found that out the problem was easy to solve. In my parentGUI where I create the other gui's, I now gave these new GUI's an instance of the parentGUI. See:

private void dropdownActionPerformed(java.awt.event.ActionEvent evt) {                                             
    if (dropdown.getSelectedIndex() == 1) {
        NewFrame newFrame = new NewFrame(this); //the keyword this did the trick
        newFrame.setVisible(true);
    }
}

Then in the constructor of NewFrame I catch the instance of the parentGUI:

public class NewFrame extends javax.swing.JFrame {

private GUI parentgui;

public NewFrame(GUI parentGUI) {
    initComponents();   
    parentgui = parentGUI;
}

And now our problem is solved :) I have only one instance of the parentGUI, and the jTextArea gets filled perfectly.