Changing JScollPane view

What i want to happen when the text the user typed onto the JTextArea gets too large for the viewport, is for the view in the viewport to be on the right hand side of the JTextArea so the user can see what they just typed instead of it staying on the left hand side of the JTextArea.

Here's a little exacutable program which demonstates the problem (as well as a few others which don't seem to be present in my full program):

Code:

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import java.awt.*;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.util.LinkedList;
import javax.swing.*;

public class OutputDisplayFrame extends JFrame{
        //class objects
        private KeyListenerClass keyListener;
        //variables
        private JPanel mainPanel;
        private JTextArea display;
        private JScrollPane displayPanelScrollPane;
        private LinkedList<String> displayText = new LinkedList<String>();
        private int lineCounter = 0;
        private final int DIGIT_WIDTH = 30, MARGIN_WIDTH = 30;
        private JViewport viewport;
        private Component view;
        private String displayString = "";
       
        //main method
        public static void main(String args[]){
                new OutputDisplayFrame();
        }
       
        //constructor
        public OutputDisplayFrame(){
                //setting frame
                this.setTitle("Calculator");
                this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                this.setSize(800, 600);
                this.setVisible(true);
               
                //setting panel
                mainPanel = new JPanel();
                mainPanel.setBorder(BorderFactory.createEmptyBorder(30, 30, 30, 30));
               
                //setting JScrollPane
                displayPanelScrollPane = new JScrollPane(mainPanel);
                this.add(displayPanelScrollPane);
               
                //setting mainPanel
                mainPanel.setBackground(Color.WHITE);
                mainPanel.setLayout(new BorderLayout());
               
                //setting display
                display = new JTextArea();
                display.setEditable(false);
                display.setOpaque(false);
                display.setFont(new Font(Font.SANS_SERIF, Font.BOLD, 40));
                display.setTabSize(2);
                mainPanel.add(display, BorderLayout.CENTER);
               

                //////////////////////////////////setting default scrollPane position///////////////////////////////////////////
                viewport = displayPanelScrollPane.getViewport();
                view = viewport.getView();
                viewport.setViewPosition(new Point(0, view.getHeight()));

           
                //adding object to linked list
                displayText.add("");
               
                this.setFocusable(true);
               
                //add keyListener
                keyListener = new KeyListenerClass();
                this.addKeyListener(keyListener);
        }
       
        //OutputDisplayInterface methods
        public void addText(String displayString){
                //saving new string
                displayText.remove(lineCounter);
                displayText.add(displayString);
               
                //formatting test
                String formatedText = "";
               
                for(int i = 0; i <= lineCounter; i++){
                        formatedText += displayText.get(i);
                        formatedText += "\n";
                }
               
                display.setText(formatedText);
               
                //changing focus position of scrollPane if the current line of working is wider than the frame
                if(displayText.peekLast().length() * DIGIT_WIDTH - MARGIN_WIDTH * 2 > this.getWidth()){
                       
                       
                        /////////////////////////////////////changing the view of the viewport////////////////////////////////////////////////
                       
                        System.out.println(new Point(view.getWidth(), view.getHeight()));
                       
                        viewport.setViewPosition(new Point(view.getWidth(), view.getHeight()));
                        display.revalidate();
                       
                        System.out.println(viewport.getViewPosition());
                       
                       
                }
                       
        }
       
        public void clear(){
                //clearing linked list
                displayText.clear();
                lineCounter = 0;
                displayText.add("");
               
                //resetting display
                display.setText("");
               
                //setting default scrollPane position
                viewport.setViewPosition(new Point(0, view.getHeight()));
        }
       
        public void newLine(){
                displayText.add("");
               
                //setting default scrollPane position
                viewport.setViewPosition(new Point(0, view.getHeight()));
               
                lineCounter++;
        }
       
        private void setTopDisplayString(String s){
                displayString += s;
                addText(displayString);
        }
       
        //private class
       
        private class KeyListenerClass implements KeyListener{
                public void keyPressed(KeyEvent event) {
                        int keyCode = event.getKeyCode();
                       
                        if(keyCode == KeyEvent.VK_DELETE)
                                clear();
                        else if(keyCode == KeyEvent.VK_A)
                                setTopDisplayString("Ans");
                        else if(keyCode == KeyEvent.VK_DIVIDE)
                                setTopDisplayString("/");
                        else if(keyCode == KeyEvent.VK_1 || keyCode == KeyEvent.VK_NUMPAD1)
                                setTopDisplayString("1");
                        else if(keyCode == KeyEvent.VK_2 || keyCode == KeyEvent.VK_NUMPAD2)
                                setTopDisplayString("2");
                        else if(keyCode == KeyEvent.VK_3 || keyCode == KeyEvent.VK_NUMPAD3)
                                setTopDisplayString("3");
                        else if(keyCode == KeyEvent.VK_MULTIPLY)
                                setTopDisplayString("*");
                        else if(keyCode == KeyEvent.VK_4 || keyCode == KeyEvent.VK_NUMPAD4)
                                setTopDisplayString("4");
                        else if(keyCode == KeyEvent.VK_5 || keyCode == KeyEvent.VK_NUMPAD5)
                                setTopDisplayString("5");
                        else if(keyCode == KeyEvent.VK_6 || keyCode == KeyEvent.VK_NUMPAD6)
                                setTopDisplayString("6");
                        else if(keyCode == KeyEvent.VK_MINUS || keyCode == KeyEvent.VK_SUBTRACT)
                                setTopDisplayString("-");
                        else if(keyCode == KeyEvent.VK_7 || keyCode == KeyEvent.VK_NUMPAD7)
                                setTopDisplayString("7");
                        else if(keyCode == KeyEvent.VK_8 || keyCode == KeyEvent.VK_NUMPAD8)
                                setTopDisplayString("8");
                        else if(keyCode == KeyEvent.VK_9 || keyCode == KeyEvent.VK_NUMPAD9)
                                setTopDisplayString("9");
                        else if(keyCode == KeyEvent.VK_ADD)
                                setTopDisplayString("+");
                        else if(keyCode == KeyEvent.VK_0 || keyCode == KeyEvent.VK_NUMPAD0)
                                setTopDisplayString("0");
                        else if(keyCode == KeyEvent.VK_EQUALS || keyCode == KeyEvent.VK_ENTER){
                                newLine();
                                displayString = "";
                        }
                }
               
                public void keyReleased(KeyEvent event) {}
                public void keyTyped(KeyEvent event) {}
        }
}

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Any help would be appresiated.

Disclaimer: I haven't gone through your code since it obviously contains a whole lot of stuff that's unrelated to the problem. To get better help sooner, post a SSCCE (Short, Self Contained, Compilable and Executable) example.

Code:

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JScrollBar scrollBar = scrollPane.getHorizontalScrollBar();
scrollBar.setValue(scrollBar.getMaximum());

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Or you may want to use the approach in camickr's Left Dot Renderer « Java Tips Weblog

db

Incidentally, why are you using a JLabel and not a JTextField with setEditable(false)? With the latter, you could set the caret position.

db

I'm accually using a JTextArea in the program, sorry for cofussing you. Setting the scrollBar value didn't make any difference. I'll see where i can get with caret position but i haven't used any caret methods before.

I can't seem to get anywhere with the caret idea but i don't realy know what i'm doing.

Quote:

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Originally Posted by peterhabe

I'm accually using a JTextArea in the program, sorry for cofussing you. Setting the scrollBar value didn't make any difference. I'll see where i can get with caret position but i haven't used any caret methods before.

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Darryl didn't say to use JTextArea, please re-read his post.

Quote:

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I can't seem to get anywhere with the caret idea but i don't realy know what i'm doing.

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And we don't know what you're doing either since you're not showing us your code attempt and any error messages, etc...

If you're still stuck, post an SSCCE that shows your latest attempt, and let's work with it with you.

Quote:

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Originally Posted by Fubarable

Darryl didn't say to use JTextArea, please re-read his post.

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In origonal first post in this thread i said i was using JLabel to display the text when i was accually using a JTextArea (as pointed out in my reason for editing). Again sorry for any confussion.

Quote:

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Originally Posted by Fubarable

And we don't know what you're doing either since you're not showing us your code attempt and any error messages, etc...

If you're still stuck, post an SSCCE that shows your latest attempt, and let's work with it with you.

---

I did mange to get the getCaretPosition() method running in the end but it doesn't change the view of the JViewPort. Also as my text will be covering more than one line i don't think it will be of much use.

There is the code for the SSCCE of my latest attempt which i've stipped down a bit more from the origonal code i posted:

Code:

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import java.awt.*;
import java.awt.event.*;
import java.util.LinkedList;
import javax.swing.*;

public class OutputDisplayFrame extends JFrame implements KeyListener{
        //variables
        private JPanel mainPanel = new JPanel();
        private JTextArea displayTextField = new JTextArea();
        private JScrollPane displayPanelScrollPane = new JScrollPane(mainPanel);
        private LinkedList<String> displayText = new LinkedList<String>();
        private int lineCounter = 0;
        private final int DIGIT_WIDTH = 7;
        private JViewport viewport;
        private Component view;
        private String displayString = "";
       
        //main method
        public static void main(String args[]){
                new OutputDisplayFrame();
        }
       
        //constructor
        public OutputDisplayFrame(){
                //setting frame
                this.setTitle("Calculator");
                this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                this.setSize(800, 600);
                this.setVisible(true);
               
                //adding JScrollPane
                this.add(displayPanelScrollPane);
               
                //setting mainPanel
                mainPanel.setLayout(new BorderLayout());
               
                //setting display JTextArea
                displayTextField.setEditable(false);
                mainPanel.add(displayTextField, BorderLayout.CENTER);
               
                viewport = displayPanelScrollPane.getViewport();
                view = viewport.getView();
           
                //adding new string to linked list
                displayText.add("");
               
                //add keyListener
                this.addKeyListener(this);
                this.setFocusable(true);
        }
       
        public void addText(String displayString){
                //saving new string to displayText LinkedList
                displayText.remove(lineCounter);
                displayText.add(displayString);
               
                //formatting test
                String formatedText = "";
               
                for(int i = 0; i <= lineCounter; i++){
                        formatedText += displayText.get(i);
                        formatedText += "\n";
                }
               
                //setting JTextField
                displayTextField.setText(formatedText);
               
                //changing view of scrollPane if the current line of working is wider than the frame
                if(displayText.peekLast().length() * DIGIT_WIDTH > this.getWidth()){
                       
                       
                        /////////////////////////////////////trying to change the view of the JViewport////////////////////////////////////////////////
                        viewport.setViewPosition(new Point(displayTextField.getCaretPosition() * DIGIT_WIDTH, view.getHeight()));
                        //displayPanelScrollPane.getHorizontalScrollBar().setValue(displayPanelScrollPane.getHorizontalScrollBar().getMaximum());
                        viewport.revalidate();
                       
                        System.out.println("getCaretPosition() * DIGIT_WIDTH: "+displayTextField.getCaretPosition() * DIGIT_WIDTH);
                        System.out.println("Point passed into setViewPosition(): "+new Point(view.getWidth(), view.getHeight()));
                        System.out.println("Current view position: "+viewport.getViewPosition()+"\n");
                       
                       
                }       
        }
       
        //KeyListener methods
        public void keyPressed(KeyEvent event) {
                int keyCode = event.getKeyCode();
               
                if(keyCode == KeyEvent.VK_DELETE){
                        clear();
                }else if(keyCode == KeyEvent.VK_EQUALS || keyCode == KeyEvent.VK_ENTER){
                        newLine();
                        displayString = "";
                }else{
                        addToDisplayString(String.valueOf(keyCode));
                }
        }
               
        public void keyReleased(KeyEvent event) {}
        public void keyTyped(KeyEvent event) {}
       
        //clears displayTextField
        public void clear(){
                //clearing displayText LinkedList
                displayText.clear();
                lineCounter = 0;
                displayText.add("");
               
                //resetting display
                displayTextField.setText("");
               
                //setting default scrollPane view
                viewport.setViewPosition(new Point(0, view.getHeight()));
        }
               
        //starts new line in DisplayTextField
        public void newLine(){
                //adding new String to linked list
                displayText.add("");
               
                //setting default scrollPane view
                viewport.setViewPosition(new Point(0, view.getHeight()));
               
                lineCounter++;
        }
       
        private void addToDisplayString(String s){
                displayString += s;
                addText(displayString);
        }
}

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And here is the printouts that are displayed in the console when the program tries to change the view of the JViewport from its default view:

getCaretPosition() * DIGIT_WIDTH: 826
Point passed into setViewPosition(): java.awt.Point[x=798,y=544]
Current view position: java.awt.Point[x=17,y=544]

getCaretPosition() * DIGIT_WIDTH: 847
Point passed into setViewPosition(): java.awt.Point[x=819,y=544]
Current view position: java.awt.Point[x=38,y=544]

You don't need to setViewPosition, just use the methods of DefaultCaret with a policy of ALWAYS_UPDATE. Take a look at camickr's blog page on Text Area Scrolling « Java Tips Weblog

db

I've tried both methods suggested in that post, putting

Code:

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DefaultCaret caret = (DefaultCaret)displayTextArea.getCaret();
caret.setUpdatePolicy(DefaultCaret.ALWAYS_UPDATE);

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in the constructor and putting

Code:

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displayTextArea.append("");
displayTextArea.setCaretPosition(displayTextArea.getDocument().getLength());

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every time the size of the JTextArea is enlarged, but the horizontal scroll bar just won't budge. The vertical scroll bar scrolls down without a problem.

Thanks for the help so far DarrylBurke, its much appreciated.