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scrollpane and scrollbar

Posted on 2001-06-14
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Last Modified: 2010-03-31
i wonder how to control a scrollbar together with a scrollpane? can any one provide me a simple example on this.

what if i want the scrollbar to always scroll down to the last page/end of file, what should i do? can any provide me the example/source on this?
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Question by:cys050200
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6 Comments
 
LVL 1

Expert Comment

by:saurav17
ID: 6193962


hi,
pls., be clear on what u r saying.
I dont get ur concept., Could u give me more details abt., what u want.


regards,
K.J.S.
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LVL 9

Expert Comment

by:Ovi
ID: 6193963
simply set all the time the caret from your text object used for displaying to point to the end of the document, call an scroll.updateUI(); and that's all.
0
 
LVL 1

Expert Comment

by:saurav17
ID: 6193976


hi,
pls., be clear on what u r saying.
I dont get ur concept., Could u give me more details abt., what u want.


regards,
K.J.S.
0
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Author Comment

by:cys050200
ID: 6194209
for example, here are some codes for a class which extends JFrame:

 JTextArea outputArea = new JTextArea(30,60);
 JScrollPane scroller = new JScrollPane(outputArea);
 String str = "xxxx" ; //the str may be very long

 scroller.setAutoscrolls(true);
 outputArea.setAutoscrolls(true);
 outputArea.setText(str);
 
 Container c = getContentPane();
 c.setLayout(new BorderLayout());
 c.add(scroller,BorderLayout.CENTER);

 my question is, in the above situation, why is that my output(the scroller) is not scrolled down automatically if the str input is very long(longer than a page, for example).
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LVL 9

Accepted Solution

by:
Ovi earned 300 total points
ID: 6194409
Do'it like this :

JTextArea outputArea = new JTextArea(30,60);
JScrollPane scroller = new JScrollPane(outputArea);
String str = "xxxx" ; //the str may be very long

scroller.setAutoscrolls(true);
outputArea.setAutoscrolls(true);
outputArea.setText(str);
updateScroll();

Container c = getContentPane();
c.setLayout(new BorderLayout());
c.add(scroller,BorderLayout.CENTER);
.....

private void updateScroll() {
outputArea.setCaretPosition(outputArea.getText().length() - 1);
}

Every time you update the text or append some text to your JTextArea call updateScroll() method.
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LVL 9

Expert Comment

by:Ovi
ID: 6194418
you may need an try/catch in the method updateScroll for invalid location like this :

private void updateScroll() {
  try {
    outputArea.setCaretPosition(outputArea.getText().length() - 1);
  catch(Exception e) {
    System.out.println(e.toString());
  }
}

What is done at setCaretLocation ? The caret position is updated after that is build an Rectangle object based on the new location and called the scrollPane method scrollRectToVisible(Rectangle r)
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