P4
Imagine putting a List into a Panel, and that the list is initially
empty. It will be sized without scrollbars to fit inside the Panel's
insets.
Now imagine adding entries to the list. At some point, the list will
have more entries than were initially allowed for, and/or some of the
entries may be longer than initially allowed for.
Motif handles this by adding scrollbars to the underlying List widget.
However, AWT does not notice the addition of the scrollbars. This
means that the size() of the List component is incorrect once the
scrollbars are added, and that the List does not layout correctly with
respect to its parent and/or siblings.
Attached is a simple demo applet, that can be run under JDK beta.
Initially it shows a red panel, correctly containing an empty grey
list, surrounded by a green rectangle that indicates the panel's
insets. A thread runs, slowly adding entries to the list. These
entries report the current size of the List, and contain padding so
that the entries are successively longer and longer. First, a
horizontal scrollbar is added by AWT/Motif, and then a vertical
scrollbar is added. These scrollbars incorrectly overflow the panels
insets. Furthermore, even though the List component gets visibly
bigger, the width and height reported in the successive entries of the
list are constant, reflecting the size of the component before the
scrollbars were added.
---------Bug.java-------------------------------------
import java.applet.Applet;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Insets;
import java.awt.List;
import java.awt.Panel;
public class Bug extends Applet implements Runnable
{
public void init() {
Panel p = new MyPanel();
p.add(list = new List(10, false));
add(p);
new Thread(this).start();
}
synchronized public void run() {
try {
for (int i = 0; i < 20; i++) {
Dimension d = list.size();
String s = ("row " + i + " w=" + d.width + " h=" + d.height);
for (int j = 0; j < i; j++)
s += ".";
list.addItem(s);
wait(1000);
}
}
catch (InterruptedException e) {
System.out.println("Interrupted!");
}
}
List list;
}
class MyPanel extends Panel
{
public Insets insets() {
return new Insets(20, 20, 20, 20);
}
public void paint(Graphics g) {
Dimension dims = size();
Insets i = insets();
g.setColor(Color.red);
g.fillRect(0, 0, dims.width-1, dims.height -1);
g.setColor(Color.green);
g.drawRect(i.left, i.top,
dims.width - i.left - i.right - 1, dims.height - i.top - i.bottom - 1);
}
}
-------------------test.html----------------------------
<html>
<head>
<TITLE>List bug demo</TITLE>
</head>
<body>
<applet
codebase=/home/jjg/javatest/src/javatest/bug
code="Bug.class"
width=200
height=200
>
LIST RESIZING BUG DEMO
</applet>
</body>
</html>
[richie 3/4/97]
New info from IBM sheds some more information and a proposed fix to this bug.
If you run the following program with the 1.1 appletviewer on Solaris
(or AIX) and click on the Add button until the List component
"overflows", the scrollbar does now appear (it didn't appear at all on
1.0.2), but in the wrong place - to the right of the component on top
of any other components which may be there, not inside it as on
Windows NT. To make matters worse, if the applet is resized the
scrollbar jumps inside the component. This seems to be a fairly major
problem in the development of a complex cross platform GUI (as a team
in IBM Austin is trying to do), so we'd be grateful you could have a
look at this.
I realise this is a problem with the use of the Motif toolkit, but as
it gets it right after a resize, surely there is a way to get the
correct behaviour when items are added.
Also please let me know if you find any work-around for this that can
be used within the applet code, by subclassing List for example.
listTest.html:
--snip--
<applet code=listTest width=300 height=200>
</applet>
--snip--
listTest.java:
--snip--
import java.applet.*;
import java.awt.*;
public class listTest extends Applet {
List list;
Button addButton;
Button delButton;
int item=0;
public void init() {
super.init();
setLayout(new GridLayout(1,2));
list = new List();
add(list);
Panel pan;
add(pan = new Panel());
pan.setLayout(new GridLayout(4,1));
addButton = new Button("Add List Item");
pan.add(addButton);
delButton = new Button("Delete List Item");
pan.add(delButton);
}
public boolean action(Event evt, Object o) {
if (evt.target == addButton) {
list.addItem("item" + Integer.toString(item++));
return(true);
} else if (evt.target == delButton) {
int i;
if ((i = list.countItems()) > 0) {
list.delItem(i - 1);
--item;
}
return(true);
}
return(false);
}
}
empty. It will be sized without scrollbars to fit inside the Panel's
insets.
Now imagine adding entries to the list. At some point, the list will
have more entries than were initially allowed for, and/or some of the
entries may be longer than initially allowed for.
Motif handles this by adding scrollbars to the underlying List widget.
However, AWT does not notice the addition of the scrollbars. This
means that the size() of the List component is incorrect once the
scrollbars are added, and that the List does not layout correctly with
respect to its parent and/or siblings.
Attached is a simple demo applet, that can be run under JDK beta.
Initially it shows a red panel, correctly containing an empty grey
list, surrounded by a green rectangle that indicates the panel's
insets. A thread runs, slowly adding entries to the list. These
entries report the current size of the List, and contain padding so
that the entries are successively longer and longer. First, a
horizontal scrollbar is added by AWT/Motif, and then a vertical
scrollbar is added. These scrollbars incorrectly overflow the panels
insets. Furthermore, even though the List component gets visibly
bigger, the width and height reported in the successive entries of the
list are constant, reflecting the size of the component before the
scrollbars were added.
---------Bug.java-------------------------------------
import java.applet.Applet;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Insets;
import java.awt.List;
import java.awt.Panel;
public class Bug extends Applet implements Runnable
{
public void init() {
Panel p = new MyPanel();
p.add(list = new List(10, false));
add(p);
new Thread(this).start();
}
synchronized public void run() {
try {
for (int i = 0; i < 20; i++) {
Dimension d = list.size();
String s = ("row " + i + " w=" + d.width + " h=" + d.height);
for (int j = 0; j < i; j++)
s += ".";
list.addItem(s);
wait(1000);
}
}
catch (InterruptedException e) {
System.out.println("Interrupted!");
}
}
List list;
}
class MyPanel extends Panel
{
public Insets insets() {
return new Insets(20, 20, 20, 20);
}
public void paint(Graphics g) {
Dimension dims = size();
Insets i = insets();
g.setColor(Color.red);
g.fillRect(0, 0, dims.width-1, dims.height -1);
g.setColor(Color.green);
g.drawRect(i.left, i.top,
dims.width - i.left - i.right - 1, dims.height - i.top - i.bottom - 1);
}
}
-------------------test.html----------------------------
<html>
<head>
<TITLE>List bug demo</TITLE>
</head>
<body>
<applet
codebase=/home/jjg/javatest/src/javatest/bug
code="Bug.class"
width=200
height=200
>
LIST RESIZING BUG DEMO
</applet>
</body>
</html>
[richie 3/4/97]
New info from IBM sheds some more information and a proposed fix to this bug.
If you run the following program with the 1.1 appletviewer on Solaris
(or AIX) and click on the Add button until the List component
"overflows", the scrollbar does now appear (it didn't appear at all on
1.0.2), but in the wrong place - to the right of the component on top
of any other components which may be there, not inside it as on
Windows NT. To make matters worse, if the applet is resized the
scrollbar jumps inside the component. This seems to be a fairly major
problem in the development of a complex cross platform GUI (as a team
in IBM Austin is trying to do), so we'd be grateful you could have a
look at this.
I realise this is a problem with the use of the Motif toolkit, but as
it gets it right after a resize, surely there is a way to get the
correct behaviour when items are added.
Also please let me know if you find any work-around for this that can
be used within the applet code, by subclassing List for example.
listTest.html:
--snip--
<applet code=listTest width=300 height=200>
</applet>
--snip--
listTest.java:
--snip--
import java.applet.*;
import java.awt.*;
public class listTest extends Applet {
List list;
Button addButton;
Button delButton;
int item=0;
public void init() {
super.init();
setLayout(new GridLayout(1,2));
list = new List();
add(list);
Panel pan;
add(pan = new Panel());
pan.setLayout(new GridLayout(4,1));
addButton = new Button("Add List Item");
pan.add(addButton);
delButton = new Button("Delete List Item");
pan.add(delButton);
}
public boolean action(Event evt, Object o) {
if (evt.target == addButton) {
list.addItem("item" + Integer.toString(item++));
return(true);
} else if (evt.target == delButton) {
int i;
if ((i = list.countItems()) > 0) {
list.delItem(i - 1);
--item;
}
return(true);
}
return(false);
}
}
- duplicates
-
JDK-1238724 vertical scrollbar will not appear correctly when adding new items to list
-
- Closed
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- Closed
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