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I have a JScrollPane whose content pane is a JXList. When I use the mouse wheel on the list, the list steps three (3) items at a time. This also works for a table, regardless of row height. How can I change this so that - regardless of platform - for both list and table the scroll distance is exactly 1 item? Setting block increment doesn't cut it because some rows in the table have a different height.
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Just use the reference to your JScrollPane object, get the vertical scroll bar from it using getVerticalScrollBar , and then call setUnitIncrement on it, like this: myJScrollPane. getVerticalScrollBar().
A JScrollPane provides a scrollable view of a component. When screen real estate is limited, use a scroll pane to display a component that is large or one whose size can change dynamically. Other containers used to save screen space include split panes and tabbed panes.
Out of pure interest (and a little boredom) I created a working example:
/**
* Scrolls exactly one Item a time. Works for JTable and JList.
*
* @author Lukas Knuth
* @version 1.0
*/
public class Main {
private JTable table;
private JList list;
private JFrame frame;
private final String[] data;
/**
* This is where the magic with the "just one item per scroll" happens!
*/
private final AdjustmentListener singleItemScroll = new AdjustmentListener() {
@Override
public void adjustmentValueChanged(AdjustmentEvent e) {
// The user scrolled the List (using the bar, mouse wheel or something else):
if (e.getAdjustmentType() == AdjustmentEvent.TRACK){
// Jump to the next "block" (which is a row".
e.getAdjustable().setBlockIncrement(1);
}
}
};
public Main(){
// Place some random data:
Random rnd = new Random();
data = new String[120];
for (int i = 0; i < data.length; i++)
data[i] = "Set "+i+" for: "+rnd.nextInt();
for (int i = 0; i < data.length; i+=10)
data[i] = "<html>"+data[i]+"<br>Spacer!</html>";
// Create the GUI:
setupGui();
// Show:
frame.pack();
frame.setVisible(true);
}
private void setupGui(){
frame = new JFrame("Single Scroll in Swing");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
JSplitPane split = new JSplitPane(JSplitPane.HORIZONTAL_SPLIT);
frame.add(split);
// Add Data to the table:
table = new JTable(new AbstractTableModel() {
@Override
public int getRowCount() {
return data.length;
}
@Override
public int getColumnCount() {
return 1;
}
@Override
public Object getValueAt(int rowIndex, int columnIndex) {
return data[rowIndex];
}
});
for (int i = 0; i < data.length; i+=10)
table.setRowHeight(i, 30);
JScrollPane scroll = new JScrollPane(table);
// Add out custom AdjustmentListener to jump only one row per scroll:
scroll.getVerticalScrollBar().addAdjustmentListener(singleItemScroll);
split.add(scroll);
list = new JList<String>(data);
scroll = new JScrollPane(list);
// Add out custom AdjustmentListener to jump only one row per scroll:
scroll.getVerticalScrollBar().addAdjustmentListener(singleItemScroll);
split.add(scroll);
}
public static void main(String[] agrs){
new Main();
}
}
The real magic is done in the custom AdjustmentListener, where we go and increase the current "scroll-position" by one single block per time. This works up and down and with different row-sizes, as shown in the example.
As @kleopatra mentioned in the comments, you can also use a MouseWheelListener to only redefine the behavior of the mouse-wheel.
See the official tutorial here.
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