Question

Hy everyone,

I’m trying to do some calculations in a JTable after iteration and mark with different background the cells that I need.

However, I have 2 problems at the moment:
1) Cells are not painted immediately, but after the whole iteration cycle
2) Areas are not painted properly – if I need to paint table[3, 4] and table[6, 5] it draws a rectangular from [3,4] up to [6, 5] instead of drawing the singular cells only.

About problem 1: could I call repaint() with priority without the need to finish everything and the JVM to decide whenever to paint? I try to do fireTableCellUpdated() and fireTableDataChanged() but they don’t get updated.

Here there is my custom cell renderer method that changes the BGcolor:

public Component getTableCellRendererComponent(JTable table, Object value,
    boolean isSelected, boolean hasFocus, int row,int column) {
    Component renderer = super.getTableCellRendererComponent(
        table, value, isSelected, hasFocus, row, column);

    if(value instanceof Color) {
        Color c = (Color) value;
        renderer.setBackground(c);
        System.out.println("BG change [" + row + ":" + column + "]");
    }

    return renderer;
}

Here there is the loop where I paint my cells on a button click:

for(int paintJ = startIndex; paintJ < endIndex; paintJ++) {
     CrossCellRenderer rend =  (CrossCellRenderer) jTable1.getCellRenderer(i,  paintJ)
           .getTableCellRendererComponent(jTable1, Color.blue, true, true, i, paintJ);
     crossTableModel.fireTableCellUpdated(i, paintJ);
     jTable1.revalidate();
     jTable1.repaint();
     try {
          Thread.sleep(1000);
     }   catch(InterruptedException ie) {
           System.err.println("Exception sleeping the thread.");
     }
 }

Any tips on that?

Answer 1

Hate to say: but you do it (whatever you want to reach) completely wrong 😉

• Never-ever do any direct manipulation/paint on a renderer, instead change the model data and the rest will happen automatically.
• Never-ever call any of the fireXX methods on a model from outside the model, it’s the exclusive responsibility of the model to notify
  its listeners on change
• Never-ever (or very very rarely, certainly not here 😉 there’s a need to call revalidate and/or repaint dircectly, will happen
  automatically if a model is well-behaved
• ….

Best to read Snoracle’s tutorial on howto-use tables to fully understand the rendering mechanism

http://download.oracle.com/javase/tutorial/uiswing/components/table.html

Roughly:

   // change the model, will notify its listeners
   model.setValueAt(....)

   // in a custom renderer, check the value and decorate as appropriate
   public Component getTableCellRendererComponent(....) {
        // ... normal config, f.i. done in super
        Component comp = super.get...
        if (myConditionForSpecialColor(table, value, ...) {
            comp.setBackground(myColor);
        } else {
            comp.setBackground(normalColor);
        }
   }

   // register the custom renderer 
   // per class
   table.setDefaultRenderer(Object.class, myRenderer)
   // or per column
   table.getColumnModel().getColumn(myColumn).setCellRenderer(myRenderer)