Thread: JTable custom model listener

Originally Posted by Bebras

I created a default JTable and added a listener to it. Everything worked great. But the default model wasn't good enought

First, just for clarity: you are speaking about a "listener". A table model is not a listener.
It depends on what table model you have used. If you have used the constructor JTable(Object[][] rowData, Object[] columnNames), it uses an implicit-internal table model. But there is also the class DefaultTableModel.

Originally Posted by Bebras

so I created my own.

Conceptually, your table model is not much better than the implicit table model into JTable or the DefaultTableModel. Your table model is still "generical" and unstructured, without any notion of the "entity" represented by each row.

The only "new" thing is that now, being developed by you, the table model can control the editability of cells.

Originally Posted by Bebras

And once I change data nothing happens.

Your table model is quite correct. It "exposes" all the informations in the right way. But the setValueAt is not completely correct. It's necessary to change the internal data structure (obviously) but not sufficient. You have to "fire" the appropriate event so that JTable (and any other registered TableModelListener) can known that "something" is changed (for JTable it means: update the view).

So, in setValueAt use also the fireTableCellUpdated(int row, int column) to send this notification.

I would recommend extending DefaultTableModel, not AbstractTableModel. The reason being is that DefaultTableModel would have existing functionality which you may have overlooked. It is more of a simplification technique than a requirement. Extending AbstractTableModel should be fine. I'm just giving my two cents.

Are you changing data by editing the table directly? If so, I don't know if the model data is changed by default. You might need to add a listener to the table and manually trigger the update or something.

Originally Posted by Bebras

But this code does not work. Nothing is "editable" meaning I can't click the button.(100% the index is correct), but if i always return true, then it works(but other cells ar editable, which is something i don't want)

A false from isCellEditable means primarily one thing: that the table cell editor never become "active".

So you want button column editable and all other columns non-editable, right? And then your last code is .... conceptually correct!

Originally Posted by Bebras

Yes that is right. Why do you say "conceptually"? How it isn't correct?

The concept "if it's the buttons column, return true otherwise return false" is correct. But technically, is 7 the column index of buttons? Are you sure?

Originally Posted by Bebras

Just to be sure.

Yes, for what I see it's the eighth column, that is index 7 (being 0-based). And what happens? Is the button clickable or not?

P.S. do you have hidden/zero-width columns?

Just as an exercise in testing andbin's theory, tell me if this changes the result:

@Override 
	public boolean isCellEditable(int rowIndex,int columnIndex) {
		if(columnIndex == getColumnCount()-1) return true;
		return false;
	}

In the final code, you would probably want hardcoded column numbers (unless you intend the last column to always be the button, I suppose, but hardcoded for this scenario would probably be best since it would reduce complexity).

Ok. Wait, so if you set the table to be fully editable, are you 100% the button works?

With your current setup (with only column 7 enabled), add this to the end of your code:

System.out.println(list.isCellEditable(0,7)+"");
System.out.println(list.getModel().isCellEditable(0,7)+"");

And tell us what the results are.

Originally Posted by Bebras

		TableColumn col = new TableColumn();
		col.setCellRenderer(button);
		col.setCellEditor(button);
		col.setHeaderValue("Veiksmas");
		list.addColumn(col);

Wait! You are adding an explicit column! And a TableColumn has the 'modelIndex' property (getModelIndex/setModelIndex methods) that you have not configured, thus it's 0. In other words: when isCellEditable is invoked for the added column, the column parameter is 0.

Originally Posted by Bebras

and got an array index out of bounds exception.

Where? I suspect in the getValueAt of your BanListTableModel.
Describe (or post) your BanListTableModel.

Originally Posted by Bebras

Should I just check if it is a valid index? But somehow that doesn't sound correct. What value does it have to return for a button?

The value from getValueAt is, at the end, simply passed to the renderer. If your button-renderer doesn't care about the value, you can return null, "", anything you want.

Imagine another scenario, for example, where you want to have different texts for each button. Here you would need a button-renderer that cares about the value, and set it to the button. And all texts would be "exposed" by the table model.

Originally Posted by Bebras

Your scenario sounds great and I'm pretty sure I'll want to add more buttons with different texts. So following this scenario I should keep the button text stored(a private instance variable) and return that ?

The first important thing is that your getValueAt must return the button text when requested for the row/column of a button. How you decide what text to return is a "strategy" that involves only the internal logic of the table model. You can have the text stored in the data array, or it can be decided basing on other values or other logic. All this is not important from an external point of view.

The renderer receives the value as a parameter to the getTableCellRendererComponent method as an Object. You "know" that this object is a String, being for a button text. So every time you prepare the component (your button) to return, simply set also the text.
Note that typically (to save on resources) the renderer is itself the component to return. So typically the returned component is always the same object, just prepared from time to time.

For the editor is a similar story (see getTableCellEditorComponent of TableCellEditor).

Originally Posted by Bebras

These "strategies" you were talking about ? Can you give me an example? Now I just set the button's text to the same text as text in data array.

I mean, in general, that it's not always necessary to keep an entire column in the internal data structure of the model for these button texts. Imagine a table model for stock prices, where the internal data structure has some informations that you can use to deduce if the button text must be "Sell" or "Buy".
Something like this ...

The choice of the text can also be delegated to the renderer/editor. The table model could return an int or enum value and the renderer/editor can select the appropriate text. These are design choices, that doesn't change the final result.

The important thing is that there must be an implicit "relation" between the renderer/editor and the value of the relative column in the model.