problem with replacing a background image using signal / slot in qt - qt

Question

i want to make a simple chess program. So far i've made the board using QTableWidget and loaded the piece pictures in the cells of table. Now i wnat to use signal and slot so that when user clicks a cell and then click another cell the piece picture from first cell goes to second cell, But I don't know how to do it.
Note that i don't want these "piece moves" obey the real chess rules. I only wnat to do the picture replacement between two cells . Later i will make them obey the rules.
here is the code. in this code only table's item(0,0) has a picture. can anyone say how to write a code so that when i click that item then click to item(1,1) , picture "1.bmp" goes to background of item(1,1)?
#include <QtGui/QApplication>
#include "mainwindow.h"
#include <QHBoxLayout>
#include <QTableWidget>
#include <QHeaderView>
class Table : public QWidget
{
Q_OBJECT
public:
Table(QWidget *parent = 0);
slots:
//??????
};
Table::Table(QWidget *parent)
: QWidget(parent)
{
QHBoxLayout *hbox = new QHBoxLayout(this);
QTableWidget *table = new QTableWidget(8 , 8 , this);
table->setFixedSize(900,900);
table->horizontalHeader()->setDefaultSectionSize(100);
table->verticalHeader()->setDefaultSectionSize(100);
table->horizontalHeader()->setResizeMode(QHeaderView::Fixed);
table->verticalHeader()->setResizeMode(QHeaderView::Fixed);
QString fileName = "/1.bmp";
QPixmap pic(fileName);
QBrush brush(pic);
QTableWidgetItem* item = new QTableWidgetItem();
item->setBackground(brush);
table->setItem(0,0,item);
hbox->addWidget(table);
setLayout(hbox);
}
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
Table table;
table.show();
return app.exec();
}

Answer 1

There are really two questions here.
The first one regarding signals/slots with QTableWidgetItem, and the second regarding handling mouse clicks on the QTableWidget.
Signals Slots on a QTableWidgetItem
note: I don't recommend doing it this way, read all the way to the bottom*
Using signals and slots requires that the object that emits the signal, have the signal defined in the class definition. Likewise the object that receives a slot, must have that slot declared in the class definition.
You'll notice (on the Qt docs) that QTableWidgetItem doesn't have a signals or slots to set/remove the background brush you are using to draw your picture. So, you will have to subclass QTableWidgetItem, and provide this signals/slots yourself.
Example:
class ChessItem : public QTableWidgetItem
{
// constructor / destructor
// other methods
public slots:
void slotChangeBackground( const QBrush & brush )
{
setBackground( brush );
}
};
Handling Mouse Clicks on the QTableWidget
edit: I removed the event handling paragraph, because using QTableWidget's builtin signals is easier
QTableWidget offers the cell clicked signal:
void QTableWidget::cellClicked ( int row, int column )
So in your Table class add a slot, then connect it the cellClicked signal to it:
// in your Table's constructor:
connect( table, SIGNAL( cellClicked(int, int) ), this, SLOT( slotCellClicked(int,int) ) ) );
// elsewhere...
void slotCellClicked(int row, int column) {
// handle mouse clicking here
}
The problem as I see it is you don't want to just connect any ol signal to slotChangeBackground, because that would change every background. So I suggest not using signals/slots for changing the background, and instead use QTableWidget::itemAt ( int ax, int ay ) in your slotCellClicked(x,y) to retrieve the item at a coordinate, then call setBackground on it.