代码如下：
1 XXX::XXX(QWidget *parent /* = 0 */)
2 {
3 ..................
4 //注意，resize一定要放在这段代码的前面
5 resize(300, 300);
6 int cx, cy;
7 //当parent为空时，窗口就显示在桌面中央
8 if( NULL == parent )
9 {
10 cx = (QApplication::desktop()->width() - width()) / 2;
11 cy = (QApplication::desktop()->height() - height()) / 2;
12 }
13 //否则，控件就显示在父部件中央
14 else
15 {
16 cx = ( parent->width() - width() ) / 2;
17 cy = ( parent->height() - height() ) / 2;
18 }
19 move(cx, cy);
20 ....................
21 }
