Fix main window turns blank after restoring from tray (qbittorrent#15031

)

When restoring from tray icon, although the window manager shows qbt
window but qbt itself didn't handle the event correctly, i.e. the
`show()` was missing and thus qbt did nothing and the window is blank.
Note that at this point the `visible` property is `false`.
After invoking `show()` qbt will start showing the contents and also
fire another showEvent where `visible` property is `true` and here is where
qbt should handle preparations for the window.

Fix qbittorrent#9510.

src/gui/mainwindow.cpp

@@ -1131,17 +1131,26 @@ void MainWindow::on_actionStatistics_triggered()
 void MainWindow::showEvent(QShowEvent *e)
 {
  qDebug("** Show Event **");
+ e->accept();
 
- if (currentTabWidget() == m_transferListWidget)
- m_propertiesWidget->loadDynamicData();
+ if (isVisible())
+ {
+ // preparations before showing the window
 
- e->accept();
+ if (currentTabWidget() == m_transferListWidget)
+ m_propertiesWidget->loadDynamicData();
 
- // Make sure the window is initially centered
- if (!m_posInitialized)
+ // Make sure the window is initially centered
+ if (!m_posInitialized)
+ {
+ move(Utils::Gui::screenCenter(this));
+ m_posInitialized = true;
+ }
+ }
+ else
  {
- move(Utils::Gui::screenCenter(this));
- m_posInitialized = true;
+ // to avoid blank screen when restoring from tray icon
+ show();
  }
 }