QQuickWindow: don't leak old screenChanged connections

Connections could accumulate. Because the newest one was invoked
last due to how signal-slot invocations are ordered, rendering
was correct, but the stale connections caused unnecessary updates
(and wasted a small amount of memory).
This comes from a misunderstanding I had at the time about how
QMetaObject::Connection works. Destroying or overwriting one does
not affect the actual connection.

While at it, also modernize the connect().

Change-Id: Idde81bdbff8947ed517bf2740d623a395c0acb74
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>
(cherry picked from commit 9f8292d48913c5bc50377749c2b3e030cf16d703)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

1 files changed, 3 insertions, 4 deletions

diff --git a/src/quick/items/qquickwindow.cpp b/src/quick/items/qquickwindow.cpp
index d71e6ec1a5..85b59aa7ba 100644
--- a/src/quick/items/qquickwindow.cpp
+++ b/src/quick/items/qquickwindow.cpp
@@ -435,15 +435,14 @@ void QQuickWindow::physicalDpiChanged()
 void QQuickWindow::handleScreenChanged(QScreen *screen)
 {
     Q_D(QQuickWindow);
+    disconnect(d->physicalDpiChangedConnection);
     if (screen) {
         physicalDpiChanged();
         // When physical DPI changes on the same screen, either the resolution or the device pixel
         // ratio changed. We must check what it is. Device pixel ratio does not have its own
         // ...Changed() signal.
-        d->physicalDpiChangedConnection = connect(screen, SIGNAL(physicalDotsPerInchChanged(qreal)),
-                                                  this, SLOT(physicalDpiChanged()));
-    } else {
-        disconnect(d->physicalDpiChangedConnection);
+        d->physicalDpiChangedConnection = connect(screen, &QScreen::physicalDotsPerInchChanged,
+                                                  this, &QQuickWindow::physicalDpiChanged);
     }
 
     d->forcePolish();