iOS: Ensure UIApplicationMain is started before QApplication by wrapping main()

For the typical Qt app the developer will have an existing main() that
looks something like:

int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);

    return app.exec();
}

To support this, we provide our own 'main' function in the
qtmain static library that we link into the application, which calls
UIApplicationMain and redirects to the 'main' function of the application
after the event loop has started spinning. For this to work, the applications
'main' function needs to manually be renamed 'qt_main' for now. In a later
patch, this renaming will happen automatically by redefining main from either a
header file, or more likely, from the Makefile created by qmake.

For the case of an iOS developer wanting to use Qt in their existing app
the main will look something like:

int main(int argc, char *argv[])
{
    @autoreleasepool {
        return UIApplicationMain(argc, argv, nil, NSStringFromClass([AppDelegate class]));
    }
}

This is supported right now by just linking in libqios.a without libqiosmain.a.
QGuiApplication should then be created e.g inside the native apps application
delegate (but QGuiApplication::exec should not be called).

In the future, we plan to but use a wrapper library that
brings in all the Qt dependencies into one single static library. This library will
not link against qtmain, so there won't be a symbol clash if the -ObjC linker option
is used. We should then add the required magic to the future Objective-C convenience
wrapper for QML to bring up a QGuiApplication, which would allow using Qt from
storyboards and NIBs. This would also be the place to inject our own
application delegate into the mix, while proxying the delegate callbacks
to the user's application delegate.

Change-Id: Iba5ade114b27216be8285f36100fd735a08b9d59
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@digia.com>
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@digia.com>

1 files changed, 2 insertions, 12 deletions

diff --git a/src/plugins/platforms/ios/qioseventdispatcher.mm b/src/plugins/platforms/ios/qioseventdispatcher.mm
index 252e375a54..9d455370c0 100644
--- a/src/plugins/platforms/ios/qioseventdispatcher.mm
+++ b/src/plugins/platforms/ios/qioseventdispatcher.mm
@@ -191,23 +191,13 @@ bool QIOSEventDispatcher::processEvents(QEventLoop::ProcessEventsFlags flags)
     m_interrupted = false;
     bool eventsProcessed = false;
 
-    UIApplication *uiApplication = [UIApplication sharedApplication];
     bool excludeUserEvents = flags & QEventLoop::ExcludeUserInputEvents;
     bool execFlagSet = (flags & QEventLoop::DialogExec) || (flags & QEventLoop::EventLoopExec);
     bool useExecMode = execFlagSet && !excludeUserEvents;
 
     if (useExecMode) {
-        if (!uiApplication) {
-            // No UIApplication has been started yet. We therefore start it now. Note that application
-            // developers are free to call UIApplicationMain themselves instead of QApplication::exec()
-            @autoreleasepool {
-                QCoreApplicationPrivate *qAppPriv = static_cast<QCoreApplicationPrivate *>(QObjectPrivate::get(qApp));
-                return UIApplicationMain(qAppPriv->argc, qAppPriv->argv, nil, NSStringFromClass([QIOSApplicationDelegate class]));
-            }
-        } else {
-            NSRunLoop *runLoop = [NSRunLoop currentRunLoop];
-            while ([runLoop runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]] && !m_interrupted);
-        }
+        NSRunLoop *runLoop = [NSRunLoop currentRunLoop];
+        while ([runLoop runMode:NSDefaultRunLoopMode beforeDate:[NSDate distantFuture]] && !m_interrupted);
         eventsProcessed = true;
     } else {
         if (!(flags & QEventLoop::WaitForMoreEvents))