Qt Slot Not Being Called

• Qt Slot Not Getting Called
• Qt Slot Not Being Called Like

Qt Development General and Desktop. Signal not being called during unit test Important. Is called it never goes into the OnTimeout slot. Is the WaitCondition in.

Describe the pull request:

• [ x] Bug fix
• [ ] Functional change
• [ ] New feature
• [ ] Code cleanup
• [ ] Build system change
• [ ] Documentation change
• [ ] Language translation

Pull request long description:

It’s a fair question to ask, especially when the signal is coming from Qt itself or from a third-party library we have no control over. If the signal is not getting emitted, obviously the slot will never be called. Overriding/Reimplementing Slots in PySide. You cannot override QLineEdit.copy or QLineEdit.paste in such a way that they will be called internally by Qt. In general, you can only usefully override or reimplement Qt functions that are defined as being virtual. The Qt Docs will always specify whether this. I have a QTimer in MainWindow class but the update slot doesn't get called. I have no idea what it would be. Connect return true and I get neither warning from messages window in QT creator nor run-time errors. It just doesn't work. This method is also a Qt slot with the C signature void currentChanged(const QModelIndex&,const QModelIndex&). This slot is called when a new item becomes the current item. The previous current item is specified by the previous index, and the new item by the current index. If you want to know about changes to items see the dataChanged signal.

This PR solves a problem of missing signal/slots from QMLInterface. With the connect() being in the constructor that constructs a global object, there are no guarantee that the referenced objects are constructed, and thus sometimes leads to the connect not being successful. Unfortunate Qt does not report an error when this happens.

Solution was to move the connect() back into setup(), while keeping the nice lambda changes.

Qt Slot Not Getting Called

In contrary to what I wrote earlier, we (a student who writes a paper on clang and myself) have, out of scientific interest, examined the clang compiler (Xcode 11.3.1) compiling for iOS, other compilers might behave differently.

We found that the global space is created in 3 steps:1) all public const (we are still debating if a class const is added at this step, it seems to depend on compiler switches). These are created in a special const segment, and are created by the linker.2) all public global variables, including classes. The sequence seems very random, changing the compile order is no guarantee of changing the sequence of constructor calls. Linker allocates the global space needed, and the constructors are called as part of the startup code.3) all private static variables, including those hidden in e.g. instance(). Because instance()does: static *self = new ; return self;

self is a hidden (compiler scope is local) global object, and it is constructed before instance() is called. We have seen hints that some optimization switches might cause a delayed construct, but for debug it is constructed as part of the global space creation.4) main is called

Based on these finding, it seems like a good idea, never to reference parallel global objects in a global constructor (actually this is also taught here in the C++ class).

Some of the reasons why this has not been detected before can be:1) most of the connects relate to the UI, and a missing change in a single graphical element is easily overlooked2) There are very little formal testing of the signal/slot (apart from qPref)3) Bulk of the connects are in desktop-widget, that connect a library (like e.g. core or backend-shared) to the UI, while QMLInterface interconnect signals.

remark, this was a practical study using Xcode 11.3.1 and IPadOS 13.1 simulator. I am sure reading the C++ specs contains some descriptions as well, but theory and practice are often two different pair of shoes.

Any positive comment and/or suggestions are mostly welcome.

Changes made:

Related issues:

Additional information:

Release note:

Documentation change:

Mentions:

该提问来源于开源项目：subsurface/subsurface

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Qt Slot Not Being Called Like

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