[[!meta title="Qt: Throw exceptions from signals and slots"]]
[[!meta date="2010-07-08"]]
[[!meta author="rohieb"]]
[[!meta license="CC-BY-SA 3.0"]]

By default, you can not throw exceptions from signals and slots, and if
you try it, you get the following message:

> Qt has caught an exception thrown from an event handler. Throwing
> exceptions from an event handler is not supported in Qt. You must
> reimplement QApplication::notify() and catch all exceptions there.

So, what to do? The answer is simple: Overwrite the function `bool
QApplication::notify(QObject * receiver, QEvent * event)` so that it
catches all thrown exceptions. Here is some sample code:

[[!format c """
#include <QtGui>
#include <QApplication>
class MyApplication : public QApplication {
public:
    MyApplication(int& argc, char ** argv) :
        QApplication(argc, argv) { }
    virtual ~MyApplication() { }

    // reimplemented from QApplication so we can throw exceptions in slots
    virtual bool notify(QObject * receiver, QEvent * event) {
        try {
            return QApplication::notify(receiver, event);
        } catch(std::exception& e) {
            qCritical() << "Exception thrown:" << e.what();
        }
        return false;
    }
};
int main(int argc, char* argv[]) {
    MyApplication app(argc, argv);
    // ...
}
"""]]

Of course, you can also inherit from `QCoreApplication` to get rid of
the `QtGui` dependency, or display a nice dialog box instead of printing
the messages to the console, or…

Found at: [Stack Overflow: Qt and error handling strategy][1]

[1]: http://stackoverflow.com/questions/1578331/qt-and-error-handling-strategy

[[!tag howto programming exceptions Qt signals slots]]