Qt Slot Signal

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I found out today that Qt’s slots/signals architecture is even better than I thought. Normally, developers connect widget signals to widget slots to be notified of events. Today I discovered that signals can actually be connected to other signals, which saved me from writing some really stupid code…

Slot

Cross thread calls - If you're making a signal-slot connection that needs to be cross thread then QT will automatically buffer the signals and queue them to the right thread. This happens automatically for instance when a GUI thread needs to communicate to a working thread. Here's more information in QT's documentation. The Signal class provides a way to declare and connect Qt signals in a pythonic way. PySide adopt PyQt’s new signal and slot syntax as-is. The PySide implementation is functionally compatible with the PyQt 4.5 one, with the exceptions listed bellow.

This may seem weird, but consider this scenario. You have a custom widget, called MyWidget, that has a signal, somethingClicked(), which is emitted when a user clicks, uh, something. But now you want to add a QPopupMenu as a right-click context menu, that causes the somethingClicked() signal to be emitted also. It turns out there’s a hard way and an easy way to do this.

First, the hard way:

1. Add a new slot called emitSomethingClickedSlot() that looks like this:

2. Then, connect the QPopupMenu‘s menu item to this slot, like so:

That sucks. We just created a slot whose sole purpose is to turn around and emit a signal. What a waste of editor space. It would have been smarter to connect the menu item’s signal directly to the somethingClicked() signal.

Here’s the easy way:

Now that’s concise. Sometimes it pays to connect signals to signals.

Signal

In this tutorial we will learn How to use signal and slots in qt.

File->New File or Project…

Applications->Qt Gui Application->Choose…

Python Qt Signal Slot

We keep the class as MainWindow as given by default.

SignalsAndSlots.pro

Qt signal slot parameter

Qt Signal Slot Between Classes

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#include <QApplication>
intmain(intargc,char*argv[])
QApplicationa(argc,argv);
w.show();
returna.exec();