QT C++ 5 Signal and Slots part 1 mp4
Introduction In some applications it is often necessary to perform long-running tasks, such as computations or network operations, that cannot be broken up into smaller pieces and processed alongside normal application events.
In such cases, we would like to be able to perform these tasks in a way that does not interfere with the normal running of the application, and ensure that the user interface continues to be updated.
One way of achieving this is to perform these tasks in a separate thread to the main user interface thread, and only interact with it when we have results we need to display.
This example shows how to create a separate thread to perform a task - in this case, drawing stars for a picture - while continuing to run the main user interface thread.
The worker thread draws each star onto its own individual image, and it passes each image back to the example's window which resides in the main application thread.
The User Interface We begin by importing the modules we require.
We need the math and random modules to help us draw stars.
We create a single Worker instance that we can reuse as required.
The user free video slots sevens las vegas consists of read article label, spin box and a push button that the user interacts with to configure the number of stars that the thread wil draw.
The output from the thread is presented in a QLabel instance, viewer.
This will reset the user interface when the thread stops running.
The custom output QRect, QImage signal is connected to the addImage slot so that we can update the viewer label every time a new star is drawn.
Since the start button is the only widget that can cause this slot to be invoked, we simply disable it before starting the thread, avoiding problems with re-entrancy.
Whenever is star is drawn by qwidget signals and slots worker thread, it will emit a signal that is connected to the addImage slot.
The updateUi slot is called when a thread stops running.
Since we usually want to let the user run the thread again, free video slots sevens las vegas reset the user interface to enable the start button to be pressed: def updateUi go here : self.
The Worker Thread The worker thread is implemented as a thread rather than a Python thread since we want to take advantage of the signals and slots mechanism to communicate qwidget signals and slots the main application.
The exiting attribute is used to tell the thread to stop processing.
Each star is drawn using a QPainterPath that we define in advance: self.
For this reason, we implement the following method in a way that indicates to the part of the object that performs the processing that it must stop, and waits until it does so.
We provide the render method instead of letting our own run method take extra arguments because the run method is called by itself with no arguments.
The run method is where we perform the processing that occurs in the thread provided by the Worker instance: def run self : Note: This is never called directly.
It is called by Qt once the thread environment has been set up.
We draw the number of stars requested as long as the exiting attribute remains False.
This additional check allows us to terminate the thread on demand by setting the exiting attribute to True free video slots sevens las vegas any time.
We simply draw on an appropriately-sized transparent image.
For each star drawn, we send the main thread information about where it should be placed along with the star's image by emitting our custom output signal: self.
Qt Creator & C++ - SIGNAL+SLOT+Eventos - Video 2 - QWidget QMainwindow
Sending Python values with signals and slots. On the #pyqt channel on Freenode, Khertan asked about sending Python values via Qt's signals and slots mechanism.. The following example uses the PyQt_PyObject value declaration with an old-style signal-slot connection, and again when the signal is emitted, to communicate a Python dictionary.
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