Signals و slots سیگنال ها و شکاف ها در PyQt. ویجت های PyQt به عنوان گیرنده ی رویداد عمل می کنند، یعنی هر ویجت می تواند تعداد خاصی از رویدادها را بگیرد؛ مثل کلیک ماوس، فشردن کلیدها و.
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- To establish a signal and slot connection between two widgets in a dialog, you first need to switch to Qt Designer's Edit Signals/Slots mode. To do that, you can press the F4 key, select the EditEdit Signals/Slots option in the main menu, or click on the Edit Signals/Slots button on the toolbar.
- Signals and slots is a language construct introduced also in Qt for communication between objects which makes it easy to implement the observer pattern while avoiding boilerplate code.
- Source Codes: PyQt5 Signal And Slots Basics Pyhton GUI Programming Graphical applications (GUI) are event-driven, unlike.
- Qt Designer can also be used to make signal-slot connections, but only between built-in signals and slots. Once a user interface has been designed and saved in a.ui file, it must be converted into code before it can be used.
- PyQt5 Tutorial
- PyQt5 Useful Resources
- Selected Reading
Unlike a console mode application, which is executed in a sequential manner, a GUI based application is event driven. Functions or methods are executed in response to user's actions like clicking on a button, selecting an item from a collection or a mouse click etc., called events.
Widgets used to build the GUI interface act as the source of such events. Each PyQt widget, which is derived from QObject class, is designed to emit ‘signal' in response to one or more events. The signal on its own does not perform any action. Instead, it is ‘connected' to a ‘slot'. The slot can be any callable Python function.
Using Qt Designer's Signal/Slot Editor
First design a simple form with a LineEdit control and a PushButton.
It is desired that if button is pressed, contents of text box should be erased. The QLineEdit widget has a clear() method for this purpose. Hence, the button's clicked signal is to be connected to clear() method of the text box.
To start with, choose Edit signals/slots from Edit menu (or press F4). Then highlight the button with mouse and drag the cursor towards the textbox
As the mouse is released, a dialog showing signals of button and methods of slot will be displayed. Select clicked signal and clear() method
The Signal/Slot Editor window at bottom right will show the result −
Save ui and Build and Python code from ui file as shown in the below code −
Generated Python code will have the connection between signal and slot by the following statement −
Run signalslot.py and enter some text in the LineEdit. The text will be cleared if the button is pressed.
Building Signal-slot Connection
Instead of using Designer, you can directly establish signal-slot connection by following syntax −
Suppose if a function is to be called when a button is clicked. Here, the clicked signal is to be connected to a callable function. It can be achieved in any of the following technique −
Example
In the following example, two QPushButton objects (b1 and b2) are added in QDialog window. We want to call functions b1_clicked() and b2_clicked() on clicking b1 and b2 respectively.
When b1 is clicked, the clicked() signal is connected to b1_clicked() function −
When b2 is clicked, the clicked() signal is connected to b2_clicked() function.
The above code produces the following output − Romantic resorts in atlanta ga.
Output
Qt Designer is the Qt tool for designing and building graphical userinterfaces. It allows you to design widgets, dialogs or complete main windowsusing on-screen forms and a simple drag-and-drop interface. It has the abilityto preview your designs to ensure they work as you intended, and to allow youto prototype them with your users, before you have to write any code.
Qt Designer uses XML .ui files to store designs and does not generate anycode itself. Qt includes the uic utility that generates the C++ code thatcreates the user interface. Qt also includes the QUiLoader class thatallows an application to load a .ui file and to create the correspondinguser interface dynamically.
PyQt does not wrap the QUiLoader class but instead includes theuic Python module. Like QUiLoader this module can load.ui files to create a user interface dynamically. Like the uicutility it can also generate the Python code that will create the userinterface. PyQt's pyuic4 utility is a command line interface to theuic module. Both are described in detail in the followingsections.
Using the Generated Code¶
The code that is generated has an identical structure to that generated by Qt'suic and can be used in the same way.
The code is structured as a single class that is derived from the Pythonobject type. The name of the class is the name of the toplevel object setin Designer with Ui_ prepended. (In the C++ version the class is definedin the Ui namespace.) We refer to this class as the form class.
The class contains a method called setupUi(). This takes a single argumentwhich is the widget in which the user interface is created. The type of thisargument (typically QDialog, QWidget or QMainWindow) is set inDesigner. We refer to this type as the Qt base class.
In the following examples we assume that a .ui file has been createdcontaining a dialog and the name of the QDialog object is ImageDialog.We also assume that the name of the file containing the generated Python codeis ui_imagedialog.py. The generated code can then be used in a numberof ways.
The first example shows the direct approach where we simply create a simpleapplication to create the dialog:
The second example shows the single inheritance approach where we sub-classQDialog and set up the user interface in the __init__() method:
The third example shows the multiple inheritance approach:
It is also possible to use the same approach used in PyQt v3. This is shown inthe final example:
For a full description see the Qt Designer Manual in the Qt Documentation.
The uic Module¶
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The uic module contains the following functions and objects.
Unlike a console mode application, which is executed in a sequential manner, a GUI based application is event driven. Functions or methods are executed in response to user's actions like clicking on a button, selecting an item from a collection or a mouse click etc., called events.
Widgets used to build the GUI interface act as the source of such events. Each PyQt widget, which is derived from QObject class, is designed to emit ‘signal' in response to one or more events. The signal on its own does not perform any action. Instead, it is ‘connected' to a ‘slot'. The slot can be any callable Python function.
Using Qt Designer's Signal/Slot Editor
First design a simple form with a LineEdit control and a PushButton.
It is desired that if button is pressed, contents of text box should be erased. The QLineEdit widget has a clear() method for this purpose. Hence, the button's clicked signal is to be connected to clear() method of the text box.
To start with, choose Edit signals/slots from Edit menu (or press F4). Then highlight the button with mouse and drag the cursor towards the textbox
As the mouse is released, a dialog showing signals of button and methods of slot will be displayed. Select clicked signal and clear() method
The Signal/Slot Editor window at bottom right will show the result −
Save ui and Build and Python code from ui file as shown in the below code −
Generated Python code will have the connection between signal and slot by the following statement −
Run signalslot.py and enter some text in the LineEdit. The text will be cleared if the button is pressed.
Building Signal-slot Connection
Instead of using Designer, you can directly establish signal-slot connection by following syntax −
Suppose if a function is to be called when a button is clicked. Here, the clicked signal is to be connected to a callable function. It can be achieved in any of the following technique −
Example
In the following example, two QPushButton objects (b1 and b2) are added in QDialog window. We want to call functions b1_clicked() and b2_clicked() on clicking b1 and b2 respectively.
When b1 is clicked, the clicked() signal is connected to b1_clicked() function −
When b2 is clicked, the clicked() signal is connected to b2_clicked() function.
The above code produces the following output − Romantic resorts in atlanta ga.
Output
Qt Designer is the Qt tool for designing and building graphical userinterfaces. It allows you to design widgets, dialogs or complete main windowsusing on-screen forms and a simple drag-and-drop interface. It has the abilityto preview your designs to ensure they work as you intended, and to allow youto prototype them with your users, before you have to write any code.
Qt Designer uses XML .ui files to store designs and does not generate anycode itself. Qt includes the uic utility that generates the C++ code thatcreates the user interface. Qt also includes the QUiLoader class thatallows an application to load a .ui file and to create the correspondinguser interface dynamically.
PyQt does not wrap the QUiLoader class but instead includes theuic Python module. Like QUiLoader this module can load.ui files to create a user interface dynamically. Like the uicutility it can also generate the Python code that will create the userinterface. PyQt's pyuic4 utility is a command line interface to theuic module. Both are described in detail in the followingsections.
Using the Generated Code¶
The code that is generated has an identical structure to that generated by Qt'suic and can be used in the same way.
The code is structured as a single class that is derived from the Pythonobject type. The name of the class is the name of the toplevel object setin Designer with Ui_ prepended. (In the C++ version the class is definedin the Ui namespace.) We refer to this class as the form class.
The class contains a method called setupUi(). This takes a single argumentwhich is the widget in which the user interface is created. The type of thisargument (typically QDialog, QWidget or QMainWindow) is set inDesigner. We refer to this type as the Qt base class.
In the following examples we assume that a .ui file has been createdcontaining a dialog and the name of the QDialog object is ImageDialog.We also assume that the name of the file containing the generated Python codeis ui_imagedialog.py. The generated code can then be used in a numberof ways.
The first example shows the direct approach where we simply create a simpleapplication to create the dialog:
The second example shows the single inheritance approach where we sub-classQDialog and set up the user interface in the __init__() method:
The third example shows the multiple inheritance approach:
It is also possible to use the same approach used in PyQt v3. This is shown inthe final example:
For a full description see the Qt Designer Manual in the Qt Documentation.
The uic Module¶
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The uic module contains the following functions and objects.
The list of the directories that are searched for widget plugins.Initially it contains the name of the directory that contains the widgetplugins included with PyQt.
Generate a Python module that will create a user interface from a QtDesigner .ui file.
| Parameters: |
|
|---|
Create Python modules from Qt Designer .ui files in a directory ordirectory tree.
| Parameters: |
|
|---|
Load a Qt Designer .ui file and return a tuple of the generatedform class and the Qt base class. These can then be used tocreate any number of instances of the user interface without having toparse the .ui file more than once.
| Parameters: |
|
|---|---|
| Return type: | the form class and the Qt base class. |
Load a Qt Designer .ui file and returns an instance of the userinterface.
| Parameters: |
|
|---|---|
| Return type: | the QWidget sub-class that implements the user interface. |
pyuic4¶
The pyuic4 utility is a command line interface to theuic module. The command has the following syntax:
The full set of command line options is:
A help message is written to stdout.
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The version number is written to stdout.
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The Python code is generated using an indentation of spaces. If is 0 then a tab is used. The default is 4.
The Python code generated is written to the file .
The GUI is created dynamically and displayed. No Python code is generated.
The generated Python code includes a small wrapper that allows the GUI tobe used in the same way as it is used in PyQt v3.
The generated Python code includes a small amount of additional code thatcreates and displays the GUI when it is executes as a standaloneapplication.
Resource modules are imported using from.import rather than a simpleimport.
Note that code generated by pyuic4 is not guaranteed to becompatible with earlier versions of PyQt. However, it is guaranteed to becompatible with later versions. If you have no control over the version ofPyQt the users of your application are using then you should runpyuic4, or call compileUi(), as part of yourinstallation process. Another alternative would be to distribute the .uifiles (perhaps as part of a resource file) and have your application load themdynamically.
Writing Qt Designer Plugins¶
Qt Designer can be extended by writing plugins. Normally this is done usingC++ but PyQt also allows you to write plugins in Python. Most of the time aplugin is used to expose a custom widget to Designer so that it appears inDesigner's widget box just like any other widget. It is possibe to change thewidget's properties and to connect its signals and slots.
It is also possible to add new functionality to Designer. See the Qtdocumentation for the full details. Here we will concentrate on describinghow to write custom widgets in Python.
The process of integrating Python custom widgets with Designer is very similarto that used with widget written using C++. However, there are particularissues that have to be addressed.
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- Designer needs to have a C++ plugin that conforms to the interface defined bythe QDesignerCustomWidgetInterface class. (If the plugin exposes morethan one custom widget then it must conform to the interface defined by theQDesignerCustomWidgetCollectionInterface class.) In addition the pluginclass must sub-class QObject as well as the interface class. PyQt doesnot allow Python classes to be sub-classed from more than one Qt class.
- Designer can only connect Qt signals and slots. It has no understanding ofPython signals or callables.
- Designer can only edit Qt properties that represent C++ types. It has nounderstanding of Python attributes or Python types.
PyQt provides the following components and features to resolve these issues assimply as possible.
PyQt's QtDesigner module includes additional classes (all of which have aQPy prefix) that are already sub-classed from the necessary Qt classes.This avoids the need to sub-class from more than one Qt class in Python. Forexample, where a C++ custom widget plugin would sub-class from QObjectand QDesignerCustomWidgetInterface, a Python custom widget plugin wouldinstead sub-class from QPyDesignerCustomWidgetPlugin.
PyQt installs a C++ plugin in Designer's plugin directory. It conforms tothe interface defined by the QDesignerCustomWidgetCollectionInterfaceclass. It searches a configurable set of directories looking for Pythonplugins that implement a class sub-classed fromQPyDesignerCustomWidgetPlugin. Each class that is found is instantiatedand the instance created is added to the custom widget collection.
The PYQTDESIGNERPATH environment variable specifies the set ofdirectories to search for plugins. Directory names are separated by a pathseparator (a semi-colon on Windows and a colon on other platforms). If adirectory name is empty (ie. there are consecutive path separators or aleading or trailing path separator) then a set of default directories isautomatically inserted at that point. The default directories are thepython subdirectory of each directory that Designer searches for itsown plugins. If the environment variable is not set then only the defaultdirectories are searched. If a file's basename does not end with pluginthen it is ignored.
A Python custom widget may define new Qt signals usingpyqtSignal().
A Python method may be defined as a new Qt slot by using thepyqtSlot() decorator.
A new Qt property may be defined using the pyqtProperty()function.
Note that the ability to define new Qt signals, slots and properties fromPython is potentially useful to plugins conforming to any plugin interface andnot just that used by Designer.
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For a simple but complete and fully documented example of a custom widget thatdefines new Qt signals, slots and properties, and its plugin, look in theexamples/designer/plugins directory of the PyQt source package. Thewidgets subdirectory contains the pydemo.py custom widget andthe python subdirectory contains its pydemoplugin.py plugin.
