= Handling context menus =

On the #pyqt channel on Freenode, `jams` asked about adding a context menu to a table widget.

The context menu policy described by [[http://www.riverbankcomputing.com/static/Docs/PyQt4/html/qt.html#ContextMenuPolicy-enum|Qt.ContextMenuPolicy]] determines how context menus are handled by each widget. To choose a policy, we call its [[http://www.riverbankcomputing.com/static/Docs/PyQt4/html/qwidget.html#setContextMenuPolicy|setContextMenuPolicy()]] method with one of the policy values. The useful policies are `DefaultContextMenu`, `ActionsContextMenu` and `CustomContextMenu`.

This means that there are basically three ways to add a context menu to a widget:

 1. Subclass the widget and reimplement its [[http://www.riverbankcomputing.com/static/Docs/PyQt4/html/qwidget.html#contextMenuEvent|contextMenuEvent()]] handler method, using the default context menu policy.
 2. Add actions to the widget and set the context menu policy to `ActionsContextMenu`.
 3. Set the context menu policy to `CustomContextMenu` and connect the widget's [[http://www.riverbankcomputing.com/static/Docs/PyQt4/html/qwidget.html#customContextMenuRequested|customContextMenuRequested()]] signal to a slot or method where a menu can be opened.

The code for the examples shown here can be found as attachments to this page:

 * [[attachment:custommenu_subclass.py]]
 * [[attachment:custommenu_actions.py]]
 * [[attachment:custommenu_actions_standard.py]]
 * [[attachment:custommenu_signal.py]]

== Subclassing ==

If you are writing a custom widget or are subclassing a standard widget, the default subclassing approach is quite convenient.

We reimplement the context menu event and create our own menu, making sure that we convert the position passed in the `event` object from local widget coordinates to global screen coordinates.

{{{
#!python
import sys
from PyQt4.QtCore import Qt
from PyQt4.QtGui import *

class TableWidget(QTableWidget):

    def __init__(self, parent = None):
    
        QTableWidget.__init__(self, parent)
    
    def contextMenuEvent(self, event):
    
        menu = QMenu(self)
        quitAction = menu.addAction("Quit")
        action = menu.exec_(self.mapToGlobal(event.pos()))
        if action == quitAction:
            qApp.quit()

app = QApplication([])
tableWidget = TableWidget()
tableWidget.show()
sys.exit(app.exec_())
}}}

== Actions ==

For widgets with built-in actions, we can change the policy to `ActionsContextMenu` and the widget will automatically obtain its own context menu. For widgets without built-in actions, we can add new ones.

{{{
#!python
import sys
from PyQt4.QtCore import Qt
from PyQt4.QtGui import *

class TableWidget(QTableWidget):

    def __init__(self, parent = None):
    
        QTableWidget.__init__(self, parent)
        self.setContextMenuPolicy(Qt.ActionsContextMenu)
        
        quitAction = QAction("Quit", self)
        quitAction.triggered.connect(qApp.quit)
        self.addAction(quitAction)

app = QApplication([])
tableWidget = TableWidget()
tableWidget.show()
sys.exit(app.exec_())
}}}

We can even add actions to standard widgets without having to subclass them:

{{{
#!python

import sys
from PyQt4.QtCore import Qt
from PyQt4.QtGui import *

app = QApplication([])
tableWidget = QTableWidget()
tableWidget.setContextMenuPolicy(Qt.ActionsContextMenu)

quitAction = QAction("Quit", None)
quitAction.triggered.connect(qApp.quit)
tableWidget.addAction(quitAction)

tableWidget.show()
sys.exit(app.exec_())
}}}

== Signal and Slot ==

Sometimes, when we do not want to subclass a standard widget or use actions, it is easier to handle the context menu in a separate component, so we need a way for the widget to notify us when a context menu has been requested. We can do this by changing the policy to `CustomContextMenu` and connecting the widget's `customContextMenuRequested()` signal to a slot, method or function.

{{{
#!python

import sys
from PyQt4.QtCore import Qt
from PyQt4.QtGui import *

app = QApplication([])
tableWidget = QTableWidget()
tableWidget.setContextMenuPolicy(Qt.CustomContextMenu)

def openMenu(position):

    menu = QMenu()
    quitAction = menu.addAction("Quit")
    action = menu.exec_(tableWidget.mapToGlobal(position))
    if action == quitAction:
        qApp.quit()

tableWidget.customContextMenuRequested.connect(openMenu)
tableWidget.show()
sys.exit(app.exec_())
}}}

The signal delivers a [[http://www.riverbankcomputing.com/static/Docs/PyQt4/html/qpoint.html|QPoint]] value, representing the position of the menu request in local widget coordinates. As before, we convert the position to a global screen position before showing the menu.