use QMainWindow.closeEvent for close events

tecki · tecki · commit e4079268e9e0 · 2012-11-14T12:19:10.000+01:00
The current code uses the QWidget.destroyed signal
to emit a close event into matplotlib. This is a very
bad idea, as it is a heavy abuse of Qt functionality.

When a main window is closed in Qt, it and its children
are deleted if the DeleteOnClose flag is set (which we
did set). This causes the QWidget.destroyed signal to be
called. Setting the DeleteOnClose flag is a very bad
idea, since objects should only be deleted by the
garbage collector. Soon after, PyQt4 will complain
that "the underlying C++ object has been deleted", since
the object is alive for python but dead for C++.

This patch changes the machinery to use the
QMainWindow.closeEvent to emit a close_event, which is
what one actually wants.
diff --git a/lib/matplotlib/backends/backend_qt4.py b/lib/matplotlib/backends/backend_qt4.py
@@ -208,18 +208,6 @@ def __init__( self, figure ):
         w,h = self.get_width_height()
         self.resize( w, h )
 
-        # JDH: Note the commented out code below does not work as
-        # expected, because according to Pierre Raybaut, The reason is
-        # that PyQt fails (silently) to call a method of this object
-        # just before detroying it. Using a lambda function will work,
-        # exactly the same as using a function (which is not bound to
-        # the object to be destroyed).
-        #
-        #QtCore.QObject.connect(self, QtCore.SIGNAL('destroyed()'),
-        #    self.close_event)
-        QtCore.QObject.connect(self, QtCore.SIGNAL('destroyed()'),
-                               lambda: self.close_event())
-
     def __timerEvent(self, event):
         # hide until we can test and fix
         self.mpl_idle_event(event)
@@ -377,6 +365,10 @@ def idle_draw(*args):
             self._idle = True
         if d: QtCore.QTimer.singleShot(0, idle_draw)
 
+class MainWindow(QtGui.QMainWindow):
+    def closeEvent(self, event):
+        self.emit(QtCore.SIGNAL('closing()'))
+
 class FigureManagerQT( FigureManagerBase ):
     """
     Public attributes
@@ -391,8 +383,9 @@ def __init__( self, canvas, num ):
         if DEBUG: print('FigureManagerQT.%s' % fn_name())
         FigureManagerBase.__init__( self, canvas, num )
         self.canvas = canvas
-        self.window = QtGui.QMainWindow()
-        self.window.setAttribute(QtCore.Qt.WA_DeleteOnClose)
+        self.window = MainWindow()
+        self.window.connect(self.window, QtCore.SIGNAL('closing()'),
+            canvas.close_event)
 
         self.window.setWindowTitle("Figure %d" % num)
         image = os.path.join( matplotlib.rcParams['datapath'],'images','matplotlib.png' )
@@ -619,7 +612,6 @@ def draw_rubberband( self, event, x0, y0, x1, y1 ):
     def configure_subplots(self):
         self.adj_window = QtGui.QMainWindow()
         win = self.adj_window
-        win.setAttribute(QtCore.Qt.WA_DeleteOnClose)
 
         win.setWindowTitle("Subplot Configuration Tool")
         image = os.path.join( matplotlib.rcParams['datapath'],'images','matplotlib.png' )
