Merge pull request #5992 from 3nids/fix17790

fix NULL constraint on date/time widget with allow NULL

python/gui/editorwidgets/qgsdatetimeedit.sip

@@ -12,6 +12,13 @@ class QgsDateTimeEdit : QDateTimeEdit
 {
 %Docstring
  The QgsDateTimeEdit class is a QDateTimeEdit with the capability of setting/reading null date/times.
+
+.. warning::
+
+   You should use the signal valueChanged of this subclass
+rather than QDateTimeEdit.dateTimeChanged. If you consequently connect parent's
+dateTimeChanged signal and call dateTime() afterwards there is no warranty to
+have a proper NULL value handling.
 %End
 
 %TypeHeaderCode
@@ -63,6 +70,14 @@ Set the current date as NULL
 Resets the widget to show no value (ie, an "unknown" state).
 
 .. versionadded:: 2.16
+%End
+
+  signals:
+
+    void valueChanged( const QDateTime &date );
+%Docstring
+signal emitted whenever the value changes.
+@param date the new date/time value.
 %End
 
   protected:

src/gui/editorwidgets/qgsdatetimeedit.cpp

@@ -62,7 +62,11 @@ void QgsDateTimeEdit::clear()
 
     changed( QDateTime() );
 
-    // avoid slot double activation
+    // emit signal of QDateTime::dateTimeChanged with an invalid date
+    // anyway, using parent's signal should be avoided
+    // If you consequently connect parent's dateTimeChanged signal
+    // and call dateTime() afterwards there is no warranty to
+    // have a proper NULL value handling
     disconnect( this, &QDateTimeEdit::dateTimeChanged, this, &QgsDateTimeEdit::changed );
     emit dateTimeChanged( QDateTime() );
     connect( this, &QDateTimeEdit::dateTimeChanged, this, &QgsDateTimeEdit::changed );
@@ -174,6 +178,8 @@ void QgsDateTimeEdit::changed( const QDateTime &dateTime )
   }
 
   mClearAction->setVisible( mAllowNull && !mIsNull );
+
+  emit QgsDateTimeEdit::valueChanged( dateTime );
 }
 
 void QgsDateTimeEdit::displayNull( bool updateCalendar )

src/gui/editorwidgets/qgsdatetimeedit.h

@@ -23,6 +23,11 @@
 /**
  * \ingroup gui
  * \brief The QgsDateTimeEdit class is a QDateTimeEdit with the capability of setting/reading null date/times.
+ *
+ * \warning You should use the signal valueChanged of this subclass
+ * rather than QDateTimeEdit::dateTimeChanged. If you consequently connect parent's
+ * dateTimeChanged signal and call dateTime() afterwards there is no warranty to
+ * have a proper NULL value handling.
  */
 class GUI_EXPORT QgsDateTimeEdit : public QDateTimeEdit
 {
@@ -62,6 +67,14 @@ class GUI_EXPORT QgsDateTimeEdit : public QDateTimeEdit
      */
     void setEmpty();
 
+  signals:
+
+    /**
+     * signal emitted whenever the value changes.
+     * @param date the new date/time value.
+     */
+    void valueChanged( const QDateTime &date );
+
   protected:
     void mousePressEvent( QMouseEvent *event ) override;
     void focusOutEvent( QFocusEvent *event ) override;

src/gui/editorwidgets/qgsdatetimeeditwrapper.cpp

@@ -93,7 +93,7 @@ void QgsDateTimeEditWrapper::initWidget( QWidget *editor )
 
   if ( mQgsDateTimeEdit )
   {
-    connect( mQgsDateTimeEdit, &QDateTimeEdit::dateTimeChanged, this, &QgsDateTimeEditWrapper::dateTimeChanged );
+    connect( mQgsDateTimeEdit, &QgsDateTimeEdit::valueChanged, this, &QgsDateTimeEditWrapper::dateTimeChanged );
   }
   else
   {