ENH: Make PyDMDrawingPolyline easier to use

-Add update button, saves and applies changes to settings
without closing the settings-editor window
-Add ability to swap point ordering in settings-editor
by drag and drop

pydm/widgets/designer_settings.py

@@ -110,6 +110,28 @@ def __init__(self, values=None, *args, parent=None, **kwargs):
         self.customContextMenuRequested.connect(self._context_menu)
         self.values
 
+        #we let user swap points by dragging one on-top of the other
+        self.setDragEnabled(True)
+        self.setAcceptDrops(True)
+        self.drag_source_row = None
+
+    def startDrag(self, event):
+        self.drag_source_row = self.currentRow()
+        #call super() since we use the default dragging functionality
+        super().startDrag(event)
+
+    def dropEvent(self, event):
+        source_row = self.drag_source_row
+        target_row = self.indexAt(event.pos()).row()
+        if target_row >= 0 and source_row != target_row:
+            self.swap_rows(source_row, target_row)
+
+    def swap_rows(self, row1, row2):
+        item1 = self.takeItem(row1, 0)
+        item2 = self.takeItem(row2, 0)
+        self.setItem(row1, 0, item2)
+        self.setItem(row2, 0, item1)
+
     def _context_menu(self, pos):
         self.menu = QtWidgets.QMenu(self)
         item = self.itemAt(pos)
@@ -354,15 +376,18 @@ def setup_ui(self):
             self.property_widgets.append(helper_widget)
 
         buttons_layout = QtWidgets.QHBoxLayout()
-        save_btn = QtWidgets.QPushButton("&Save", parent=self)
-        save_btn.setAutoDefault(True)
-        save_btn.setDefault(True)
-        save_btn.clicked.connect(self.save_changes)
+        self.save_btn = QtWidgets.QPushButton("&Save", parent=self)
+        self.save_btn.setAutoDefault(True)
+        self.save_btn.setDefault(True)
+        self.save_btn.clicked.connect(self.save_changes)
+        self.update_btn = QtWidgets.QPushButton("&Update", parent=self)
+        self.update_btn.clicked.connect(self.save_changes)
         cancel_btn = QtWidgets.QPushButton("&Cancel", parent=self)
         cancel_btn.clicked.connect(self.cancel_changes)
         buttons_layout.addStretch()
         buttons_layout.addWidget(cancel_btn)
-        buttons_layout.addWidget(save_btn)
+        buttons_layout.addWidget(self.update_btn)
+        buttons_layout.addWidget(self.save_btn)
 
         vlayout.addLayout(buttons_layout)
 
@@ -404,8 +429,10 @@ def save_changes(self):
                     helper._property_name,
                     helper.saved_value
                 )
+                print ("!!!!Failed to save!!\n")
 
-        self.accept()
+        if self.sender() == self.save_btn:
+            self.accept()
 
     @QtCore.Slot()
     def cancel_changes(self):