Sketcher: fixes #13999

src/Mod/Sketcher/Gui/DrawSketchControllableHandler.h

@@ -157,13 +157,15 @@ private:
         toolWidgetManager.resetControls();
     }
 
-    void onModeChanged() override
+    bool onModeChanged() override
     {
         DrawSketchHandler::resetPositionText();
         toolWidgetManager.onHandlerModeChanged();
-        DSDefaultHandler::onModeChanged();
-
-        toolWidgetManager.afterHandlerModeChanged();
+        if (DSDefaultHandler::onModeChanged()) {
+            // If onModeChanged returns false, then the handler has been purged.
+            toolWidgetManager.afterHandlerModeChanged();
+        }
+        return true;
     }
 
     void onConstructionMethodChanged() override

src/Mod/Sketcher/Gui/DrawSketchDefaultHandler.h

@@ -219,7 +219,10 @@ protected:
         }
     }
 
-    virtual void onModeChanged() {};
+    virtual bool onModeChanged()
+    {
+        return true;
+    };
 
 private:
     SelectModeT Mode;
@@ -479,8 +482,10 @@ protected:
      * 3. createAutoConstraints() : Must be provided with the commands to create autoconstraints
      *
      * It recomputes if not solves and handles continuous mode automatically
+     *
+     * It returns true if the handler has been purged.
      */
-    void finish()
+    bool finish()
     {
         if (this->isState(SelectMode::End)) {
             unsetCursor();
@@ -507,8 +512,9 @@ protected:
                 Base::Console().Error(e.what());
             }
 
-            handleContinuousMode();
+            return handleContinuousMode();
         }
+        return false;
     }
 
     /** @brief This function resets the handler to the initial state.
@@ -547,16 +553,18 @@ protected:
      *
      * It performs all the operations in reset().
      */
-    void handleContinuousMode()
+    bool handleContinuousMode()
     {
         if (continuousMode) {
             // This code enables the continuous creation mode.
             reset();
             // It is ok not to call to purgeHandler in continuous creation mode because the
             // handler is destroyed by the quit() method on pressing the right button of the mouse
+            return false;
         }
         else {
             sketchgui->purgeHandler();  // no code after, Handler get deleted in ViewProvider
+            return true;
         }
     }
     //@}
@@ -627,10 +635,11 @@ protected:
 
     /** @brief Default behaviour that upon arriving to the End state of the state machine, the
      * command is finished. */
-    void onModeChanged() override
+    bool onModeChanged() override
     {
         angleSnappingControl();
-        finish();  // internally checks that state is SelectMode::End, and only finishes then.
+        return !finish();  // internally checks that state is SelectMode::End, and only finishes
+                           // then.
     };
     //@}