close #86;

src/gui_qt/fit/result.py

@@ -64,8 +64,6 @@ class QFitResult(QtWidgets.QDialog, Ui_Dialog):
 
         self.cmap = RdBuCMap(vmin=-1, vmax=1)
 
-        self.buttonBox.accepted.connect(self.accept)
-
         self.graph_checkBox.stateChanged.connect(lambda x: self.graph_comboBox.setEnabled(x == QtCore.Qt.Unchecked))
 
         self.logy_box.stateChanged.connect(lambda x: self.fit_plot.setLogMode(y=bool(x)))
@@ -315,22 +313,27 @@ class QFitResult(QtWidgets.QDialog, Ui_Dialog):
             parts = self.partial_checkBox.checkState() == QtCore.Qt.Checked
 
             extrapolate = [None, None, None]
+            error = []
             if self.extrapolate_box.isChecked():
                 try:
                     extrapolate[0] = float(self.minx_line.text())
-                except TypeError:
-                    pass
+                except (TypeError, ValueError):
+                    error.append('Start value is missing')
                 try:
                     extrapolate[1] = float(self.maxx_line.text())
-                except TypeError:
-                    pass
+                except (TypeError, ValueError):
+                    error.append('End value is missing')
                 try:
                     extrapolate[2] = int(self.numx_line.text())
-                except TypeError:
-                    pass
+                except (TypeError, ValueError):
+                    error.append('Number of points is missing')
 
-            self.closed.emit(self._results, self._opts, graph, plot_fits, parts, extrapolate)
-            self.accept()
+            if error:
+                msg = QtWidgets.QMessageBox.warning(self, 'Error', 'Extrapolation failed because:\n' + '\n'.join(error))
+                return
+            else:
+                self.closed.emit(self._results, self._opts, graph, plot_fits, parts, extrapolate)
+                self.accept()
 
         else:
             self.reject()