Wait for user selection from user interface

Question

I am making a custom maptool for QGIS I am overriding canvasReleaseEvent. when the user clicks on part of map canvas I call another function which identifies and creates a list of identified feature (there is some logic to create the list). Then this list is used to create the selection interface like the one below:

enter image description here

So far everything works well. The problem is,my program doesn't wait for the result from Selection Dialog box :

 def canvasReleaseEvent(self, event):
 parrent=self.select_parent_feature('structurepoint',event)
 #here the program should wait till the result from parrent is ready
 self.main_dlg.ParrentID_txt.setText(parrent)

Here is the function which creates the selection list, shows dlg and lets user to select

 def select_parent_feature(self,layer_name,e):
 '''This Functtion will show a list of all features in clicked point and returns user selection
 :param Layer_name: Qgis Layer name should be Already open.
 :type Layer_name: string
 :param e: is mouse event
 :type e: event
 '''
 #Start of creating list and identifieng the features
 global selection_list_header #this is the list of headers of table 
 selection=""
 selection_done_flag=False
 identified_parent_list=[]
 for lyr in QgsMapLayerRegistry.instance().mapLayers().values():
 if lyr.name() == layer_name:LayerID = lyr
 features = QgsMapToolIdentify(self.canvas).identify(e.x(), e.y(), [LayerID], QgsMapToolIdentify.TopDownAll)
 if len(features) > 0:#to make sure there is feature in clicked area
 if len(features)==1:#if there is only one item there is no need for the selection list
 feature = features[0].mFeature# the list only has one element
 selection=feature['id']
 selection_done_flag=True
 else: # show list to the user to select from
 for obj in features:
 feature = obj.mFeature
 info=[feature['id'],feature['size']]
 identified_parent_list.append(info)
 info=""
 table=self.selectionList_dlg.Selectionlist_tbl
 table.setColumnCount(len(selection_list_header))
 for i in range(len(identified_parent_list)):
 table.insertRow(i)
 column_index=0#the following line sets the headers
 for item in selection_list_header:
 table.setHorizontalHeaderItem(column_index, QTableWidgetItem(item))
 column_index+=1
 row_number=0#the following loop populates the value in table and lock the cells
 for item in identified_parent_list:
 for column_index in range(len(selection_list_header)):
 cell_value=QTableWidgetItem(item[column_index])
 cell_value.setFlags(QtCore.Qt.ItemIsEnabled)#lock the cell
 table.setItem(row_number,column_index,cell_value)
 row_number+=1
 #end of logic for createn selection list DLG
 #this it where my program doesnt work
 self.selectionList_dlg.show()
 result = self.main_dlg.exec_()
 # we need to wait for the result to be ready 
 if result:
 current_row_number=table.currentRow()
 if current_row_number<>-1:
 selection=table.item(current_row_number,0).text()#we asssumed the id is located on column 0
 selection_done_flag=True
 #I tried to use wait until and it explodes the program
 #while not selection_done_flag:#Wait till the user select from the list
 #time.sleep(0.0001)
 return selection 

As the program shows, I defined a flag to check and wait until the flag is true but that explodes the program.

the problem is the last part of the program where we show the selection list and the user has to select before the program can continue

Answer 1

It's difficult to tell exactly without the full code, but I noticed you're calling

self.selectionList_dlg.show()

I suspect this should be

self.selectionList_dlg.exec_()

As exec_ will wait till the dialog is closed, but show will not.

• Ehsan Aliverdi: there were several problems with code but the main problem was the difference between .show() and exec_()