XAML

  <ContentPage.BindingContext>
        <vm:MapNavigarionVM />
    </ContentPage.BindingContext>

    <ContentPage.Content>
        <StackLayout>
            <Label Text="Where do you want to go"
                   FontSize="Body"
                   HorizontalTextAlignment="Center"
                   Margin="0,30,0,0"/>
            <StackLayout Orientation="Horizontal">
                 <Label Text="From: "
                   Margin="30,30,0,0"/>
                <combobox:SfComboBox HeightRequest="40"
                                     HorizontalOptions="FillAndExpand"
                                     x:Name="NavigationFrom"
                                     SelectedItem="{x:Binding SelectedItemFrom}"
                                     DisplayMemberPath="street"
                                     IsEditableMode="False"
                                     Margin="0,0,30,0"/>
            </StackLayout>
            <StackLayout Orientation="Horizontal"
                         Margin="0,30,0,0">
                <Label Text="To: "
                       Margin="30,30,0,0" />
                <combobox:SfComboBox HeightRequest="40"
                                     IsEditableMode="False"
                                     HorizontalOptions="FillAndExpand"
                                     x:Name="NavigationTo"
                                     SelectedItem="{x:Binding SelectedItemTo}"
                                     DisplayMemberPath="street"
                                     Margin="0,0,30,0" />
            </StackLayout>
        </StackLayout>
    </ContentPage.Content>



VM

private Address _SelectedItemFrom;
        public Address SelectedItemFrom {
            get { return _SelectedItemFrom; }
            set
            {
                if (_SelectedItemFrom != value) {
                    _SelectedItemFrom = value;
                    RaisePropertyChanged();
                    getCoordinatesAsync("from");
                }
            }
        }


        private Address _SelectedItemTo;
        public Address SelectedItemTo {
            get { return _SelectedItemTo; }
            set
            {
                if (_SelectedItemTo != value) {
                    _SelectedItemTo = value;
                    RaisePropertyChanged();
                    getCoordinatesAsync("to");
                }
            }
        }

        private async void getCoordinatesAsync(string ToOrFrom) {

            try {
                if (ToOrFrom.Equals("to")) {
                    var address = $"{SelectedItemTo.street} , {SelectedItemTo.city} , {SelectedItemTo.state}";
                    var locations = await Geocoding.GetLocationsAsync(address);
                    var location = locations?.FirstOrDefault();
                    if (location != null) {
                        SelectedItemTo.Lat = location.Latitude;
                        SelectedItemTo.lon = location.Longitude;
                    }
                } else if (ToOrFrom.Equals("from")) {
                    var address = $"{SelectedItemFrom.street} , {SelectedItemFrom.city} , {SelectedItemFrom.state}";
                    var locations = await Geocoding.GetLocationsAsync(address);
                    var location = locations?.FirstOrDefault();
                    if (location != null) {
                        SelectedItemFrom.Lat = location.Latitude;
                        SelectedItemFrom.lon = location.Longitude;
                    }
                }
            } catch (Exception ex) {
                await Application.Current.MainPage.DisplayAlert("Error", ex.Message, "OK");
            }
        }
    }