How to Access SelectedItem in one Page on a Separate Page - wpf

Question

I have two datagrids separately on two pages, say a parentgrid on a parent-page and a childgrid on a child-page. how to access the selecteditem of parent-page to the child-page ?
when the both the datagrids are placed on the same page, the selecteditem works. but when I place the grids separately on each page, it doesn't work.
XAML for the ParentPage
<Grid.Datacontext>
<local:MainViewModel/>
</Grid.Datacontext>
<DataGrid AutoGenerateColumns="False" ItemsSource="{Binding Persons}" SelectedItem="{Binding SelectedHost, Mode=TwoWay}" SelectionChanged="DataGrid_SelectionChanged"/>
codebehind for the ParentPage
private void DataGrid_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
ChildPage _page = new ChildPage();
this.NavigationService.Navigate(_page);
}
XAML for child page
<DataGrid x:Name="ChildDatagrid" Margin="12,104,81,266" ItemsSource="{Binding Details}"/>
MainViewModel
//Datacontext
public MainViewModel()
{
this.Persons = Person.GetPersons();
}
// for Person Datagrid
private ObservableCollection<Person> personValues;
public ObservableCollection<Person> Persons
{
get { return personValues; }
set { this.SetProperty<ObservableCollection<Person>>(ref this.personValues, value); }
}
//for the PersonDetails datagrid
public ObservableCollection<PersonDetails> Details
{
get
{
if (this.Selectedperson == null)
{
return null;
}
return this.LoadDetails(this.Selectedperson.PersonID);
}
}
// method to load the persondetails data
private ObservableCollection<PersonDetails> LoadDetails(int personID)
{
ObservableCollection<PersonDetails> details = new ObservableCollection<PersonDetails>();
foreach (PersonDetails detail in PersonDetails.GetDetails().Where(item => item.PersonID == personID))
{
details.Add(detail);
}
return details;
}
// SelectedPerson Property
private Person selectedPersonValue;
public Person Selectedperson
{
get { return selectedPersonValue; }
set
{
this.SetProperty<Person>(ref this.selectedPersonValue, value);
this.RaiseNotification("Details");
}
}

Answer 1

You should make a ViewModel or Object, pass them into both pages and bind your grids to it. This way they will stay in sync.
Alternate option is to use and EventAggregator to sent messages between your pages.
If you're using WPF you should take a look into Prism. A lot of build-in functionality exists.

Answer 2

EDIT: Post changed to reflect new information;
I've never used the NavigationService with WPF before, so I'm not 100% sure what is available to you, so apologies if I miss something.
However, if you move your Details Collection to your Child Form, and make it a standard property;
private ObservableCollection<PersonDetails> _Details;
public ObservableCollection<PersonDetails> Details {
get { return _Details; }
set {
if (value.Equals(_Details) == false)
{
_Details = value;
OnPropertyChanged("Details");
}
}
}
Assuming you have a reference to your MainViewModel, you can then navigate to your page using;
private void DataGrid_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
ChildPage _page = new ChildPage();
_page.Details = MainViewModel.LoadDetails(PersonID);
this.NavigationService.Navigate(_page);
}
As a note, I don't like the idea of calling the Navigiate Service from the Code behind, as this makes the code messy and difficult to test.
Jesse Liberty has a nice post on using the MVVM Light Framework, and allowing the ViewModel to call the Navigate Service Directly;
http://jesseliberty.com/2012/01/17/calling-navigate-from-the-view-model/