Xamarin.Forms adding children to TabbedPage within OnBindingContextChanged - xaml

Question

I'm trying to implement a TabbedPage using MvvmCross for my navigation. The problem is MvvmCross uses ViewModel first navigation and this doesn't seem to play well with the general approach one might take to add children to a TabbedPage; because I do not have access to a non-null ViewModel during page construction, but I do have access to it within OnBindingContextChanged.
Here's what I have so far...
DashboardPage.xaml:
<?xml version="1.0" encoding="UTF-8"?>
<TabbedPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="DashboardPage"
xmlns:local="clr-namespace:CoreUI;assembly=CoreUI"
SelectedItem="{Binding CurrentSection, Mode=TwoWay}">
</TabbedPage>
DashboardPage.xaml.cs:
public partial class DashboardPage : TabbedPage
{
public DashboardPage()
{
InitializeComponent();
}
protected override void OnBindingContextChanged()
{
var vm = (BindingContext as DashboardViewModel);
if (vm == null)
{
return;
}
ObservableCollection<MainMenuSection> sections = vm.MenuSections;
foreach (var section in sections)
{
MainMenuViewModel main_menu_vm = new MainMenuViewModel
{
Section = section
};
// Question 2:
// Going against the MvvmCross grain here by referring to other pages from within a page, as opposed to doing everything from a ViewModel. How do I get around this?
Children.Add(new MainMenuPage(main_menu_vm));
}
}
}
MainMenuPage.xaml (pay attention to the comments here):
<?xml version="1.0" encoding="UTF-8"?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="MainMenuPage"
xmlns:local="clr-namespace:CoreUI;assembly=CoreUI"
Title="{Binding Title}" > <!-- The tabs that are displayed on Dashboard have the correct labels, so Binding appears to be working here. -->
<ContentPage.Content>
<StackLayout x:Name="Body" IsVisible="false">
<Label Text="{Binding Title}"/> <!-- Label doesn't get displayed, but does get displayed if Text is bound to something static, so Binding not quite working here. -->
</StackLayout>
</ContentPage.Content>
</ContentPage>
MainMenuPage.xaml.cs:
public partial class MainMenuPage : ContentPage
{
public MainMenuPage(MainMenuViewModel vm)
{
InitializeComponent();
BindingContext = vm;
}
protected override void OnBindingContextChanged()
{
Body.IsVisible = true;
}
}
The above MainMenuPage is a simplified version of what I have to illustrate my point, which is that I get a blank page for each tab within DashboardPage.
Question 1: Why are the tab pages blank?
Question 2: Refer to comment in DashboardPage.xaml.cs.

Answer 1

Why would you do this whole thing yourself? As you can see in the samples (https://github.com/MvvmCross/MvvmCross/tree/develop/TestProjects/Playground/Playground.Forms.UI/Pages) you can just decorate your view with a MvxTabbePagePresentation attribute and MvvmCross will handle the rest for you!
I would also advice to use the Mvx type pages to take advantage of lots of features.