Xamarin Forms TemplateBinding - xamarin

Question

I understand XAML doesn't really have a facility to extend (inherit) one page from another, but I have seen others use ControlTemplates to achieve this effect.
I am having trouble getting a Binding to work in this scenario. In my example, I have a base ContentPage extended by MainPage. Also, I am using FreshMVVM, so that is why the view model is minimal as FreshMVVM handles all the plumbing of property change notifications.
When the app runs, the label should get the value "Xamarin Forms Header" initialized in the MainPageModel.
I have the fully runnable source on github here, but here's the code. Can someone see what the issue is?
MainPage.xaml
<local:PageBase xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:local="clr-namespace:SampleApp"
x:Class="SampleApp.MainPage">
<StackLayout>
</StackLayout>
</local:PageBase>
MainPageModel.xaml
public class MainPageModel : FreshBasePageModel
{
public MainPageModel()
{
LabelText = "Xamarin Forms Header";
}
public string LabelText { get; set; }
}
PageBase.xaml
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="SampleApp.PageBase">
<ContentPage.ControlTemplate>
<ControlTemplate>
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
<RowDefinition Height="*" />
</Grid.RowDefinitions>
<Label Grid.Row="0" Text="{Binding LabelText}" />
<ContentPresenter Grid.Row="1" />
</Grid>
</ControlTemplate>
</ContentPage.ControlTemplate>
</ContentPage>

Answer 1

you could try to change like this:
MainPage.xaml :
<?xml version="1.0" encoding="utf-8" ?>
<local:PageBase xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:local="clr-namespace:SampleApp"
x:Class="SampleApp.MainPage"
LabelText ="{Binding LabelText} "
>
<StackLayout>
</StackLayout>
</local:PageBase>
PageBase.xaml:
<?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="SampleApp.PageBase">
<ContentPage.ControlTemplate>
<ControlTemplate>
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
<RowDefinition Height="*" />
</Grid.RowDefinitions>
<Label Grid.Row="0" Text="{TemplateBinding LabelText}" />
<ContentPresenter Grid.Row="1" />
</Grid>
</ControlTemplate>
</ContentPage.ControlTemplate>
</ContentPage>
in your PageBase.xaml.cs:
public partial class PageBase : ContentPage
{
public static readonly BindableProperty LabelTextProperty = BindableProperty.Create("LabelText", typeof(string), typeof(PageBase), "Control Template Demo App");
public string LabelText
{
get { return (string)GetValue(LabelTextProperty); }
}
public PageBase ()
{
InitializeComponent ();
}
}
you could refer to TemplateBinding

Answer 2

TemplateBinding doesn't bind to the View Model so whole code is fundamentally wrong, please read about the topic https://learn.microsoft.com/en-us/xamarin/xamarin-forms/app-fundamentals/templates/control-templates/template-binding
Also of note, this would likely work if you used Binding instead of TemplateBinding, but I don't think it makes sense to do that as said something is fundamentally wrong.