There are many best practices in writing Xamarin. Here are some that we’ve canonized where I work…

👍 By convention the identifier for the ViewModel is vm

😠 Do not assign more than one page to a view model. Generally speaking: it should be one page to one view model

😠 Do not pass view modes to methods of other pages

👍 The only code in code-behind (e.g., foo.xaml.cs) should be

initialize in the constructor
create the view model
assign the datacontext to the view model
call the viewmodel’s Initialize method
Lifecycle methods such as OnAppearing and OnDisappearing

Why: we want to keep the code behind as sparse as possible. Unit testing requires reaching into code and that is infinitely easier with a viewmodel.

👍 Every ViewModel should have an initialize method.

Why: Having an initialize method keeps most of the code for the vm out of the constructor. This is recommended practice by Microsoft, and allows for async methods.

😠 Do not put Xaml in templates in App.xaml. Put the Xaml in the Xaml file.

Why: App.xaml quickly becomes bloated and hard to work with. Having the Xaml in the Xaml file is natural and helps create the troika we want: foo.xaml, foo.xaml.cs and fooViewModel.cs.

👍 Create viewmodel name by appending “viewmodel” to the xaml name

LigthController.xaml
  LightController.xaml.cs
     LightControllerViewModel.cs

Why: It is far easier to find the file you want if we follow a convention.

😠 Avoid Xaml file names ending in “view”

LightControllerView.xaml
   LightControllerView.xaml.cs
      LightControllerViewViewModel.cs

Why: Adding view to a view file is redundant and it makes reading the name of the ViewModel more difficult.

👍 Use commands rather than event handlers

// wrong - handled in code behind
<button Text="Divide by 2" Clicked="onClick" />  

//correct - handled in viewmodel
<button Text="Divide by 2" ClickedCommand="{Binding DivideBy2Command"