MainActivity_OnCreate.cs

protected override void OnCreate(Bundle bundle)
{
    base.OnCreate(bundle);

    // Set our view from the "main" layout resource
    SetContentView(Resource.Layout.Main);

    _amount = 0.00m;
    _result = 0.00m;
    _numberOfPeople = 0;

    InitializeUserControls();
}

// ...

private void InitializeUserControls()
{
    _inputAmount = this.FindViewById<EditText>(Resource.Id.inputAmount);
    _inputNumberOfPeople = this.FindViewById<EditText>(Resource.Id.inputNumberOfPeople);
    _txtResultDecimal = this.FindViewById<EditText>(Resource.Id.txtResultDecimal);
    _btnCalculate = this.FindViewById<Button>(Resource.Id.btnCalculate);
}