Create view model and set binding context in view's XAML

Example.xaml

<!-- From https://github.com/jamesmontemagno/app-pretty-weather/blob/master/PrettyWeather/PrettyWeather/MainPage.xaml -->
<?xml version="1.0" encoding="utf-8" ?>
<ContentPage
    x:Class="PrettyWeather.MainPage"
    xmlns="http://xamarin.com/schemas/2014/forms"
    xmlns:pancake="clr-namespace:Xamarin.Forms.PancakeView;assembly=Xamarin.Forms.PancakeView"
    xmlns:converters="clr-namespace:PrettyWeather.Converters"
    xmlns:viewmodel="clr-namespace:PrettyWeather.ViewModel"
    xmlns:model="clr-namespace:PrettyWeather.Model"
    xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
    xmlns:d="http://xamarin.com/schemas/2014/forms/design"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    x:Name="WeatherPage"
    mc:Ignorable="d">
    <ContentPage.BindingContext>
        <viewmodel:WeatherViewModel Temp="61"/>
    </ContentPage.BindingContext>