Always Check if there is Internet Connection Xamarin forms

Edit: this can be easily done with the new Xamarin Essentials Connectivity plugin, just follow the instructions there :D

Create a method in your App.cs (or App.xaml.cs) like this:

private async void CheckConnection()
{
    if(!CrossConnectivity.Current.IsConnected)
         await Navigation.PushAsync(new YourPageWhenThereIsNoConnection());
    else
         return;
}
    

And use it on your main app method like this:

public App()
{
    InitializeComponent();

    var seconds = TimeSpan.FromSeconds(1);
    Xamarin.Forms.Device.StartTimer(seconds,
        () =>
        {
             CheckConnection();
        });
}

Never used, but this is a documentation about the plugin you are using

Detecting Connectivity Changes

Often you may need to notify your user or respond based on network changes. You can do this by subscribing several different events.

Changes in Connectivity

When any network connectivity is gained, changed, or loss you can register for an event to fire:

/// <summary>
/// Event handler when connection changes
/// </summary>
event ConnectivityChangedEventHandler ConnectivityChanged; 
You will get a ConnectivityChangeEventArgs with the status if you are connected or not:

public class ConnectivityChangedEventArgs : EventArgs
{
  public bool IsConnected { get; set; }
}

public delegate void ConnectivityChangedEventHandler(object sender, ConnectivityChangedEventArgs e);
CrossConnectivity.Current.ConnectivityChanged += async (sender, args) =>
  {
      Debug.WriteLine($"Connectivity changed to {args.IsConnected}");
  };

Changes in Connectivity Type

When any network connectivity type is changed this event is triggered. Often it also is accompanied by a ConnectivityChanged event.

/// <summary>
/// Event handler when connection type changes
/// </summary>
event ConnectivityTypeChangedEventHandler ConnectivityTypeChanged;
When this occurs an event will be triggered with EventArgs that have the most recent information:

public class ConnectivityTypeChangedEventArgs : EventArgs
{
    public bool IsConnected { get; set; }
    public IEnumerable<ConnectionType> ConnectionTypes { get; set; }
}
public delegate void ConnectivityTypeChangedEventHandler(object sender, ConnectivityTypeChangedEventArgs e);
Example:

CrossConnectivity.Current.ConnectivityTypeChanged += async (sender, args) =>
  {
      Debug.WriteLine($"Connectivity changed to {args.IsConnected}");
      foreach(var t in args.ConnectionTypes)
        Debug.WriteLine($"Connection Type {t}");
  };