Unhandled Exception: System.InvalidCastException: Specified cast is not valid. occurred ERROR in Xamarin

Question

I have a SwitchCell implemented within a ListView; I want to be able to access the properties of the SwitchCell: On and text. I want to be able to get and set the OnProperty of the SwitchCell to change/read the Switch state from within the xaml.cs class.

when I run the code, I get the Unhandled Exception error. i am very new to both Xamarin and C# so any help/advise/examples of solving the problem will be greatly appreciated.

The exception is happening at var selectedItem = ((SwitchCell)sender).BindingContext as Relays; in the SwitchCell.xaml.cs.

My Relay.cs class is as follows:

using System;
using System.Collections.Generic;
using System.Text;

namespace Socket.Models
{
    public class Relays
    {
      public Boolean isOn { get; set; }       // Set the state of the 
                                                switch 

      public string State { get; set; }       // Get the state of the 
                                     switch based on the isOn property

      public string Name { get; set; }        // Set the name of the 
                                               relay in the list

      }
   }

My SwitchCell.xaml is as follows:

  <?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="Socket.SwitchCell"
         Title="Relay Control Page">

<ContentPage.Content>
    <StackLayout Padding="10,0,0,0">

        <ListView x:Name="lstView" SelectionMode="None">
            <ListView.ItemTemplate>
                <DataTemplate>
                    <SwitchCell x:Name="Sw1" Text="{Binding Name}" On=" 
                             {Binding isOn, Mode=TwoWay}" 
                                OnChanged="SwitchCell_OnChanged_2"/>
                </DataTemplate>
            </ListView.ItemTemplate>
        </ListView>

        </StackLayout>
    </ContentPage.Content>
</ContentPage>

My SwitchCell.xaml.cs is as follows:

  using Socket.Models;
  using System;
  using System.Collections.Generic;
  using System.Collections.ObjectModel;
  using System.ComponentModel;
  using System.Linq;
  using System.Runtime.CompilerServices; 
  using System.Text;
  using System.Threading.Tasks;
  using Xamarin.Forms;
  using Xamarin.Forms.Xaml;

namespace Socket
{
    [XamlCompilation(XamlCompilationOptions.Compile)]

public partial class SwitchCell : ContentPage
{

    public SwitchCell ()
    {
        InitializeComponent ();
        loadSampleData();
    }

    private void loadSampleData()
    {
        // Create sample data

        ObservableCollection<Relays> listRelays = new 
          ObservableCollection<Relays>();

        listRelays.Add(new Relays { Name ="Relay 1", State = "", 
                 isOn=false });
        listRelays.Add(new Relays { Name ="Relay 2", State = "", 
                 isOn=false });
        listRelays.Add(new Relays { Name ="Relay 3", State = "", 
                 isOn=false });

        lstView.ItemsSource = listRelays;

    }

    private void SwitchCell_OnChanged_2(object sender, ToggledEventArgs 
                                                                e)
    {
        var selectedItem = ((SwitchCell)sender).BindingContext as 
                                        Relays;

        if (true)
        {            
            bool IsToggled = e.Value;
            string name = IsToggled.ToString();

            if (name == "True")
            {
                //DisplayAlert("ON", "Relay 1 On", "Cancel");
                BackgroundColor = Color.Silver;

                if (selectedItem.isOn == false)
                {
                    BackgroundColor = Color.Gold;
                    selectedItem.Name = "Changed";
                }
            }

            else
            {
                //DisplayAlert("OFF", "Relay 1 OFF", "Cancel");
                BackgroundColor = Color.LightSkyBlue;
            }

            }

        }       

    }

}

This is the error I get in VS 2017: Unhandled Exception: System.InvalidCastException: Specified cast is not valid. occurred.

I am not sure if this is useful but this is what I get from the Call Stack:

0x1 in Socket.SwitchCell.SwitchCell_OnChanged_2 at C:\Users\ryno\Desktop\Xamarin\Socket\Socket\Socket\SwitchCell.xaml.cs:42,13.

I have no idea what I am doing wrong. Any help will be appreciated. Thanks.

the debugger should show you which line caused the exception. Or, is it happening immediately when the page loads, or only after you do something? — Jason
Can you copy and paste the error and the stacktrace. that should help — User1
Try renaming the page class (both in xaml and the codebehind) to something other than SwitchCell... (there is probably a name collision with the XAML ListView SwitchCell control) — Benl
It is happening at this line var selectedItem = ((SwitchCell)sender).BindingContext as Relays. Sorry, I forgot to add that to the question. — Ryno

Gerald Versluis Gerald Versluis · Accepted Answer · 2018-07-24T14:55:41

Only cast that seems to happen is here: var selectedItem = ((SwitchCell)sender).BindingContext as Relays;

Check if sender is indeed a SwitchCell.

Unhandled Exception: System.InvalidCastException: Specified cast is not valid. occurred ERROR in Xamarin

2 Answers