Is there any difference between these ICommand implementations?

Question

One way I've seen is this:

public class Command : ICommand
{
    Action<object> execute;
    Func<object, bool> canExecute;
    public Command(Action<object> execute, Func<object, bool> canExecute)
    {
        this.canExecute = canExecute;
        this.execute = execute;
    }
    public event EventHandler CanExecuteChanged
    {
        add { CommandManager.RequerySuggested += value; }
        remove { CommandManager.RequerySuggested -= value; }
    }
    public bool CanExecute(object parameter) => canExecute(parameter);
    public void Execute(object parameter) => execute(parameter);     
}

and the other I'm using is:

public class Command : ICommand
{
    Action<object> execute;
    Func<object, bool> canExecute;
    public Command(Action<object> execute, Func<object, bool> canExecute)
    {
        this.canExecute = canExecute;
        this.execute = execute;
        CommandManager.RequerySuggested += (o, e) => OnCanExecuteChanged();
    }
    public event EventHandler CanExecuteChanged;
    public void OnCanExecuteChanged() => CanExecuteChanged?.Invoke(null, EventArgs.Empty);
    public bool CanExecute(object parameter) => canExecute(parameter);
    public void Execute(object parameter) => execute(parameter);     
}

are both of these correct?

Answer 1

Hi,
try following demo and you can see RemoveHandler when Button will be destroyed.

XAML MainWindow:

<Window x:Class="WpfApp1.Window010"  
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"  
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"  
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"  
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"  
        xmlns:local="clr-namespace:WpfApp010"  
        mc:Ignorable="d"  
        Title="Window010" Height="450" Width="800">  
  <Window.DataContext>  
    <local:ViewModel/>  
  </Window.DataContext>  
  <StackPanel>  
    <Button Content="Change UC" Command="{Binding Cmd}" CommandParameter="ChangeUC"/>  
    <ContentControl Content="{Binding UC}"/>  
  </StackPanel>  
</Window>  

ViewModel and RelayCommand:

using System;  
using System.ComponentModel;  
using System.Runtime.CompilerServices;  
using System.Windows;  
using System.Windows.Controls;  
using System.Windows.Input;  
using WpfControlLibrary1;  
  
namespace WpfApp010  
{  
  public class ViewModel : INotifyPropertyChanged  
  {  
    public UserControl UC { get; set; }  
    public ICommand Cmd { get => new RelayCommand(CmdExec, CanCmdExec); }  
    private void CmdExec(Object parameter)  
    {  
      switch (parameter.ToString())  
      {  
        case "ChangeUC":  
          UC = new Window010UC1();  
          OnPropertyChanged(nameof(UC));  
          break;  
        default:  
          break;  
      }  
    }  
    private bool CanCmdExec(object obj) => true;  
  
    public event PropertyChangedEventHandler PropertyChanged;  
    private void OnPropertyChanged([CallerMemberName] string propName = "") => PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propName));  
  }  
  
  public class RelayCommand : ICommand  
  {  
    private readonly Predicate<object> _canExecute;  
    private readonly Action<object> _action;  
    public RelayCommand(Action<object> action) { _action = action; _canExecute = null; }  
    public RelayCommand(Action<object> action, Predicate<object> canExecute) { _action = action; _canExecute = canExecute; }  
    public void Execute(object o) => _action(o);  
    public bool CanExecute(object o) => _canExecute == null ? true : _canExecute(o);  
    public event EventHandler CanExecuteChanged  
    {  
      add { CommandManager.RequerySuggested += value; }  
      remove { CommandManager.RequerySuggested -= value; }  
    }  
  }  
}  

XAML UserControl:

<UserControl x:Class="WpfControlLibrary1.Window010UC1"  
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"  
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"  
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"   
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"   
             xmlns:local="clr-namespace:WpfControlLibrary1"  
             mc:Ignorable="d"   
             d:DesignHeight="450" d:DesignWidth="800">  
  <Grid>  
    <Button Content="Button in UserControl" Command="{Binding Cmd}"/>  
  </Grid>  
</UserControl>  

Result: