can I use lamda tothe ICommand in wpf?

Question

can I use lamda tothe ICommand in wpf?

mc 5,776

I am using mvvm in wpf and I wonder can I use this :

public ICommand MyCommand{get;}

public MainViewModel()
{
      MyCommand=(o,e)=>
       {
        };
}

and there will be error

and I have to use public MyRelayCommand:ICommand {} ?

Accepted answer

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Your answer

Answer 1

Hope you are doing good! Thank you for reaching out. Please find the answer below.

It sounds like you're trying to work with the ICommand interface in WPF while implementing the MVVM pattern.
The issue you're facing appears to be related to the incorrect way you are defining or using your ICommand. To clarify, you need a class that implements ICommand. A common pattern is to use a RelayCommand (or DelegateCommand) that wraps your lambda logic.

1. Create a RelayCommand class: First, you would need to create a class that implements ICommand. This is often referred to as a RelayCommand or DelegateCommand. Here's a quick example:

public class RelayCommand : ICommand
{
private readonly Action<object> _execute;
private readonly Predicate<object> _canExecute;

public RelayCommand(Action<object> execute, Predicate<object> canExecute = null)
   {
_execute = execute ?? throw new ArgumentNullException(nameof(execute));
_canExecute = canExecute;
}

public event EventHandler CanExecuteChanged
{
add { CommandManager.RequerySuggested += value; }
remove { CommandManager.RequerySuggested -= value; }
   }

public bool CanExecute(object parameter) => _canExecute == null || _canExecute(parameter);

public void Execute(object parameter) => _execute(parameter);
}

2. Use it in your ViewModel:

public ICommand MyCommand { get; }

public MainViewModel()
{
MyCommand = new RelayCommand(ExecuteMyCommand, CanExecuteMyCommand);
}

private void ExecuteMyCommand(object parameter)
{
// Your command logic here

}

private bool CanExecuteMyCommand(object parameter)
{
// Logic to determine if the command can execute
return true; // or some condition
}
And in your XAML, you can bind it like this:

This way, your command will correctly implement the Execute and CanExecute methods required by the ICommand interface, and your MainViewModel should work without errors.

If issue still persist after following all the steps, we’ll be happy to assist further if needed." Kindly mark the answer as accepted if the issue resolved".

Answer 2

Starry Night 110

public MainViewModel() { MyCommand=(o,e)=> { }; }

If we use the code above you shared in wpf, we could encounter the following error tip as you mentioned:

User's image

This error occurs if you try to assign or otherwise convert an anonymous method block to a type which is not a delegate type. Refer: Compiler Error CS1660 .

According to your description, do you want to use the Command as follows ,right?

            MyCommand = new Command<string>(fooObject =>
            {
                //add your code here, fooObject should have the passed value  
            });

But in maui, the class Command is a sealed class which has implemented the ICommand interface. User's image

And in wpf, we don't have such a class which has implemented the ICommand interface.

So if we want to use mvvm, we need to implement ICommand interface ourself which acts as Enhancement for the ICommand and extracts the boiler plate code to a separate class.

For how to use the ICommand Interface In MVVM - WPF, you can refer document : ICommand Interface In MVVM - WPF.

Starry Night 110

public MainViewModel() { MyCommand=(o,e)=> { }; }

If we use the code you posted, we could encounter such an error

User's image This error occurs if you try to assign or otherwise convert an anonymous method block to a type which is not a delegate type. Refer: Compiler Error CS1660.

Based on the description, do you want to use the Command just as follows, right? That is also the way used in Maui.

            MyCommand = new Command<string>(fooObject =>
            {
                //add your code here, fooObject should have the passed value  
            });

But in Maui , the class Command is a sealed class which has implemented interface ICommand. But in wpf, there is no such out-of-the-box class. We need to implement the interface ICommand ourself.

In wpf, we can create a class called RelayCommand which implements ICommand interface. This class acts as Enhancement for the ICommand and extracts the boiler plate code to a separate class.

For example:

    public class ViewModel
    {
        public ICommand MyCommand { get; set; }
        private string _name;
        public string Name
        {
            get { return _name; }
            set { _name = value; }
        }
        public ViewModel()
        {
             MyCommand = new RelayCommand(ExecuteMyMethod, CanExecuteMyMethod);
        }
        private bool CanExecuteMyMethod(object parameter)
        {
            if (string.IsNullOrEmpty(Name))
            {
                return false;
            }
            else
            {
                if (Name!="")
	            {
		            return true;
	            }
                else
                {
                    return false;
                }
            }
        }
        private void ExecuteMyMethod(object parameter)
        {
            MessageBox.Show("Hello...  " +Name);
        }        
    }

RelayCommand.cs

 public class RelayCommand:ICommand
    {
        Action<object> _execteMethod;
        Func<object, bool> _canexecuteMethod;
        public RelayCommand(Action<object> execteMethod, Func<object, bool> canexecuteMethod)
        {
            _execteMethod = execteMethod;
            _canexecuteMethod = canexecuteMethod;
        }
        public bool CanExecute(object parameter)
        {
            if(_canexecuteMethod != null)
            {
                return _canexecuteMethod(parameter);
            }
            else
            {
                return false;
            }
        }
        public event EventHandler CanExecuteChanged
        {
            add { CommandManager.RequerySuggested += value; }
            remove { CommandManager.RequerySuggested -= value; }
        }
        public void Execute(object parameter)
        {
            _execteMethod(parameter);
        }
    }

Usage:

<Window x:Class="MVVM_ICommand.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:viewmodel="clr-namespace:MVVM_ICommand.ViewModel"
        Title="MainWindow" Height="350" Width="525">
    <Window.Resources>
        <viewmodel:ViewModel x:Key="vm"></viewmodel:ViewModel>
    </Window.Resources>
    <StackPanel Orientation="Horizontal" VerticalAlignment="Center" HorizontalAlignment="Center" DataContext="{Binding Source={StaticResource vm}}">
        <TextBox Width="120" Height="30" Margin="10" Text="{Binding Path=Name , Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"></TextBox>
        <Button Width="90" Margin="10" Content="Click Me" Command="{Binding MyCommand}"></Button>   
    </StackPanel>
</Window>

Refer document: ICommand Interface In MVVM - WPF.

You can also check document: Basic MVVM and ICommand Usage Example.

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can I use lamda tothe ICommand in wpf?

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