How to pass & read command parameter in viewmodel

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How to pass & read command parameter in ViewModel

C#

<StackPanel Grid.Column="1" Orientation="Horizontal" HorizontalAlignment="Center" VerticalAlignment="Center">
                <RadioButton x:Name="rbOTP" Content="Use Login OTP" Tag="1"  Padding="12,8,12,8" GroupName="OTPOption" Style="{StaticResource StashOTPOption}" 
                             ToolTip="Recieve OTP via email" IsChecked="True" Command="{Binding OTPOptionCommand}" CommandParameter="{Binding ElementName=rbOTP, Path=Tag}"/>
                
                <RadioButton x:Name="rbLoginCode" Content="Use Login Code" Tag="2" Padding="12,8,12,8" GroupName="OTPOption" Style="{StaticResource StashOTPOption}" 
                             ToolTip="Use pre-generated login codes" Command="{Binding OTPOptionCommand}" CommandParameter="{Binding ElementName=rbLoginCode, Path=Tag}"/>
                
                <RadioButton x:Name="rbPin" Content="Use Secret Pin" Tag="3" Padding="12,8,12,8" GroupName="OTPOption" Style="{StaticResource StashOTPOption}"
                             ToolTip="Use secret pin" Command="{Binding OTPOptionCommand}" CommandParameter="{Binding ElementName=rbPin, Path=Tag}"/>
            </StackPanel>

C#

//OTP Option
private ICommand _otpOptionCommand;

public ICommand OTPOptionCommand
{
  get 
  { 
   if (_otpOptionCommand == null)
   {
     _otpOptionCommand = new RelayCommand(SetOtpOption, CanSetOtpOption);
   }
   return _otpOptionCommand;
  }
}

private bool CanSetOtpOption(object obj)
{
  return true;
}

private void SetOtpOption(object obj)
{
  //Set the OTPOption value to the checked radio button tag value
}

What I have tried:

I tried binding the property to each radio button IsChecked and used a boolean to int converter

Posted 18-Feb-23 17:00pm

Christopher Fernandes

Updated 18-Feb-23 17:24pm

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Comments

George Swan 19-Feb-23 2:55am

Your code looks ok to me. The type passed to the SetOtpOption(object obj) method is a string. You need to cast that to an int like this: int tag = int.Parse((string)obj);

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Graeme_Grant · Answer 1 · 2023-02-18T17:24:00

Use the MVVM ToolKit[^]. One of the thinks that they have is a RelayCommand[^] that will make life simple for you.

But if you want to roll-your-own, here is one that I use:

C#

public class RelayCommand : RelayCommand<object>
{
    public RelayCommand(Action<object> execute)
        : base(execute) { /* skip */ }

    public RelayCommand(Action<object> execute, Predicate<object>? canExecute)
        : base(execute, canExecute) { /* skip */ }
}

public class RelayCommand<TValue> : ICommand
{
    #region Fields

    private readonly Action<TValue> _execute;
    private readonly Predicate<TValue>? _canExecute;
    private EventHandler? _internalCanExecuteChanged;

    #endregion

    #region Constructors

    public RelayCommand(Action<TValue> execute)
        : this(execute, null) { /* skip */ }

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

    #endregion

    #region ICommand Members

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

    // ref: https://stackoverflow.com/a/8475103/327541
    // This method can be used to raise the CanExecuteChanged handler.
    // This will force WPF to re-query the status of this command directly.
    public void RaiseCanExecuteChanged()
    {
        if (_canExecute != null)
            OnCanExecuteChanged();
    }

    public void Execute(object? parameter)
        => _execute((parameter is null ? default : (TValue)parameter)!);

    public bool CanExecute(object? parameter)
        => _canExecute == null || (parameter is null ?  _canExecute(default!) : _canExecute((TValue)parameter));

    protected virtual void OnCanExecuteChanged()
    {
        EventHandler? eCanExecuteChanged = _internalCanExecuteChanged;
        if (eCanExecuteChanged == null)
            return;

        eCanExecuteChanged(this, EventArgs.Empty);
    }

    #endregion
}

To use...

1. declare a property:

C#

public RelayCommand MyCommand { get; set; }

2. Initialise in the constructor:

C#

MyCommand = new RelayCommand(execute: MyMethod, canExecute: _ => true);

3. The Method that executes:

C#

private void MyMethod(object obj)
{
    // do work here...
}