RelayCommand parameter passing in Xamarin

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无人共我 2021-01-14 05:12

I am very new to Xamarin cross-platform and while I did have some experience with WPF and MVVM I am still having issue understanding p

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佛祖请我去吃肉 (楼主)

2021-01-14 05:14

Relay or Delegate Command for Xamarin

That's how I achieve it, I hope it'll be helpful for someone

public class DelegateCommand : ICommand
{
    /// 
    /// The _execute
    /// 
    private readonly Action _execute;

    /// 
    /// The _can execute
    /// 
    private readonly Func _canExecute;

    /// 
    /// Initializes a new instance of the  class.
    /// 
    /// The execute.
    /// The can execute.
    /// execute
    public DelegateCommand(Action execute, Func canExecute)
    {
        _execute = execute ?? throw new ArgumentNullException("execute");

        if (canExecute != null)
        {
            this._canExecute = canExecute;
        }
    }

    /// 
    /// Initializes a new instance of the DelegateCommand class that
    /// can always execute.
    /// 
    /// The execution logic.
    /// If the execute argument is null.
    public DelegateCommand(Action execute)
        : this(execute, null)
    {
    }

    /// 
    /// Occurs when changes occur that affect whether the command should execute.
    /// 
    public event EventHandler CanExecuteChanged;


    /// 
    /// Raises the can execute changed.
    /// 
    public void RaiseCanExecuteChanged()
    {

        CanExecuteChanged?.Invoke(this, EventArgs.Empty);
    }

    /// 
    /// Defines the method that determines whether the command can execute in its current state.
    /// 
    /// Data used by the command.  If the command does not require data to be passed, this object can be set to null.
    /// true if this command can be executed; otherwise, false.
    public bool CanExecute(object parameter)
    {
        return _canExecute == null || _canExecute.Invoke();
    }

    /// 
    /// Defines the method to be called when the command is invoked.
    /// 
    /// Data used by the command.  If the command does not require data to be passed, this object can be set to null.
    public virtual void Execute(object parameter)
    {
        if (CanExecute(parameter))
        {
            _execute.Invoke();
        }
    }
}

/// 
/// This class allows delegating the commanding logic to methods passed as parameters,
/// and enables a View to bind commands to objects that are not part of the element tree.
/// 
/// Type of the parameter passed to the delegates
public class DelegateCommand : ICommand
{
    /// 
    /// The execute
    /// 
    private readonly Action _execute;

    /// 
    /// The can execute
    /// 
    private readonly Predicate _canExecute;

    /// 
    /// Initializes a new instance of the  class.
    /// 
    /// The execute action.
    /// execute
    public DelegateCommand(Action execute)
        : this(execute, null)
    {
    }

    /// 
    /// Initializes a new instance of the  class.
    /// 
    /// The execute.
    /// The can execute predicate.
    /// execute
    public DelegateCommand(Action execute, Predicate canExecute)
    {
        _execute = execute ?? throw new ArgumentNullException("execute");

        if (canExecute != null)
        {
            _canExecute = canExecute;
        }
    }

    /// 
    /// Occurs when changes occur that affect whether the command should execute.
    /// 
    public event EventHandler CanExecuteChanged;

    /// 
    /// Raise  event.
    /// 
    public void RaiseCanExecuteChanged()
    {
        CanExecuteChanged?.Invoke(this, EventArgs.Empty);
    }

    /// 
    /// Determines whether this instance can execute the specified parameter.
    /// 
    /// The parameter.
    /// true if this instance can execute the specified parameter; otherwise, false.
    public bool CanExecute(object parameter)
    {
        return _canExecute == null || _canExecute.Invoke((T)parameter);
    }

    /// 
    /// Executes the specified parameter.
    /// 
    /// The parameter.
    public virtual void Execute(object parameter)
    {
        if (CanExecute(parameter))
        {
            _execute((T)parameter);
        }
    }
}

in Your View

in Your View Model

public ICommand LoginCommand { get; }
LoginCommand = new DelegateCommand