Radovan Kozák Radovan Kozák - 1 month ago 34
C# Question

WPF MVVM command canexecute enable/disable button

I want to enable RibbonButton when textbox property text isn't null. Disable RibbonButton when textbox property text is null. I want to use CanExecute method in ICommand for it. How can I do it?

View:

<Custom:RibbonButton
LargeImageSource="..\Shared\img\save_diskete.png"
Label="Save"
Command="{Binding ButtonCommand}">
</Custom:RibbonButton>


ViewModel

class KomentarViewModel:BaseViewModel
{
#region Data
private ICommand m_ButtonCommand;
public ICommand ButtonCommand
{
get
{
return m_ButtonCommand;
}
set
{
m_ButtonCommand = value;
}
}
private string textKomentar;
public string TextKomentar
{
get
{
return this.textKomentar;
}
set
{
// Implement with property changed handling for INotifyPropertyChanged
if (!string.Equals(this.textKomentar, value))
{
textKomentar = value;
OnPropertyChanged("TextKomentar");
}
}
}
private ObservableCollection<Komentar> allCommentsInc;
public ObservableCollection<Komentar> AllCommentsInc
{
get
{
return allCommentsInc;
}
set
{
allCommentsInc = value;
OnPropertyChanged("AllCommentsInc");
}
}

public int idIncident { get; private set; }
public Incident incident { get; private set; }
#endregion

#region Constructor
public KomentarViewModel(int id)
{
CC_RK2Entities context = new CC_RK2Entities();
this.idIncident = id;

AllCommentsInc = new ObservableCollection<Komentar>(context.Komentar.Where(a => a.Incident_id == idIncident));
incident = context.Incident.Where(a => a.id == idIncident).First();

//ButtonCommand = new RelayCommand(new Action<object>(ShowMessage));
}
#endregion

#region Methods
//ukaz napsany text
public void ShowMessage(object obj)
{
//MessageBox.Show(obj.ToString());
MessageBox.Show(this.TextKomentar);
}
}


RelayCommand

namespace Admin.Shared.Commands
{
class RelayCommand : ICommand
{
private Action<object> _action;

public RelayCommand(Action<object> action)
{
_action = action;
}

#region ICommand Members

public bool CanExecute(object parameter)
{
return true;
}

public event EventHandler CanExecuteChanged;

public void Execute(object parameter)
{
_action(parameter);
}

#endregion
}
}

Answer

You need to modify your RelayCommand class like this

  class RelayCommand : ICommand
{
    private Action<object> _action;
    private Func<bool> _func;  

    public RelayCommand(Action<object> action,Func<bool> func)
    {
        _action = action;
        _func = func;
    }

    public void RaiseCanExecuteChanged()
    {
        if(CanExecuteChanged!=null)
            CanExecuteChanged(this,new EventArgs());
    }

    #region ICommand Members

    public bool CanExecute(object parameter)
    {
        if (_func != null)
            _func();
        return true;
    }



    public event EventHandler CanExecuteChanged;

    public void Execute(object parameter)
    {
        _action(parameter);
    }

    #endregion
}

Initialize ButtonCommand as

ButtonCommand = new RelayCommand((s) => ShowMessage(s),()=>!string.IsNullOrEmpty(TextKomentar));

RaiseCanExcuteChanged from the setter of Text property

        public string TextKomentar
    {
        get
        {
            return this.textKomentar;
        }
        set
        {
            // Implement with property changed handling for INotifyPropertyChanged
            if (!string.Equals(this.textKomentar, value))
            {
                textKomentar = value;
                OnPropertyChanged("TextKomentar");
            }
            ButtonCommand.RaiseCanExecuteChanged();
        }
    }