试图通过使用委托实现观察者，我得到错误:不能隐式转换类型'void'到我的委托所属的类

// subject 
class SafeMode
{
    private bool m_enable = false;
    public bool Disable()
    {
        return m_enable;
    }
    public delegate void NotifyObserversHandler(bool _status);
    public event NotifyObserversHandler DiableCommands;
    public void Notify()
    {
        DiableCommands(m_enable);
    }
}

public interface ICommand
{
    void Execute(User i_User, string i_ButtonText, List<Photo> o_Photos);
    void DiableFunctionality();
}
// my only observer
public class MostPopularPic : ICommand
{
    public void DisableFunctionality()
    {
        m_enable = false;
    }
}

// at other form class that's where i  attach my observer to the delegate and the error occurs. 
foreach( KeyValuePair<string,ICommand> runner in tmp)
{
    ICommand curr = runner.Value;
    m_safer.DiableCommands += curr.DiableFunctionality();
    // faild to convert 'void' to  'SafeMode.NotifyObserversHandler' 
}