Question

I’m building an MVVM application in WPF and I am binding a Menu to a MenuItem model. My MenuItem class has these properties :

public class MenuItem
{
    private List<MenuItem> _Items;

    public MenuItem(string header, ICommand command)
    {
        Header = header;
        Command = command;
    }

    public MenuItem()
    {

    }

    public string Header { get; set; }

    public List<MenuItem> Items
    {
        get { return _Items ?? (_Items = new List<MenuItem>()); }
        set { _Items = value; }
    }

    public ICommand Command { get; set; }
    public string CommandName { get; set; }
    public object Icon { get; set; }
    public bool IsCheckable { get; set; }
    public bool IsChecked { get; set; }
    public bool Visible { get; set; }
    public bool IsSeparator { get; set; }
    public string ToolTip { get; set; }
    public int MenuHierarchyID { get; set; }
    public int ParentMenuHierarchyID { get; set; }
    public string IconPath { get; set; }
}

This MenuItem model class is populated from Data coming from a database. In this
case, the only property populated from DB is CommandName.

Let’s say it populates it with the string “OpenFile”

EDIT
Here my MenuViewModelConstructor:

    public MenuViewModel(MainViewModel _MainViewModel)
    {
       ....
    }

It has a dependency to MainViewModel because that’s where the OpenFile and CanOpenFile methods live.

My MenuViewModel has a method to register Commands as follows:

        private void RegisterMenuCommand(MenuItem item)
        {
            if(!string.IsNullOrEmpty(item.CommandName))
            {
                //How can I create a new RelayCommand instance from
                //my CommandName string???? 
                //e.g. item.Command = new RelayCommand(_MainViewModel.<item.CommandNameHere>, _MainViewModel."Can" + <item.CommandNameHere>
                item.Command = new RelayCommand(_MainViewModel.OpenFile, _MainViewModel.CanOpenFile);
            }

            foreach(MenuItem child in item.Items)
            {
                RegisterMenuCommand(child);
            }
        }

By the way, the signature of RelayCommand is:

public RelayCommand(Action execute, Func<bool> canExecute)

Is it possible to instantiate my RelayCommand with Reflection or dynamic lambdas or something like that so I can use my Command string coming from the database at runtime dynamically? What would be the most optimal way?

EDIT: SOLUTION
Thanks to @Nathan for pointing me to the right solution, here is my working method:

    private void RegisterMenuCommand(MenuItem item)
    {
        if(!string.IsNullOrEmpty(item.CommandName))
        {
            MethodInfo method1 = _MainViewModel.GetType().GetMethod(item.CommandName);
            Delegate d1 = Delegate.CreateDelegate(typeof(Action),_MainViewModel, method1);

            MethodInfo method2 = _MainViewModel.GetType().GetMethod("Can" + item.CommandName);
            Delegate d2 = Delegate.CreateDelegate(typeof (Func<bool>),_MainViewModel, method2);

            item.Command = new RelayCommand((Action)d1, (Func<bool>)d2);
        }

        foreach(MenuItem child in item.Items)
        {
            RegisterMenuCommand(child);
        }
    }

I am using .NET 4.0

Thanks!

Answer 1

I did a quick google search on creating delegates with reflection and found this pretty good article How to: Hook Up a Delegate Using Reflection

I created a quick test on my local machine and got it to work

MethodInfo miHandler = typeof(MainWindow).GetMethod("OpenCommandHandler", BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Public);
Delegate d = Delegate.CreateDelegate(typeof(Action<object>), this, miHandler);
btnTest.Command = new DelegateCommand((Action<object>)d);

where this in CreateDelegate is the view I was working from (MainWindow)

You’ll have to tweak it a bit to get your’s to work but I imagine it would be something like:

var obj = <object containing your method>

MethodInfo miHandler = typeof(obj).GetMethod(item.CommandName, BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Public);
Delegate openDelegate = Delegate.CreateDelegate(typeof(Action), obj, miHandler);
item.Command = new RelayCommand((Action)openDelegate, ...);