Question

Consider the following control (snipped for brevity):

public partial class ConfigurationManagerControl : UserControl
{

    public Func<string, bool> CanEdit { get; set;}
    public Func<string, bool> CanDelete { get; set; }

    public Dictionary<string, string> Settings
    {
        get { return InnerSettings; }
        set
        {
            InnerSettings = value;
            BindData();
        }
    }
    private Dictionary<string, string> InnerSettings;

    private void OnListIndexChanged(object sender, EventArgs e)
    {
        this.EditButton.Enabled = false;
        this.DeleteButton.Enabled = false;

        var indices = this.List.SelectedIndices;
        if (indices.Count != 1)
        {
            return;
        }

        var index = indices[0];
        var item = this.List.Items[index];

        if (this.CanEdit != null)
        {
            this.EditButton.Enabled = this.CanEdit(item.Text);
        }

        if (this.CanDelete != null)
        {
            this.DeleteButton.Enabled = this.CanDelete(item.Text);
        }

    }
}

There’s more to this control, but suffice it to say that it allows a user to add, edit, and delete the entries in a Dictionary<string, string>. In order to determine whether or not it should allow the user to edit or delete the entries, it uses the delegate method properties, CanDelete and CanEdit, which are provided by the form or control that hosts it:

public class SetupWizard : Form
{
    public SetupWizard()
    {
        InitializeComponent();

        this.SettingManager.CanEdit = CanEditSetting;
        this.SettingManager.CanDelete = CanDeleteSetting;
    }

    private static bool CanEditSetting(string item)
    {
        var lockedSettings = new[] { "LicenseHash", "ProductHash" };
        return !lockedSettings.Contains(item.ToLower());
    }

    private static bool CanDeleteSetting(string item)
    {
        var lockedSettings = new[] {
                                        "LicenseHash",
                                        "ProductHash", 
                                        "UserName", 
                                        "CompanyName"
                                    };
        return !lockedSettings.Contains(item.ToLower());
    }
}

I find that this design is both satisfactory and worrisome at the same time. On the one hand, it seems to solve the problem using the simplest solution that works (it certainly separates the concerns nicely). On the other hand, I have this nagging concern that I am using delegates improperly and should be using an event, instead (even though I do not need multiple listeners, and only need the caller to tell me if the item is editable).

And then, on the other other hand, there’s the chance that there’s a completely different design that I haven’t even considered that might solve the problem in a vastly superior way.

So. Is this design technically correct, maintainable, and flexible? Or should I be doing something better?

Answer 1

I suggest the use of an interface with these two methods. That’s a lot cleaner:

interface ICantThinkOfAGoodName
{
    bool CanEdit(string item);
    bool CanDelete(string item);
}

You could create something similar to the RelayCommand used in many MVVM frameworks:

public class RelayObject : ICantThinkOfAGoodName
{
    public RelayObject() : this(null, null) {}
    public RelayObject(Func<string, bool> canEdit, Func<string, bool> canDelete)
    {
        if(canEdit == null) canEdit = s => true;
        if(canDelete == null) canDelete = s => true;

        _canEdit = canEdit;
        _canDelete = canDelete;
    }

    public bool CanEdit(string item)
    {
        return _canEdit(item);
    }
    public bool CanDelete(string item)
    {
        return _canDelete(item);
    }
}

Use it like this:

public SetupWizard()
{
    InitializeComponent();

    this.SettingManager.PropertyName = new RelayObject(CanEditSetting, 
                                                       CanDeleteSetting);
    // or (all can be deleted)
    this.SettingManager.PropertyName = new RelayObject(CanEditSetting, null);
    // or (all can be edited)
    this.SettingManager.PropertyName = new RelayObject(null, CanDeleteSetting);
    // or (all can be edited and deleted)
    this.SettingManager.PropertyName = new RelayObject();

}

BTW: I am using Property injection here, because it is a control. Normally, I would pass the ICantThinkOfAGoodName dependency in the constructor of the ConfigurationManagerControl.