使用asp.net用户控件按属性值对列表进行排序

Question

I am populating a div with many usercontrols, right now they are being added in the order that they are being read from the db. The UserControls markup looks like this:

<div class="Content_Thumb">

    <div class="Video_pic">
        <a href="tutorialname.aspx">
        <asp:Label ID="TutInfo" CssClass="CoverLbl_top" runat="server" Text="Label"></asp:Label>
        <asp:Label ID="TutInfo2" CssClass="CoverLbl_bottom" runat="server" Text="Description..."></asp:Label>
        <asp:Image ID="ThumbPic" CssClass="Thumb_Pic" runat="server" ImageUrl="/Images/Video_Thumb.png" />
        </a>
    </div>

    <div class="Thumb_Info">
        <asp:Label ID="Views" CssClass="ViewsLbl" runat="server" Text="680"></asp:Label>
        <asp:Label ID="Comments" CssClass="CommentsLbl" runat="server" Text="11"></asp:Label>
        <asp:Label ID="Likes" CssClass="LikesLbl" Style="TEXT-ALIGN: right" runat="server" Text="133"></asp:Label>
    </div>

    <div class="Thumb_Border">
            <asp:Image ID="UserPic" CssClass="Thumb_UploaderPic" runat="server" ImageUrl="/Images/Profile_Placeholder.png" />
            <a href="google.com">
                <asp:Label ID="UserLbl" CssClass="Thumb_UploaderInfo" runat="server" Text="Label"></asp:Label>
            </a>
    </div>

Then i've got these properties that are bound to the labels (some removed since i dont want to clutter the post).

        public string TutorialInfo 
    { 
        get; 
        set; 
    }

    public int TutorialViews
    {
        get;
        set;  
    }

    public override void DataBind()
    {
        TutInfo.Text = TutorialInfo;
        Views.Text = TutorialViews.ToString();
        Comments.Text = TutorialComments.ToString();
        Likes.Text = TutorialLikes.ToString();
        UserLbl.Text = TutorialUploader;
        base.DataBind();
    }

Now, what I want to do with these controls are to sort them by the property values. (highest number of views loads first etc). I'm currently at the stage where i've added them to a list, and now I'm trying to sort that list using LINQ's OrderBy like I saw on a post here.

List<UserControl> controls = new List<UserControl>();

        foreach (var Tutorial in dataconnection.Tutorial)
        {
            var control = LoadControl("~/WebUserControl1.ascx") as WebUserControl1;

            control.TutorialInfo = Tutorial.Title;
            control.TutorialComments = (int)Tutorial.Comments;
            control.TutorialViews = (int)Tutorial.Views;
            control.TutorialLikes = (int)Tutorial.Likes;
            control.TutorialUploader = Tutorial.Uploader;
            control.DataBind();
            //base.OnPreRender(e);
            ThumbTest.Controls.Add(control);
            controls.Add(control);
            var testcount = controls.Count();
            control.Visible = false;

        }

        var SortedList = controls.OrderBy(o => o.TutorialViews).ToList();

However i'm not able to access the properties even though they are public? "o.TutorialViews" is throwing an error. So how can i sort these controls?

I'm Fairly new to programming in general so my apologies if this turns out to be a silly mistake.

TLDR: How do I sort Usercontrols by property value.

Answer 1

Your list is a list of UserControl objects, which is the generic user control provided by ASP.NET:

List<UserControl> controls = new List<UserControl>();

The UserControl object doesn't have a property called TutorialViews , so you can't access that property on that type. However, you're adding custom user controls to the list:

var control = LoadControl("~/WebUserControl1.ascx") as WebUserControl1;

If every item in the list is going to be of type WebUserControl1 then you can declare the list itself with that type:

List<WebUserControl1> controls = new List<WebUserControl1>();

Since WebUserControl1 does define that property, you'll be able to access it.

Another approach might be to cast it when you access it, like this:

controls.OrderBy(o => ((WebUserControl1)o).TutorialViews)

But that's kind of messy and shouldn't be necessary. It's better to use the correct type in the first place.

Essentially, this is a symptom of the statically typed nature of C# (and many other languages). Type B inherits from Type A, so every instance of B is an instance of A. But not every instance of A is an instance of B, so you can't call a B property on an instance of A.

Think of an analogy... You have a list of Shape objects, and you populate it with Circle objects. This works, because Circle s are Shape s. But then you try to access the Radius property on an element in that list, and you get an error. This is because it's a list of Shape s and not every shape has a Radius . You'd need to either make it a list of Circle s or cast that element to a Circle for the compiler to know that there's a Radius .

For lots of further reading on the subject, take a look at Polymorphism and the Liskov Substitution Principle .