Writing the WebParts - The OPMLEditor WebPart

So in this blogpost, lets go ahead and write up a web part that lets you hold your OPML. To keep this short and to the point, I am going to skip over the basics, and provide you with enough links, so you could do the reading yourself.
• Like before, I setup a business object - RssSubscription, and a List is pretty much all I need to hold my RssSubscriptions. This business object had two properties - FeedName and FeedURL(both strings)
• Next, I set up writing the OPMLWebPart. To get me started, I created two RssSubscriptions, and added them to List rssUrls in the constructor. Here is the code -

public OPMLWebpart()
{
    rssUrls = new List<RssSubscription>();
    rssUrls.Add(new RssSubscription("Sahil Malik", "http://blah.winsmarts.com/rss2.aspx"));
    rssUrls.Add(new RssSubscription(" Events","sitename" ));
}

• With this private variable setup and populated, my rendering becomes very easy. I simply create a Radio Button List to allow the user to pick the RSS feed he wants as shown below, and add that to the Controls collection - thus they would get rendered automatically.

protected override void CreateChildControls()
{
    rbl = new RadioButtonList();
    foreach (RssSubscription feed in rssUrls)
    {
        rbl.Items.Add(new ListItem(feed.FeedName, feed.FeedURL));
    }
 
    rbl.AutoPostBack = true;
    this.Controls.Add(rbl);
    base.CreateChildControls();
}

• I also created a public property that is personlizable, so the user can specify his RSS Feeds.

[Personalizable(true)]
public List<RssSubscription> RssUrls
{
    get { return rssUrls; }
    set { rssUrls = value; }
}

Now since the above is a complex type, I need a custom editor, rather than a textbox to allow the user to specify his RSS Feeds in. I am going to only gloss over implementing the Editor here, for an in depth talk on Editors,

• In order to do so, I create a class which will be my Editor called OPMLEditor, that inherits from EditorPart.
• I make my OPMLWebPart implement IWebEditable, which requires me to add a method called CreateEditorPArts and WebBrowsableObject. These are implemented as shown below.

#region IWebEditable Members

EditorPartCollection IWebEditable.CreateEditorParts()
{
    List<EditorPart> editors = new List<EditorPart>();
    editors.Add(new OPMLEditor());
    return new EditorPartCollection(editors);
}
 
object IWebEditable.WebBrowsableObject
{
    get { return this; }
}

#endregion

• The Editor Part itself, is going to show a simple multiline textbox, in which the user can type his "FeedName, FeedURL" in a CSV format in a multi-line editor. The multiline editor is implemented as follows -  

protected override void CreateChildControls()
{
    opmlCSV = new TextBox();
    opmlCSV.TextMode = TextBoxMode.MultiLine;
    opmlCSV.Width = new Unit("300px");
    opmlCSV.Height = new Unit("100px");
    Controls.Add(opmlCSV);
}

• The two abstract methods that EditorPart will require you to implement are implemented as follows.

public override bool ApplyChanges()
{
    EnsureChildControls();
    OPMLWebpart part = WebPartToEdit as OPMLWebpart;
    if (part != null)
    {
        part.OPMLS = opmlCSV.Text;
    }
    else
    {
        return false;
    }
    return true;
}

public override void SyncChanges()
{
    EnsureChildControls();
    OPMLWebpart part = WebPartToEdit as OPMLWebpart;
    if (part != null)
    {
        opmlCSV.Text = part.OPMLS ;
    }
}

•And if you noticed, I just added a new property called OPMLS on the part. It's implementation simply converts the CSV into List as shown below.

public string OPMLS
{
    get
    {
        StringBuilder sb = new StringBuilder();
        foreach (RssSubscription subscription in rssUrls)
        {
            sb.Append(subscription.FeedName);
            sb.Append(",");
            sb.Append(subscription.FeedURL);
            sb.AppendLine();
        }
        return sb.ToString();
    }
    set
    {
        string opmls = value;
        rssUrls.Clear();
        String[] feeds = opmls.Split('\n');

        foreach (string feed in feeds)
        {
            String[] feedParts = feed.Split(',');
            RssSubscription subscription = new RssSubscription(feedParts[0], feedParts[1]);
            rssUrls.Add(subscription);
        }
    }

Great!! Compile and build this sucker, deploy it to your ASP.NET 2.0 WebPart framework based site, and run the website. Go ahead and set the page in "Catalog", and add the OPML Editor webpart to a WebPart Zone. This is shown as below.
You can see the two RssSusbcriptions I added in the constructor are pre-populated. The RSSImport webpart that appears below is what you already saw in this blogpost.
If you put the page in Edit display mode, you should also see the rudimentary but functional editor you just wrote in action. This can be seen as below.
Now when you set the page in Browse DisplayMode, you should be able to see the OPML Editor, and the RSS Rendering side by side as shown below.
What is disconcerting however at this time, is that for me to create an RSS-Reader, clicking on a Radio button should change the RSS URL of the RSS Rendering below. While selecting a particular RSS Feed does cause a postback, it doesn't update the RssUrl of the RSS Rendering Webpart.
This is because, at this time, these two Webparts Do not Communicate with each other.
So in the next blog post, I will talk about how to make these two web parts communicate. But for the meanwhile, I'd recommend brushing up on the basics of WebPart communication by reading -