How to Publish Content from Another URL in a ContentPlaceHolder Control
It seems like every week I see a person asking a question about either placing content in the ContentPlaceHolder control dynamically or from another URL in the www.asp.net forums. By URL they typically mean another page from another site. I think many of these folks are somewhat misguided as to what Master Pages are meant to solve and how they work.
The ContentPlaceHolder control is not the same thing as a Frame or even an IFrame, which have been used in the distant past to manage consistent looks and feels for Web sites and many novice Web designers still do. Primarily this is a tactic employed by a novice designer because they either do not know anything about basic programming with .NET or other web based languages such as PHP. Frames sort of went out of favor in the late 90s and now we use tables and style sheet layouts.
Old School
The idea back in the day was to say layout a frame for the header, menu or navigation that would be on every page and then a frame where the content would go. Back in the early days of the web this was a pretty good way to do things. But as pages became more sophisticated, layouts needed to be more dynamic and really holistic.
So back in the Classic ASP days, that would be the late 90s for those of you new to .NET, we started defining our layouts using include files. So we would create a separate .asp include file for the header, the navigation and then include a common layout with references to these files on each content page in the site. I even went so far as to create include files for common methods and even the Meta tag section of my pages.
Enter ASP.NET
But when ASP.NET was introduced we sort of messed up this harmony and took away the concept of include files. The first thing many of us did was substitute user controls (.ascx) for include files and did the same thing again. As we matured we started looking for ways to essentially create Skins for our sites. Various attempts were made at making this work. In my opinion none were very good.
Finally with the release of ASP.NET 2.0 we have Master Pages. While not absolutely perfect in every way they go a very long way in solving our layout issues. We can even apply them dynamically. The way they work is we can now create a consistent layout for our pages and add a control, the ContentPlaceHolder, to our page where we want to allow content pages to supply the markup. There can even be multiple ContnetPlaceHolder controls in a Master Page.
On the Content page, .aspx, there is a Content control for each ContentPlaceHolder in the Master page. It has an attribute, ContentPlaceHolderId, that references the name of the ContentPlaceHolder in the Master page, so actual order of the Content controls is not important. Everything is rendered in Design mode of Visual Studio as if it were a whole page.
So back to the Common Question
So the common question posed on the Forums.ASP.NET pages is how to place content from another URL in the ContentPlaceHolder. Which if you still want to do that, which means you are most likely page scraping or some other useless technique to get content on your site, can be done really easily. First place a Literal control in the Content control of your content page.
<asp:Content ID="Content1" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server"><asp:Literal runat=server ID="ltlContent" /></asp:Content>
asp:Content ID="Content1" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server"><asp:Literal runat=server ID="ltlContent" /></asp:Content>
asp:Literal runat=server ID="ltlContent" /></asp:Content>
asp:Content>Next we need to use the code behind and actually retrieve the foreign URL. This is done pretty easily with a WebRequest, WeResponse and StreamReader objects. First create a new WebRequest for the foreign URL. Then make the request, retrieving the response or the content of the URL to a WebResponse object. Next we need to get the stream from the WebResponse object intro a StreamReader. This is done so we can read the HTML as text.
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
If Not IsPostBack Then
Dim wr As WebRequest = WebRequest.Create("http://www.live.com")
Try
Dim mr As WebResponse = wr.GetResponse
Dim sr As New StreamReader(mr.GetResponseStream)
Dim sHTML As String = sr.ReadToEnd
sr.Close()
mr.Close()
If String.IsNullOrEmpty(sHTML) = False Then
ltlContent.Text = sHTML
End If
Catch ex As Exception
'Process the Exception Here
End Try
End If
End Sub
So now pass the text of the URL to a string using the ReadToEnd method of the StreamReader class. Because I have to put some minimal error checking in my code I check to see if I have any content to publish, and if so then I pass the string to the Text property of the Literal control on the Content page. Now the content of the URL is now displayed in our content page.
Of course you will want something a bit more sophisticated to display your content. For example you will most likely want to remove the header section from the remote URL. If it contains any references to stylesheets and JavaScript files you will want to inject them in to the Header of your actual page too. Once this is done you will most likely see the content of the remote page pretty close to how it is displayed on their site. So one of my next entries will be on injecting content and controls into the page header at run-time. But as far as publishing content inside of a ContentPlaceHolder control of a Master page, it is pretty easy, but I have to question why so many want to do this. It does not help you with Search Engine Optimization and is generally plagiarism or at least violation of copyrights too.