Duplicate Web Parts appear when you activate and deactivate a feature

In this post Chris O’Brien explain in detail why sometimes duplicates web parts appear:

http://www.sharepointnutsandbolts.com/2009/02/extending-web-part-framework-part-2.html

Issues and resolutions

I think that many of the challenges we faced are worth sharing as they came about through general web part development, rather than anything specific to what we did. Before I detail the actual gotchas, take note of some key development characteristics of our project:

  • Solutions and features used to deploy artifacts such as page layouts, content types etc.
  • Kivati Studio used for some other deployment aspects
  • Main functionality implemented in user controls – web parts were effectively thin wrappers around the .ascx files using LoadControl()
  • Web parts which are ‘mandatory’ are added to pages using the AllUsersWebPart element in a feature (though as the points probably illustrate, we looked at numerous ways of dealing with this)

Finding #1 – web parts outside of web part zones cannot be edited

The reason we wanted to have web parts outside of zones (perfectly possible by dragging a web part directly into page layout markup in SharePoint Designer) is for ‘fixed’ page modules which could not be removed by the content author. When we placed web parts outside of web part zones, we found the web parts would run fine in presentation mode but unfortunately cannot be edited (e.g. to edit web part properties) – the edit menu for the web part simply does not appear. I speculate this is because it is web part zones which are linked to web part storage, and thus web part properties cannot be persisted without a zone (the values in the markup will always be used). Hence, if you want editable web parts, you need web part zones.

Resolution – ensure all web parts (even ones which cannot be removed) live in a web part zone.

Finding #2 – embedding web parts into user control markup appears to be problematic

We tested various permutations of using web parts in/out of web part zones, and also with the HTML markup directly in the page layout .aspx or in a child .ascx file. After establishing that web part zones were required, we also found that whether the markup was in the .aspx or .ascx appeared to make a difference. This was unexpected, but the net effect seems to be that if you insert the web part markup into a web part zone which is in a user control rather than directly in the page layout .aspx (i.e. by refactoring the HTML markup for the web part zone and it’s contents into a user control), again the edit menu will not display. I’m not sure why this is, but it could be related to the page execution lifecycle.

Resolution – accept that if web part zones will have web parts added to them at design-time by markup, the web part zone declaration cannot be in a user control.

Finding #3 – when using AllUsersWebPart element, duplicate web parts appear if the feature containing your page layouts is reactivated

Having decided our ‘fixed’ web parts would be added to pages using the AllUsersWebPart feature element (N.B. using this approach, ‘default’ web parts are associated with page layouts in the feature which deploys them. Web part zones are left empty on the page layout, and SharePoint provisions the web part into the zone at the time of creating a page from the layout). The issue we had with this is that all the web parts in all the zones in existing pages would be duplicated if the page layout feature was reactivated – this is because this XML is used both when the feature is activated (in the same way as say, provisioning for content types happens on activation) but also when new pages are created from a page layout.

Resolution – write a script (a Kivati task in our case) to remove duplicate web parts across all sites

[UPDATE – Waldek has an elegant solution to this problem in ‘Preventing provisioning duplicate Web Part instances on Feature reactivation’, as well as sample code similar to what we wrote for our script. DOH!]

Finding #4 – duplicate web parts can also appear when the page layout is customized (ghosted)

I’m not exactly clear on the reasons why customized files would ever cause duplicate web parts to appear, but that’s certainly what we seemed to find. What happened is that we would deploy our master pages/page layouts using a feature to our QA environment, but immediately these files would be provisioned in that site as customized (i.e. the content in the content database), instead of being uncustomized and referenced on the filesystem. After further investigation, we traced the cause of this unexpected behaviour to the use of these attributes SPD adds to page layouts:

meta:progid=”SharePoint.WebPartPage.Document” meta:webpartpageexpansion=”full”

Resolution – ensure the version of the file does not contain these attributes. We actually switched to running uncustomized master page/page layouts even in our development farm. This means that we deployed the files using a feature and thereafter never opened them in SPD (editing only the source-controlled feature file instead).

Finding #5 – avoid setting default properties in the web part definition file (.webpart)

A final lesson we learnt is that, when working with web parts it’s often better to avoid using the .webpart definition file extensively for setting default property values. There’s nothing wrong with the mechanism – effectively these values are read whenever the web part is provisioned on a page, and your instance will set it’s properties to these values. The problem, of course, is when you realize a property value you defined in the .webpart file needs to be updated because something changed. What happens to all the existing instances on pages around your site? As you might guess, the answer is nothing – unless you take steps to update those also, which generally means writing some kind of script to use SPLimitedWebPartManager. This can be pretty inconvenient when all you wanted to do was quickly change a default value.

Resolution – consider ensuring .webpart files are stripped to the bare minimum (assembly name etc.) and configuration comes from somewhere else. We typically rolled these config items into our use of the Config Store.

Summary

We ran into a few unexpected gotchas when building on the web part framework, but steps can be taken to minimise their impact. Hope you find these useful if you do web part development. Special thanks to Karoly Szalkary for helping to refresh my memory on some of these!

Where the data gets store in a web part?

Post: http://www.novolocus.com/2009/02/23/storing-data-within-web-parts/

The data is store using web part properties, and all the information gets store as part of the page as unstructured information.

Streaming and buffering in SharePoint 2010

The best single link is a fairly new Technet article on caching and performance planning with SharePoint 2010: http://technet.microsoft.com/en-us/library/ee424404(office.14).aspx. Summary: performance can be tuned through disk-based BLOB caching and bit rate throttling

Bitrate throttling configuration walkthrough: http://learn.iis.net/page.aspx/148/bit-rate-throttling-configuration-walkthrough/. Summary: detailed guide from the IIS team

More direction on where we’re going with streaming (the out-of the-box media web part uses buffering, NOT streaming. Streaming is enabled via IIS media services): http://misfitgeek.com/blog/iis-media-services-3-0/. Summary: good overview of IIS Media Services 3.0

And finally, Silverlight 4 capabilities, including multicasting. Currently SL4 is in beta: http://scorbs.com/2009/11/19/pdc-session-silverlight-4-beta-overview/ http://blogs.msdn.com/ncl/archive/2009/11/18/udp-multicast-in-silverlight-4.aspx