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Showing posts from February, 2013

Prevent multiple postbacks in SharePoint 2013

The scenario:  Disabled the button after user’s click event. Prevent user from clicking it several times.

The problem: If the button is disabled, the server side event handler is not fired.

The solution: Set the property UseSubmitBehavior to false.

Explanations

Here is the working code of how to have disabled button after it is clicked:


<asp:ButtonID="Button1"runat="server"Text="Do Postback"UseSubmitBehavior="false"OnClick="Button1_Click"OnClientClick="Validate(this)"/>

function Validate(thisObj)        {            thisObj.disabled = true; returntrue;        }

If you don't set the property UseSubmitBehavior your code in the handler Button1_Click won’t fire. I spend several hours in debugging it. Hope this save time to somebody.



SharePoint and List Joins with CAML

This came to me as an issue when I started migrating one project from SharePoint 2010 to SharePoint 2013. The code uses LINQ to SharePoint and it was not written in a clever way. We decide to use CAML queries and optimize the code.

The scenario: Create gridview that gathers information from three(or more) lists.
The problem: How to create the CAML query joins and projected fields correctly.

Explanation:

Option 1: Get generated CAML query from LINQ to SharePoint code
This doesn’t work. I wrote the LINQ to SharePoint code connected the three lists. When I executed the code the following error was thrown – “The query uses unsupported elements, such as references to more than one list, or the projection of a complete entity by using EntityRef/EntitySet.Here is some explanation about it and why this can’t be used.

Option 2: Write the query yourself
I found this article in MSDN. Read it !
The second part in it is exactly my scenario. But it takes me a lot of time to understand how exactly to …

Using SharePoint Attachments' controls with elevated security

The scenario:  Create custom forms for Add/Edit/Delete items to a list which is not accessible by the regular users. The forms should support working with attachments.

The problem: The default SharePoint controls don’t work if the current user doesn’t have access to the list items.

The solution:Use custom code for generating the SharePoint default HTML so the out-of-the-box javascript works correct.

Explanations: 
The scenario occurs when some list need to be hidden form the users. The list has broken security inheritance and users can't navigate directly to it.

Working with its fields requires crating web warts or application pages with appropriate controls on them and server-side code running under elevated privileges. The issue here is that the OOTB (out-of-the-box) controls for Attachments don't work if the user doesn’t have access to the related list item.

The OOTB controls are: AttachmentsField, AttachmentUpload, AttachmentButton. There is a lot of code how to use them so h…

ClientPeoplePicker in SharePoint 2013

Start using SharePoint 2013 I noticed that the way for selecting people or groups is changed.
The new way is simple – just ‘Enter name or email address’ without any icons for ‘Check Names’ or ‘Browse’. I guess that the PeoplePicker is changed but NO. PeoplePicker sitll has the same functionality as before.
There is a new control called ClientPeoplePicker.

How to use it:
1.Add this references

<%@RegisterTagPrefix="wssawc"Namespace="Microsoft.SharePoint.WebControls"Assembly="Microsoft.SharePoint, Version=15.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c"%>
2.Add the following control declaration


      <wssawc:ClientPeoplePicker Required="true" ValidationEnabled="true" ID="peoplePicker" runat="server" InitialHelpText="<%$Resources:wss,aclinv_PickerIntialHelperText%>" VisibleSuggestions="3" Rows="1" AllowMultipleEntities="false" CssClass