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I keep reading you can do C# on SPO (sandboxed solution). I make a small webpart that says hi, it deploys to my development site with no errors, but it doesnt look like it installs the feature. What gives ? 
I then find an article that you can't do sandboxed soultions <a href="https://blogs.technet.microsoft.com/marios_mo_betta_blog/2016/08/02/sharepoint-online-sandboxed-solutions-disabled/" rel="ugc">https://blogs.technet.microsoft.com/marios_mo_betta_blog/2016/08/02/sharepoint-online-sandboxed-solutions-disabled/</a> 
In this article in mentions how to do it anyway (I think ?) <a href="https://support.microsoft.com/en-us/help/3183084/remove-the-assembly-reference-from-your-sandbox-solution-created-in-vi" rel="ugc">https://support.microsoft.com/en-us/help/3183084/remove-the-assembly-reference-from-your-sandbox-solution-created-in-vi</a> 
Can someone tell me if you can write a C# visual web part for SPO ? Definitavely ? I have to present this to management and I want to be correct.
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I keep reading you can do C# on SPO (sandboxed solution). I make a small webpart that says hi, it deploys to my development site with no errors, but it doesnt look like it installs the feature. What gives ?
I then find an article that you can't do sandboxed soultions https://blogs.technet.microsoft.com/marios_mo_betta_blog/2016/08/02/sharepoint-online-sandboxed-solutions-disabled/ (https://blogs.technet.microsoft.com/marios_mo_betta_blog/2016/08/02/sharepoint-online-sandboxed-solutions-disabled/)
In this article in mentions how to do it anyway (I think ?) https://support.microsoft.com/en-us/help/3183084/remove-the-assembly-reference-from-your-sandbox-solution-created-in-vi (https://support.microsoft.com/en-us/help/3183084/remove-the-assembly-reference-from-your-sandbox-solution-created-in-vi)
Can someone tell me if you can write a C# visual web part for SPO ? Definitavely ? I have to present this to management and I want to be correct.

Can you do C# in SharePoint Online

Microsoft Sharepoint is a software platform and family of software products used for collaboration and web publishing combined. These capabilities include developing web sites, portals, intranets, content management systems, search engines, wikis, blogs, and other tools for business intelligence and collaboration. SharePoint has a Microsoft Office-like interface, and it is closely integrated with the Office suite.

Microsoft SharePoint

C# is an object-oriented programming language created in conjunction with Microsoft’s .NET framework. Compilation is usually done into the Microsoft Intermediate Language (MSIL), which is then JIT-compiled to native code (and cached) during execution in the Common Language Runtime (CLR).