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# Steps to reproduce
1. Create a Xamarin Forms page;
2. Add some components to it;
3. Add any parameter to its constructor;
4. Rebuild the solution so that the Xamarin Forms Previewer works with the latest assemblies;
4. Try previewing the page.
# Expected behaviour
The page is previewed.
# Actual behaviour
A message appears saying a parameterless constructor is required.
# Supplemental info (logs, images, videos)
# Test environment (full version information)
Microsoft Visual Studio Community 2015
Version 14.0.25431.01 Update 3
Microsoft .NET Framework
Installed Version: Community
Visual Basic 2015 00322-20000-00000-AA017
Microsoft Visual Basic 2015
Visual C# 2015 00322-20000-00000-AA017
Microsoft Visual C# 2015
Visual C++ 2015 00322-20000-00000-AA017
Microsoft Visual C++ 2015
ASP.NET and Web Tools 2015.1 14.1.21111.0
ASP.NET and Web Tools 2015.1
ASP.NET Web Frameworks and Tools 2012.2 4.1.41102.0
For additional information, visit http://go.microsoft.com/fwlink/?LinkID=309563
ASP.NET Web Frameworks and Tools 2013 5.2.40314.0
For additional information, visit http://www.asp.net/
Azure App Service Tools v2.9.6 14.0.21111.0
Azure App Service Tools v2.9.6
Azure Data Lake Node 1.0
This package contains the Data Lake integration nodes for Server Explorer.
Azure Data Lake Tools for Visual Studio 2.2.2100.0
Microsoft Azure Data Lake Tools for Visual Studio
Common Azure Tools 1.8
Provides common services for use by Azure Mobile Services and Microsoft Azure Tools.
GhostDoc automatically generates XML documentation comments.
Merq 1.1.14-alpha (21c13c9)
Command Bus, Event Stream and Async Manager for Visual Studio extensions.
Microsoft .NET Core Tools (Preview 2) 14.1.21111.0
Microsoft .NET Core Tools (Preview 2)
Microsoft Azure Hive Query Language Service 2.2.2100.0
Language service for Hive query
Microsoft Azure Mobile Services Tools 1.4
Microsoft Azure Mobile Services Tools
Microsoft Azure Tools 2.9
Microsoft Azure Tools for Microsoft Visual Studio 2015 - v2.9.41104.6
Mono Debugging for Visual Studio Mono.Debugging.VisualStudio
Support for debugging Mono processes with Visual Studio.
NuGet Package Manager 3.5.0
NuGet Package Manager in Visual Studio. For more information about NuGet, visit http://docs.nuget.org/.
PreEmptive Analytics Visualizer 1.2
Microsoft Visual Studio extension to visualize aggregated summaries from the PreEmptive Analytics product.
Refactoring Essentials 1.0
Refactoring Essentials Extension Details
SQL Server Data Tools 14.0.61021.0
Microsoft SQL Server Data Tools
SQLite & SQL Server Compact Toolbox 4.6.0
SQLite & SQL Server Compact Toolbox adds scripting, import, export, rename, query execution and much more to SQL Server Compact & SQLite Data Connections.
Hosting json editor into a tool window
TypeScript tools for Visual Studio
Xamarin 184.108.40.2064 (73f58d6)
Visual Studio extension to enable development for Xamarin.iOS and Xamarin.Android.
Xamarin.Android 220.127.116.11 (9578cdc)
Visual Studio extension to enable development for Xamarin.Android.
Xamarin.iOS 10.4.0.123 (35d1ccd)
Visual Studio extension to enable development for Xamarin.iOS.
Reassigning to Previewer team to look at this.
This is expected behaviour. It is not possible to instantiate the correct class unless there's a constructor we can invoke. We can't invoke a constructor with arbitrary values as we have no generic way to create objects of the correct type.
No, it's not because it's a regression. It used to work in the version just prior to this one.
I can confirm this works in my Cycle 8 VS.
*** Bug 51228 has been marked as a duplicate of this bug. ***
Thanks so much for taking the time to file this bug @Dimitar! :) As stated previously, this is the expected behavior for the Forms Previewer. It was _not_ intended that this worked in Cycle 8, because it could cause some unintended consequences.
Think of this as similar to UWP's `DesignMode2Enabled`, allowing you to set properties and metadata for the Previewer to render. I typically use this constructor just setting up some design-time data for my data bindings.