问题
I am running Visual Studio 2012 plus Xamarin.iOS with the latest version of each. I have Portable Class Libraries in which I want to select the latest "Xamarin.iOS" release as a build target (instead of MonoTouch). In Visual Studio I open up the Project's Properties, select the Library tab, and click on Change under Target Frameworks. However, I am unable to modify any of the checkboxes. Any checkbox I change instantly closes the "Change Target Frameworks" dialog. If I change one of the dropdowns (for example, change from .NET 4.0+ to 4.5) then when I go to click OK the changes do not get reflected in the Target Frameworks list.
Anyone have any idea how to resolve this issue?
回答1:
I was able to resolve this by changing the TargetFrameworkProfile in the XML of the csproj file. I was on Profile104 which is no longer supported, so I manually removed this and left this blank in the XML, and then was able to re-add the profile targets (after using the dialog it put me on Profile136).
回答2:
I've encountered a similar problem , while trying to add MvvmCross Nuget Package. I've to change PCL profile to 259 , it didn't allow me ( Xamarin Studio on iOS) , Ok and Cancel buttons are not present.
- I opened the .csproj file in TextEditor.
- Removed the PCL profile information. Reopened the project.It gave me build error.
- So added following string manually Profile259
It Started working.Hope this information helps.
来源：https://stackoverflow.com/questions/20009886/unable-to-alter-pcl-library-target-frameworks