I have just updated all my nuget packages for my solution (dotnet core 1.1 project).
I am now getting the following warnings and I don't really know what they mean.
Update: I am still getting warnings mentioned above. My web projects warn about the Microsoft.NETCore.App package (see screenshot below) and my lib projects warn about NETStandard.Library (see screenshot above)
When trying to update Microsoft.NETCore.App in the NuGet package manager, I am getting the following error:
Hope someone can help me get rid of those warnings and setup everything it is meant to be, so I can update all my packages.
Thanks in advance!
As per answer above the working solution is to remove the following line from your csproj file.
Web App project:
<RuntimeFrameworkVersion>1.0.4</RuntimeFrameworkVersion>
Lib project:
<NetStandardImplicitPackageVersion>1.6.0</NetStandardImplicitPackageVersion>
This situation occurred to me after opening an existing solution but instead of Warnings, they were Errors.
I opened the YourAwesomeApp.csproj file and went through the "Detected package downgrade" errors one-by-one and manually changed the version of that line item from the existing version to the specified version that was shown in the error itself.
For example, if the Error says downgrade detected "SqlServer 1.0.4 -> 1.0.3" then find the line for package SqlServer and edit the version from 1.0.3 to 1.0.4.
Those errors should disappear after building the project.
The downside to this that I only had 5 errors this time but what if another person's project contained say 50 such errors. Then that person's task of manually editing those lines would be very tedious and time-consuming.
In my case neither of those properties were set in my csproj files.
I had to tell VS to update those packages via NuGet.
The warnings appeared for me after resolving the warning for explicit reference to implicit dependency .NETCore.App after moving from 1.0 to 1.1.
UPDATE 21/09/17
This also seems to affect upgrades to 2.0, the resolution is the same. Update those packages manually with NuGet. Thanks to IbrarMumtaz for pointing this out!
I was able to get rid of these warnings in my project by removing the <NetStandardImplicitPackageVersion> element from the csproj file.
There's some information in this article about implicit metapackages, which seems to be the root cause of this problem.
You might also need to update some dependencies. For example, I had to upgrade BenchmarkDotNet from 0.10.1 to 0.10.3 to get rid of a few warnings like the ones you're seeing.
I was able to fix some error like that adding NoWarn in cproj
<Project Sdk="Microsoft.NET.Sdk">
<PropertyGroup>
<NoWarn>$(NoWarn);NU1605</NoWarn>
</PropertyGroup>
...
</Project>
You may want to add it only temporarily during multiple package upgrade and remove it later.
Try using NuGet
I was getting:
error NU1605: Detected package downgrade: System.Net.NameResolution from 4.3.0 to 4.0.0. Reference the packagedirectly from the project to select a different version.
So I referenced the package directory by running (in the project folder):
dotnet add package System.Net.NameResolution
Issue:
A dependency package specified a version constraint on a higher version of a package than restore ultimately resolved. That is, because of the "nearest wins" rule when resolving packages, a nearer package in the graph may have overridden a distant package.
Solution:
Add a direct reference to the project for the higher version of the package that you want to use.
This generally happens because the item you are attempting to install requires a more recent version of a sub-dependency than you have already included in your project.
The solution is to update or delete the existing dependency that is in your project prior to installing the package.
Example:
Detected package downgrade: Newtonsoft.Json from 9.0.0 to 8.0.0.
This means you have Newtonsoft.Json 8.0.0 already listed as a dependency in your project, but the package you are trying to install requires at least version 9.0.0 as a dependency.
This is because Visual studio won't automatically upgrade this dependency as you've specified an explicit version for your project. You can either upgrade the dependency in your project to the minimum required version or remove it from your project, and let the package you're installing handle it.
To resolve this, in our example above, this would mean finding 'Newtonsoft.Json 8.0.0' and upgrading it to version '9.0.0' or simply removing it from your project prior to installing your package.
Try removing:
<IsPackable>false</IsPackable>
from your project file - this is what worked for me!
If you are still left with NU1605 Error code you can ignore it by adding the following to your project file:
<PropertyGroup>
<NoWarn>NU1605</NoWarn>
</PropertyGroup>
Manually removing the nuget packages dependencies from the project and Install-Package for each of them fixed the problem in my case.
In my case, this error was not related to .NET Core but to .NET Standard.
I had two libraries A, and B. Library A depended on some nuget package X, and library B depended on A. Once I upgraded X to a new version, somehow it started depending on a new version of NETStandard.Library nuget package (from 2.0.2 to 2.0.3), which broke the build of B with the error Detected package downgrade: NETStandard.Library from 2.0.3 to 2.0.2. Reference the package directly from the project to select a different version.
Once I added the NETStandard.Library nuget package as a dependency to B (obviously targetting the latest version 2.0.3), the error went away, even if a new warning appeared:
/usr/local/share/dotnet/sdk/2.1.403/Sdks/Microsoft.NET.Sdk/targets/Microsoft.NET.Sdk.DefaultItems.targets(5,5): Warning NETSDK1023: A PackageReference for 'NETStandard.Library' was included in your project. This package is implicitly referenced by the .NET SDK and you do not typically need to reference it from your project. For more information, see https://aka.ms/sdkimplicitrefs (NETSDK1023) (GWallet.Frontend.XF)
I was trying to upgrade Microsoft.AspNetcore.MVC to Version 2+. The solution for me was to upgrade all of the other dependencies first to 2+, then finally upgrade .MVC.
I could solve the problem by downloading earlier version of the package causing the problem, that seems to be caused by depending on a .NET Standard version that's not installed, this also should be solved by updating Visual Studio.
I just recently came across this issue and updating the NuGet packages was what worked for me.
I solved this issue thanks to this answer. Basically, just add the following line inside the <PropertyGroup> tags in your .csproj file:
<TargetLatestRuntimePatch>true</TargetLatestRuntimePatch>
来源：https://stackoverflow.com/questions/42709533/detected-package-downgrade-warning-dotnet-core-vs-2017