how to fix "project.assets.json' doesn't have a target for '.NETCoreApp,Version=v3.0"?

After I changed my target framework and rebuild it is fine, then I try to publish my solution again..

then the issue comes up immediately with the following error message.

"Severity    Code    Description    Project    File    Line    Suppression State
Error        Assets file 'C:\Users\admin\source\repos\dandotnetcore\dandotnetcore\obj\project.assets.json' doesn't have a target for '.NETCoreApp,Version=v3.0'. Ensure that restore has run and that you have included 'netcoreapp3.0' in the TargetFrameworks for your project.    dandotnetcore        0   
"

the root cause of this issue is that i had create the publish profile first, then i changed the target framework. however Visual Studio never update the target framework in the publish profile.



I had to go the publish xml file and manually update it to be netcoreapp3.1

Before

<?xml version="1.0" encoding="utf-8"?>
<!--
This file is used by the publish/package process of your Web project. You can customize the behavior of this process
by editing this MSBuild file. In order to learn more about this please visit https://go.microsoft.com/fwlink/?LinkID=208121.
-->
<Project ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <PropertyGroup>
    <WebPublishMethod>FileSystem</WebPublishMethod>
    <PublishProvider>FileSystem</PublishProvider>
    <LastUsedBuildConfiguration>Release</LastUsedBuildConfiguration>
    <LastUsedPlatform>Any CPU</LastUsedPlatform>
    <SiteUrlToLaunchAfterPublish />
    <LaunchSiteAfterPublish>True</LaunchSiteAfterPublish>
    <ExcludeApp_Data>False</ExcludeApp_Data>
    <ProjectGuid>d30dbc67-142e-4bb0-a07a-5abb280b4ecc</ProjectGuid>
    <publishUrl>C:\Temp\publish</publishUrl>
    <DeleteExistingFiles>True</DeleteExistingFiles>
    <TargetFramework>netcoreapp3.0</TargetFramework>
    <SelfContained>false</SelfContained>
  </PropertyGroup>
</Project>




After

<?xml version="1.0" encoding="utf-8"?>
<!--
This file is used by the publish/package process of your Web project. You can customize the behavior of this process
by editing this MSBuild file. In order to learn more about this please visit https://go.microsoft.com/fwlink/?LinkID=208121.
-->
<Project ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <PropertyGroup>
    <WebPublishMethod>FileSystem</WebPublishMethod>
    <PublishProvider>FileSystem</PublishProvider>
    <LastUsedBuildConfiguration>Release</LastUsedBuildConfiguration>
    <LastUsedPlatform>Any CPU</LastUsedPlatform>
    <SiteUrlToLaunchAfterPublish />
    <LaunchSiteAfterPublish>True</LaunchSiteAfterPublish>
    <ExcludeApp_Data>False</ExcludeApp_Data>
    <ProjectGuid>d30dbc67-142e-4bb0-a07a-5abb280b4ecc</ProjectGuid>
    <publishUrl>C:\Temp\publish</publishUrl>
    <DeleteExistingFiles>True</DeleteExistingFiles>
    <TargetFramework>netcoreapp3.1</TargetFramework>
    <SelfContained>false</SelfContained>
  </PropertyGroup>
</Project>