无法从程序集“Xamarin.Forms.Core”加载类型“Xamarin.Forms.Preserve Attribute”

Question

我刚刚继承了一个旧的 Xamarin Forms 应用程序，我正在尝试升级所有包。应用程序最初运行良好，但自从升级到所有软件包的最新版本后，我现在收到崩溃调用Xamarin.Forms.Forms.Init(this, bundle);：

Could not load type 'Xamarin.Forms.PreserveAttribute' from assembly 'Xamarin.Forms.Core, Version=2.0.0.0, Culture=neutral, PublicKeyToken=null'.

这是我的 packages.config 文件内容：

<?xml version="1.0" encoding="utf-8"?>
<packages>
  <package id="ExifLib.PCL" version="1.0.1" targetFramework="MonoAndroid50" />
  <package id="Microsoft.Bcl" version="1.1.10" targetFramework="MonoAndroid50" />
  <package id="Microsoft.Bcl.Build" version="1.0.21" targetFramework="MonoAndroid50" />
  <package id="Microsoft.Net.Http" version="2.2.29" targetFramework="MonoAndroid50" />
  <package id="Newtonsoft.Json" version="8.0.3" targetFramework="MonoAndroid50" />
  <package id="Xamarin.Android.Support.Animated.Vector.Drawable" version="23.3.0" targetFramework="MonoAndroid50" />
  <package id="Xamarin.Android.Support.Design" version="23.3.0" targetFramework="MonoAndroid50" />
  <package id="Xamarin.Android.Support.v4" version="23.3.0" targetFramework="MonoAndroid50" />
  <package id="Xamarin.Android.Support.v7.AppCompat" version="23.3.0" targetFramework="MonoAndroid50" />
  <package id="Xamarin.Android.Support.v7.CardView" version="23.3.0" targetFramework="MonoAndroid50" />
  <package id="Xamarin.Android.Support.v7.MediaRouter" version="23.3.0" targetFramework="MonoAndroid50" />
  <package id="Xamarin.Android.Support.v7.RecyclerView" version="23.3.0" targetFramework="MonoAndroid50" />
  <package id="Xamarin.Android.Support.Vector.Drawable" version="23.3.0" targetFramework="MonoAndroid50" />
  <package id="Xamarin.Forms" version="2.3.0.38-pre2" targetFramework="MonoAndroid50" />
  <package id="Xamarin.Forms.Labs" version="1.2.1-pre2" targetFramework="MonoAndroid44" />
  <package id="Xamarin.Forms.Maps" version="2.2.0.31" targetFramework="MonoAndroid50" />
  <package id="Xamarin.GooglePlayServices.Base" version="29.0.0.1" targetFramework="MonoAndroid50" />
  <package id="Xamarin.GooglePlayServices.Basement" version="29.0.0.1" targetFramework="MonoAndroid50" />
  <package id="Xamarin.GooglePlayServices.Maps" version="29.0.0.1" targetFramework="MonoAndroid50" />
  <package id="Xamarin.Insights" version="1.12.3" targetFramework="MonoAndroid50" />
</packages>

Answer 1

我关闭了 Xamarin Studio 并清除了 obj 和 bin 文件夹，然后再次启动了 Xamarin Studio，一切正常