无法从程序集'Xamarin.Forms.Core'加载类型'Xamarin.Forms.Preserve属性'

我刚刚继承了旧的Xamarin Forms应用程序，我试图升级所有程序包。应用程序最初运行良好，但由于升级到所有软件包的最新版本，我现在得到一个崩溃调用Xamarin.Forms.Forms.Init(this, bundle);：无法从程序集'Xamarin.Forms.Core'加载类型'Xamarin.Forms.Preserve属性'

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>

来源

2016-05-16 Mick Byrne

我看到你正在尝试使用Forms 2.3.0.38-pre2 packkage。确保您还将Forms.Maps包更新为相应的预先版本！ –