我的应用程序上的按钮应该是边缘圆形，使按钮像椭圆形状。更新我的xamairin表单并添加几个dll之后，即使我在内容页面本身设置了按钮的边框半径，按钮外观也总是正方形。似乎这是造型的唯一问题，因为app.xaml页面中设置的背景颜色仍然有效。
我有这些警告信息：
Severity Code Description Project File Line Suppression State
Warning Could not resolve this reference. Could not locate the assembly "Mono.Android". Check to make sure the assembly exists on disk. If this reference is required by your code, you may get compilation errors. CompNam.MobileApp
Warning The referenced component 'Mono.Android' could not be found. CompNam.MobileApp
Warning The $(TargetFrameworkVersion) for Xamarin.Forms.Platform.Android.dll (vv8.0) is greater than the $(TargetFrameworkVersion) for your project (v7.1). You need to increase the $(TargetFrameworkVersion) for your project. CompNam.MobileApp.Android C:\Users\User\Short\CompNamPortalApp\CompNam.MobileApp\CompNam.MobileApp.Android\CompNam.MobileApp.Android.csproj
Warning The $(TargetFrameworkVersion) for FormsViewGroup.dll (vv8.0) is greater than the $(TargetFrameworkVersion) for your project (v7.1). You need to increase the $(TargetFrameworkVersion) for your project. CompNam.MobileApp.Android C:\Users\User\Short\CompNamPortalApp\CompNam.MobileApp\CompNam.MobileApp.Android\CompNam.MobileApp.Android.csproj
Warning The $(TargetFrameworkVersion) for Xamarin.Forms.Platform.dll (vv8.0) is greater than the $(TargetFrameworkVersion) for your project (v7.1). You need to increase the $(TargetFrameworkVersion) for your project. CompNam.MobileApp.Android C:\Users\User\Short\CompNamPortalApp\CompNam.MobileApp\CompNam.MobileApp.Android\CompNam.MobileApp.Android.csproj
Warning The $(TargetFrameworkVersion) for Xamarin.Android.Support.Annotations.dll (vv8.0) is greater than the $(TargetFrameworkVersion) for your project (v7.1). You need to increase the $(TargetFrameworkVersion) for your project. CompNam.MobileApp.Android C:\Users\User\Short\CompNamPortalApp\CompNam.MobileApp\CompNam.MobileApp.Android\CompNam.MobileApp.Android.csproj
这些消息是否会影响按钮的外观？