Xamarin.Essentials.FileResult 成员：(null) - 媒体选择器

如何解决Xamarin.Essentials.FileResult 成员：(null) - 媒体选择器

我是 xamarin 的新手。当我尝试从图库中选择照片时，在按钮 Clicked_Event 时出现以下错误。 错误：

System.TypeLoadException: '无法加载字段'App2.Views.NewDoctor+d__5:5__1' (5) 的类型，原因是：无法使用来自 typeref 的标记 010000a5 解析类型（预期类 'Xamarin.Essentials. FileResult' 在程序集中“Xamarin.Essentials，版本=1.0.0.0，文化=中性，PublicKeyToken=null”）程序集：Xamarin.Essentials，版本=1.0.0.0，文化=中性，PublicKeyToken=null 类型：Xamarin.Essentials.FileResult成员：（空）'

按钮代码：

async void Button_Clicked(System.Object sender,System.EventArgs e)
{
    var result = await MediaPicker.PickPhotoAsync(new MediaPickerOptions
        {
            Title="Please Pick a photo"
        }
    );
    if (result != null)
    {
        var stream = await result.OpenReadAsync();
        resultimage.source = ImageSource.FromStream(() => stream);
    }
}

MainActivity.cs

[Activity(Label = "App2",Icon = "@mipmap/icon",Screenorientation =Android.Content.PM.Screenorientation.Portrait,Theme = "@style/MainTheme",MainLauncher = false,ConfigurationChanges = ConfigChanges.ScreenSize | ConfigChanges.Orientation)]
public class MainActivity : global::Xamarin.Forms.Platform.Android.FormsAppCompatActivity
{
    protected override void OnCreate(Bundle savedInstanceState)
    {
        TabLayoutResource = Resource.Layout.Tabbar;
        ToolbarResource = Resource.Layout.Toolbar;

        base.OnCreate(savedInstanceState);
        global::Xamarin.Forms.Forms.Init(this,savedInstanceState);
        Plugin.CurrentActivity.CrossCurrentActivity.Current.Init(this,savedInstanceState);
        LoadApplication(new App());

    }

    public override void OnRequestPermissionsResult(int requestCode,string[] permissions,[GeneratedEnum] Android.Content.PM.Permission[] grantResults)
    {
        PermissionsImplementation.Current.OnRequestPermissionsResult(requestCode,permissions,grantResults);
        base.OnRequestPermissionsResult(requestCode,grantResults);
    }
}

}

我正在使用以下软件包：

AndroidMenifest.xml

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.CAMERA" />