获取当前活动 Xamarin 表单

我使用 Leadtools SDK 进行条码阅读器，当我尝试获取当前活动时，它给我 null

这是我的代码

   Stream resourceStream = new MemoryStream();
        // Droid.MainActivity activity = Forms.Context as Droid.MainActivity;
        var activity = Android.App.Application.Context as Activity;

        int resId = activity.Resources.GetIdentifier("Datamatrix", "drawable", "com.companyname.UDOSE");
     resourceStream = activity.Resources.OpenRawResource(resId);
     var leadStream = LeadStream.Factory.FromStream(resourceStream);
     await ReadBarcode(leadStream);

活动始终为空，我该如何解决这个问题？

1.定义一个全局静态Activity，在MainActivity中：

public static MainActivity Instance;
protected override void OnCreate(Bundle savedInstanceState)
    {
        TabLayoutResource = Resource.Layout.Tabbar;
        ToolbarResource = Resource.Layout.Toolbar;

        base.OnCreate(savedInstanceState);
        global::Xamarin.Forms.Forms.Init(this, savedInstanceState);       
        Instance = this;
        LoadApplication(new App());
    }

当你使用通话时MainActivity.Instance

2.使用当前活动插件,你可以参考当前活动 https://github.com/jamesmontemagno/CurrentActivityPlugin

var activity = CrossCurrentActivity.Current.Activity;

3.我建议你使用依赖服务 https://learn.microsoft.com/en-us/xamarin/xamarin-forms/app-fundamentals/dependency-service/introduction调用Droid项目中定义的方法，例如：

在共享代码中创建一个接口：

public interface IRead
{
    void Read();
}

然后在Droid项目中创建一个类：

[assembly: Dependency(typeof(AndroidRead))]
namespace Demo.Droid
{
  class AndroidRead:IRead
   {
    public async void Read()
    {
        //here is your codes
        Stream resourceStream = new MemoryStream();
        // Droid.MainActivity activity = Forms.Context as Droid.MainActivity;
        var activity = MainActivity.Instance;

        int resId = activity.Resources.GetIdentifier("Datamatrix", "drawable", "com.companyname.UDOSE");
        resourceStream = activity.Resources.OpenRawResource(resId);
        var leadStream = LeadStream.Factory.FromStream(resourceStream);
        await ReadBarcode(leadStream);
    }
  }
 }

并像这样调用 page.xaml.csDependencyService.Get<IRead>().Read();