Xamarin形成android语音识别ActivityNotFoundException

Question

我一直试图在我的安卓应用程序中添加语音到文本，但我一直在使用"Android.Content.ActivityNotFoundAcception“。

我使用的是Android5.0(棒棒糖)模拟器，因为我的电脑不能启动任何其他模拟器。

接口：

    public interface ISpeech
    {
        Task<string> SpeechToTextAsync();
    }

创建意图和开始活动：

    // When i remove Java.Lang.Object it gives Java.Lang.NullPointer Exception 
    public class AndroidSpeech : Java.Lang.Object, ISpeech
    {
        public static AutoResetEvent autoEvent = new AutoResetEvent(false);
        private Intent voiceIntent;
        public static readonly int speech = 10; // requestCode
        public static string speechResults;
        public async Task<string> SpeechToTextAsync()
        {
            var context = Forms.Context;
            var activity = (Activity)context;
            voiceIntent = new Intent(RecognizerIntent.ActionRecognizeSpeech);
            voiceIntent.PutExtra(RecognizerIntent.ExtraLanguageModel, RecognizerIntent.LanguageModelFreeForm);
            voiceIntent.PutExtra(RecognizerIntent.ExtraPrompt, "Speak");
            voiceIntent.PutExtra(RecognizerIntent.ExtraSpeechInputCompleteSilenceLengthMillis, 1500);
            voiceIntent.PutExtra(RecognizerIntent.ExtraSpeechInputPossiblyCompleteSilenceLengthMillis, 1500);
            voiceIntent.PutExtra(RecognizerIntent.ExtraSpeechInputMinimumLengthMillis, 15000);
            voiceIntent.PutExtra(RecognizerIntent.ExtraMaxResults, 1);
            voiceIntent.PutExtra(RecognizerIntent.ExtraLanguage, Java.Util.Locale.Default);
            autoEvent.Reset();
            activity.StartActivityForResult(voiceIntent, speech);
            await Task.Run(() => { autoEvent.WaitOne(new TimeSpan(0, 0, 3)); });
            return speechResults;
        }
    }

在获得OnActivityResult之前，它可以正常工作，这里会抛出异常

主要活动：

protected override void OnActivityResult(int requestCode, Result resultCode, Intent data)
{
    if (requestCode == AndroidSpeech.speech)
    {
       // resultCode returns Result.Canceled
       if (resultCode == Result.Ok) // here it throws ActivityNotFoundException
       {
          var speech = data.GetStringArrayListExtra(RecognizerIntent.ExtraResults);
          AndroidSpeech.speechResults = speech[0];
       }
       AndroidSpeech.autoEvent.Set();
    }
    base.OnActivityResult(requestCode, resultCode, data);
}

在按钮上调用函数单击：

 private async void OnStartBtnClick(object sender, EventArgs args)
 {
      string speechResults = await DependencyService.Get<ISpeech().SpeechToTextAsync();
      Lbl.Text = speechResults;
 }

我也试过：

    [Activity]
    public class AndroidSpeech : Activity, ISpeech
    {
        // this gives Java.Lang.NullPointer Exception 
    }

我也尝试创建我自己的RecognitionListener，但是我无法返回结果。

Answer 1

如果您获得"Android.Content.ActivityNotFoundAcception".是因为xamarin Dependencyservice只有on活动，而AndroidSpeech不是活动，则不使用StartActivityForResult directly.Solution is获取对当前活动的引用，为此，我们将添加一个名为Plugin.Current activity的nuget。

可以在应用程序类中添加活动回调，因此我的应用程序类如下所示

  [Application]
public class MainApplication : Application, Application.IActivityLifecycleCallbacks
{
    public MainApplication(IntPtr handle, JniHandleOwnership transer)
      : base(handle, transer)
    {
    }

    public override void OnCreate()
    {
        base.OnCreate();
        RegisterActivityLifecycleCallbacks(this);
        //A great place to initialize Xamarin.Insights and Dependency Services!
    }

    public override void OnTerminate()
    {
        base.OnTerminate();
        UnregisterActivityLifecycleCallbacks(this);
    }

    public void OnActivityCreated(Activity activity, Bundle savedInstanceState)
    {
        CrossCurrentActivity.Current.Activity = activity;
    }

    public void OnActivityDestroyed(Activity activity)
    {
    }

    public void OnActivityPaused(Activity activity)
    {
    }

    public void OnActivityResumed(Activity activity)
    {
        CrossCurrentActivity.Current.Activity = activity;
    }

    public void OnActivitySaveInstanceState(Activity activity, Bundle outState)
    {
    }

    public void OnActivityStarted(Activity activity)
    {
        CrossCurrentActivity.Current.Activity = activity;
    }

    public void OnActivityStopped(Activity activity)
    {
    }
}

在AndroidSpeech类中，您将得到对当前活动的引用，如下所示

_activity = CrossCurrentActivity.Current.Activity;

然后您可以在StartActivityForResult中调用AndroidSpeech

有关于如何一步一步地实现语音到文本的博客，你可以参考它。https://medium.com/@dev.aritradas/xamarin-forms-speech-recognition-c16f07cdf164

这是演示。https://github.com/dev-aritra/XFSpeech

更新这是在运行GIF。

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