Broadcast Receiver not displaying Toast via OnReceive method in Xamarin Android

问题

Am trying to implement a Broadcast receiver class in my project, I have a receiver that extends class BroadcastReceiver and I intend to check if the Broadcast was received via a button click, The OnReceive method has a Toast code inside that should display the nessage Intent Detected if the broadcast was succesfully sent. My code looks like this...

 class FlashActivity : AppCompatActivity
    {
           protected override void OnCreate(Bundle savedInstanceState)
           {
         //Button definition
            Button button1 = this.FindViewById<Button>(Resource.Id.button1);
        //Clicking on this button should send the Broadcast message
            button1.Click += broadCastIntent;
           }
      //Method to send broadcast message on button click
       private void broadCastIntent(object sender,EventArgs e)
        {
            Intent intent = new Intent();
            intent.SetAction("com.Java_Tutorial.CUSTOM_INTENT");
            SendBroadcast(intent);
        }
       //BroadCast Receiver class Implementation

       [BroadcastReceiver(Name="com.Java_Tutorial.CUSTOM_INTENT")]
        public class MyReceiver: BroadcastReceiver
        {
            public override void OnReceive(Context context, Intent intent)
            {
           //Acknowledge message was received via a Toast
                Toast.MakeText(context, "Intent Detected.", ToastLength.Long).Show();
            }
        }
    }

The Receiver code section of my Manifest.xml file looks like this

<application android:allowBackup="true" android:icon="@mipmap/ic_launcher" android:label="@string/app_name" android:roundIcon="@mipmap/ic_launcher_round" android:supportsRtl="true" android:theme="@style/AppTheme">
        <receiver android:name="MyReceiver">
            <intent-filter>
                <action android:name="com.Java_Tutorial.CUSTOM_INTENT"></action>
            </intent-filter>
        </receiver>
    </application>

When i click the button, No Toast is displayed please help...

回答1:

When i click the button, No Toast is displayed

You do not register your BroadcastReceiver in your Activity.

Please register it like following code.

  [Activity(Label = "@string/app_name", Theme = "@style/AppTheme", MainLauncher = true)]
    public class MainActivity : AppCompatActivity
    {
        MyReceiver receiver;
        protected override void OnCreate(Bundle savedInstanceState)
        {
            base.OnCreate(savedInstanceState);
            Xamarin.Essentials.Platform.Init(this, savedInstanceState);
            // Set our view from the "main" layout resource
            SetContentView(Resource.Layout.activity_main);
            Button button1 = this.FindViewById<Button>(Resource.Id.button1);

             receiver = new  MyReceiver();
            //Clicking on this button should send the Broadcast message
            button1.Click += broadCastIntent; ;
          
        }

      

        private void broadCastIntent(object sender, System.EventArgs e)
        {
            Intent intent = new Intent();
            intent.SetAction("com.Java_Tutorial.CUSTOM_INTENT");
            SendBroadcast(intent);

           
        }
        //BroadCast Receiver class Implementation
        protected override void OnResume()
        {
            base.OnResume();
            RegisterReceiver(receiver, new IntentFilter("com.Java_Tutorial.CUSTOM_INTENT"));
            // Code omitted for clarity
        }

        protected override void OnPause()
        {
            UnregisterReceiver(receiver);
            // Code omitted for clarity
            base.OnPause();
        }

        public override void OnRequestPermissionsResult(int requestCode, string[] permissions, [GeneratedEnum] Android.Content.PM.Permission[] grantResults)
        {
            Xamarin.Essentials.Platform.OnRequestPermissionsResult(requestCode, permissions, grantResults);

            base.OnRequestPermissionsResult(requestCode, permissions, grantResults);
        }
    }

    
    [BroadcastReceiver(Name = "com.Java_Tutorial.CUSTOM_INTENT")]
    public class MyReceiver : BroadcastReceiver
    {
        public override void OnReceive(Context context, Intent intent)
        {
            //Acknowledge message was received via a Toast
            Toast.MakeText(context, "Intent Detected.", ToastLength.Long).Show();
        }
    }
}

Here is running GIF.

Here is a helpful article about broadcast. You cna refer to it.

https://docs.microsoft.com/en-us/xamarin/android/app-fundamentals/broadcast-receivers#context-registering-a-broadcast-receiver

Update

tried to find a post where you detect if flashlight is already on via a broadcast and then toggle switch accordingly in my app

Android OS do not provide system broadcast for flashlight. But we can check the flashlight's status.If the flashlight's status is open, we can send an broadcast, then our broadcastReceiver to get it.

// note: camera come from:  private Android.Hardware.Camera camera=Android.Hardware.Camera.Open();

 if (camera.GetParameters().FlashMode.Equals(Android.Hardware.Camera.Parameters.FlashModeOff))
            {
                switchOn = false;
            }
            else if (camera.GetParameters().FlashMode.Equals(Android.Hardware.Camera.Parameters.FlashModeTorch))
            {
                switchOn = true;
                Intent intent = new Intent();
                intent.SetAction("com.Java_Tutorial.CUSTOM_INTENT");
                SendBroadcast(intent);
            }

回答2:

You need to add an IntentFilter attribute

[BroadcastReceiver(Enabled = true)]
[IntentFilter(new[] { "com.Java_Tutorial.CUSTOM_INTENT" })]
public class MyReceiver: BroadcastReceiver
{
    public override void OnReceive(Context context, Intent intent)
     {
         //Acknowledge message was received via a Toast
         Toast.MakeText(context, "Intent Detected.", ToastLength.Long).Show();
     }
}

来源：https://stackoverflow.com/questions/64341648/broadcast-receiver-not-displaying-toast-via-onreceive-method-in-xamarin-android