MainActivity.kt

import android.content.Intent
import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.util.Log

private const val tag = "2ndShare"

/**
 * 1) Clear all the apps
 * 2) Go to Google Photos, share image to this app
 * 3) Do nothing in this app, switch to Google Photos (…and NOT by navigating back!)
 * 4) Share some other image to this app
 *
 * Change activity mode in manifest to observe what's going on:
 * launchMode = standard: ¯\_(ツ)_/¯
 *   1st Share -> onCreate,onResume
 *   2nd Share -> onResume
 *
 *  launchMode = singleTask: OK
 *   1st Share -> onCreate,onResume
 *   2nd Share -> onNewIntent,onResume
 *
 *  launchMode = singleTop: OK
 *   1st Share -> onCreate,onResume
 *   2nd Share -> onNewIntent,onResume
 *
 *  launchMode = singleInstance: OK
 *   1st Share -> onCreate,onResume
 *   2nd Share -> onNewIntent,onResume
 */
class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        Log.d(tag, "onCreate ${intent.describe()}")
    }

    override fun onResume() {
        super.onResume()
        Log.d(tag, "onResume ${intent.describe()}")
    }

    override fun onNewIntent(intent: Intent?) {
        super.onNewIntent(intent)
        Log.d(tag, "onNewIntent ${intent.describe()}")
        setIntent(intent)
    }
}

fun Intent?.describe() : String {
    if (this == null) return "null intent"

    val extras = extras ?: return "empty intent"

    return extras[Intent.EXTRA_STREAM]?.toString() ?: "no stream"
}

for the standard launch mode, the intent never changes unless you kill the app or finish activity with a result