How to handle a situation where activity opens multiple times due to deeplink?

There are several approaches:

1. Using flags in Intent:

   • FLAG_ACTIVITY_SINGLE_TOP: If the activity is already at the top of the stack, the onNewIntent() method will be called instead of creating a new instance.
   • FLAG_ACTIVITY_CLEAR_TOP: If the activity already exists in the stack, all activities above it will be finished, and it will be brought to the top.
   • In combination with FLAG_ACTIVITY_NEW_TASK: Often used with CLEAR_TOP for working with activities from another task.

2. Configuring launchMode in AndroidManifest.xml:

   • singleTop: Similar to FLAG_ACTIVITY_SINGLE_TOP when launching via Intent.
   • singleTask: The activity is the root of a new task; if an instance already exists in some task, it will be brought to the front, and all activities above it will be finished.
   • singleInstance: The activity exists in its own task and is the only activity in that task.

3. Checking for activity existence before launching:

   • Use ActivityManager to check the current activity stack. This approach is less preferred due to complexity and overhead.

4. Reacting to onNewIntent():

   • When using singleTop or FLAG_ACTIVITY_SINGLE_TOP, all deeplink processing logic should be implemented in the onNewIntent() method, not in onCreate(). Remember to call setIntent(intent) inside onNewIntent() to update the Intent accessible via getIntent().

Example of using launchMode="singleTop" and onNewIntent():

In AndroidManifest.xml:

<activity
    android:name=".YourDeeplinkActivity"
    android:launchMode="singleTop">
    <intent-filter>
        <action android:name="android.intent.action.VIEW" />
        <category android:name="android.intent.category.DEFAULT" />
        <category android:name="android.intent.category.BROWSABLE" />
        <data android:scheme="your_scheme"
              android:host="your_host"
              android:pathPrefix="/your_path" />
    </intent-filter>
</activity>

In the activity class YourDeeplinkActivity:

class YourDeeplinkActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_deeplink)
        // Initial processing if activity is created
        handleIntent(intent)
    }

    override fun onNewIntent(intent: Intent?) {
        super.onNewIntent(intent)
        // Important to update the Intent for getIntent()
        setIntent(intent)
        // Handle new Intent (deeplink)
        handleIntent(intent)
    }

    private fun handleIntent(intent: Intent?) {
        intent?.data?.let { uri ->
            // Logic to process the deeplink URI
            Log.d("DeeplinkActivity", "Received deeplink: $uri")
            // For example, extract parameters and navigate to the appropriate fragment
        }
    }
}

The choice of approach depends on the specific use case and desired activity stack behavior. The most common solution for deeplinks leading to an existing activity is to use launchMode="singleTop" and handle it in onNewIntent().