Intents

What is an Intent?

An Intent is a messaging object used to request an action from another component. It's the primary mechanism for communication between Android components — Activities, Services, and Broadcast Receivers.

Explicit Intents

Explicit intents specify exactly which component to start:

class HomeActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_home)

        findViewById<Button>(R.id.btnDetail).setOnClickListener {
            // Explicit intent — target is known
            val intent = Intent(this, DetailActivity::class.java)
            intent.putExtra("itemId", "12345")
            intent.putExtra("title", "Android Fundamentals")
            startActivity(intent)
        }
    }
}

Explicit intents are used within your own app — you know the exact class you want to launch.

Implicit Intents

Implicit intents declare what action to perform, and the system finds the appropriate component:

// Open a URL in browser
val intent = Intent(Intent.ACTION_VIEW, Uri.parse("https://developer.android.com"))
startActivity(intent)

// Share text
val shareIntent = Intent(Intent.ACTION_SEND).apply {
    type = "text/plain"
    putExtra(Intent.EXTRA_TEXT, "Check out this article!")
}
startActivity(Intent.createChooser(shareIntent, "Share via"))

// Send an email
val emailIntent = Intent(Intent.ACTION_SENDTO).apply {
    data = Uri.parse("mailto:")
    putExtra(Intent.EXTRA_EMAIL, arrayOf("user@example.com"))
    putExtra(Intent.EXTRA_SUBJECT, "Hello")
    putExtra(Intent.EXTRA_TEXT, "Body text")
}
startActivity(emailIntent)

The system resolves implicit intents by matching against intent filters declared in manifests. If multiple apps can handle it, the user sees a chooser dialog.

Intent Filters

Components declare what intents they can handle:

<activity
    android:name=".ui.DeepLinkActivity"
    android:exported="true">
    <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="https"
            android:host="myapp.com"
            android:pathPrefix="/items" />
    </intent-filter>
</activity>

This activity handles URLs like https://myapp.com/items/123.

Passing Data with Extras

Intents carry data via Bundle extras:

// Sending
class ListActivity : AppCompatActivity() {
    private val openDetail = registerForActivityResult(
        ActivityResultContracts.StartActivityForResult()
    ) { result ->
        if (result.resultCode == RESULT_OK) {
            val updated = result.data?.getBooleanExtra("updated", false) ?: false
            if (updated) refreshList()
        }
    }

    fun onItemClick(itemId: String) {
        val intent = Intent(this, DetailActivity::class.java).apply {
            putExtra("itemId", itemId)
            putExtra("isEditing", true)
            putExtra("score", 95.5)
            putStringArrayListExtra("tags", arrayListOf("android", "kotlin"))
        }
        openDetail.launch(intent)
    }
}

// Receiving
class DetailActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        val itemId = intent.getStringExtra("itemId") ?: return
        val isEditing = intent.getBooleanExtra("isEditing", false)
        val score = intent.getDoubleExtra("score", 0.0)
        val tags = intent.getStringArrayListExtra("tags")
    }
}

Serializable vs Parcelable

For complex objects, implement Parcelable (preferred) or Serializable:

@Parcelize
data class Item(
    val id: String,
    val title: String,
    val price: Double
) : Parcelable

// Passing
class ListActivity : AppCompatActivity() {
    private val openDetail = registerForActivityResult(
        ActivityResultContracts.StartActivityForResult()
    ) { /* handle result */ }

    fun openItem(item: Item) {
        val intent = Intent(this, DetailActivity::class.java).apply {
            putExtra("item", item)
        }
        openDetail.launch(intent)
    }
}

// Receiving
class DetailActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        val item = intent.getParcelableExtra<Item>("item") ?: return
    }
}

Parcelable is significantly faster than Serializable on Android because it avoids reflection.

Activity Result API

The modern way to get results from activities:

class ProfileActivity : AppCompatActivity() {
    private val pickImage = registerForActivityResult(
        ActivityResultContracts.GetContent()
    ) { uri: Uri? ->
        uri?.let { displayImage(it) }
    }

    private val requestPermission = registerForActivityResult(
        ActivityResultContracts.RequestPermission()
    ) { granted: Boolean ->
        if (granted) startCamera()
        else showPermissionDenied()
    }

    fun onSelectImage() {
        pickImage.launch("image/*")
    }

    fun onTakePhoto() {
        requestPermission.launch(Manifest.permission.CAMERA)
    }
}

This replaces the deprecated startActivityForResult and onActivityResult pattern.