Deep links in Android Kotlin - Mini App: Build & Ship

Build: DeepLinkDemoScreen

This screen handles deep links to show a message passed in the URL.

Target UI

-------------------------
| Deep Link Demo        |
|-----------------------|
| Message:              |
| [                    ]|
|                       |
| (Open app via deep link)|
-------------------------

Handle deep links with scheme 'myapp' and host 'showmessage'

Extract 'msg' query parameter from the deep link URL

Display the extracted message on the screen

Show a default message if no deep link or no message parameter

Starter Code

Android Kotlin

package com.example.deeplinkdemo

import android.content.Intent
import android.net.Uri
import android.os.Bundle
import android.widget.TextView
import androidx.appcompat.app.AppCompatActivity

class DeepLinkDemoScreen : AppCompatActivity() {
    private lateinit var messageTextView: TextView

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_deep_link_demo_screen)

        messageTextView = findViewById(R.id.messageTextView)

        // TODO: Handle the incoming intent for deep link
    }
}

Task 1

Task 2

Task 3

Task 4

Solution

Android Kotlin

package com.example.deeplinkdemo

import android.content.Intent
import android.net.Uri
import android.os.Bundle
import android.widget.TextView
import androidx.appcompat.app.AppCompatActivity

class DeepLinkDemoScreen : AppCompatActivity() {
    private lateinit var messageTextView: TextView

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_deep_link_demo_screen)

        messageTextView = findViewById(R.id.messageTextView)

        val data: Uri? = intent?.data
        if (data != null && data.scheme == "myapp" && data.host == "showmessage") {
            val message = data.getQueryParameter("msg") ?: "No message found"
            messageTextView.text = message
        } else {
            messageTextView.text = "Welcome! Open this screen via a deep link."
        }
    }
}

We check if the intent has data (a Uri). Then we verify the scheme is 'myapp' and the host is 'showmessage' to confirm it's our deep link. We extract the 'msg' query parameter from the Uri and display it in the TextView. If no deep link or message is found, we show a default welcome message.

Final Result

Completed Screen

-------------------------
| Deep Link Demo        |
|-----------------------|
| Message:              |
| Hello from deep link! |
|                       |
| (Open app via deep link)|
-------------------------

When user opens the app via a deep link like myapp://showmessage?msg=Hello%20from%20deep%20link!, the message text updates to 'Hello from deep link!'

If app is opened normally, the message shows the default welcome text

Stretch Goal

Add support for deep links with a path parameter instead of query parameter, e.g., myapp://showmessage/HelloWorld

💡 Hint

Use Uri.getPathSegments() to extract the message from the path segments

Practice

1. What is the main purpose of a deep link in an Android app?

easy

A. To open a specific screen inside the app from an external URL

B. To update the app's user interface colors

C. To increase the app's memory usage

D. To change the app's icon on the home screen

Solution

1. Step 1: Understand deep link functionality

   Deep links allow an app to open a specific screen or content when a user clicks a URL outside the app.

2. Step 2: Compare options with this purpose

   Only To open a specific screen inside the app from an external URL describes opening a specific screen from an external URL, which matches deep link behavior.

3. Final Answer:

   To open a specific screen inside the app from an external URL -> Option A

4. Quick Check:

   Deep link purpose = open specific screen [OK]

Hint: Deep links open app screens from outside links [OK]

Common Mistakes:

• Confusing deep links with UI styling
• Thinking deep links change app icons
• Assuming deep links increase memory

2. Which XML element is used to declare a deep link in AndroidManifest.xml?

easy

A. <provider>

B.

C. <service>

D. <activity>

Solution

1. Step 1: Identify where deep links are declared

   Deep links are declared inside an element within an activity in AndroidManifest.xml.

2. Step 2: Match options to this element

   Only is used to specify deep link URL patterns and actions.

3. Final Answer:

   <intent-filter> -> Option B

4. Quick Check:

   Deep links declared in intent-filter [OK]

Hint: Deep links go inside intent-filter tags [OK]

Common Mistakes:

• Confusing activity tag with deep link declaration
• Using service or provider tags incorrectly
• Not nesting intent-filter inside activity

3. Given this intent filter snippet in AndroidManifest.xml, what URL will open the app's activity?

<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="example.com" android:pathPrefix="/profile" />
</intent-filter>

medium

A. https://example.com/about

B. http://example.com/profile

C. https://example.com/profile/settings

D. https://example.org/profile

Solution

1. Step 1: Analyze the intent filter data attributes

   The scheme is https, host is example.com, and pathPrefix is /profile, so URLs starting with https://example.com/profile will match.

2. Step 2: Check each option against these rules

   https://example.com/profile/settings matches https scheme, example.com host, and path starting with /profile. Options B (http scheme), C (wrong path), and D (wrong host) do not match.

3. Final Answer:

   https://example.com/profile/settings -> Option C

4. Quick Check:

   Match scheme, host, pathPrefix = https://example.com/profile/settings [OK]

Hint: Match scheme, host, and pathPrefix exactly [OK]

Common Mistakes:

• Ignoring scheme (http vs https)
• Confusing host names
• Not checking pathPrefix carefully

4. What is wrong with this intent filter for a deep link?

<intent-filter>
  <action android:name="android.intent.action.VIEW" />
  <category android:name="android.intent.category.LAUNCHER" />
  <data android:scheme="myapp" />
</intent-filter>

medium

A. It uses LAUNCHER category instead of BROWSABLE

B. It is missing the action VIEW

C. The scheme attribute is invalid

D. It should be inside a service tag

Solution

1. Step 1: Check required categories for deep links

   Deep links require the BROWSABLE category to allow opening from browsers or external apps.

2. Step 2: Identify incorrect category usage

   This intent filter uses LAUNCHER category, which is for app launchers, not deep links.

3. Final Answer:

   It uses LAUNCHER category instead of BROWSABLE -> Option A

4. Quick Check:

   Deep links need BROWSABLE category [OK]

Hint: Deep links need BROWSABLE, not LAUNCHER category [OK]

Common Mistakes:

• Using LAUNCHER category for deep links
• Forgetting to add BROWSABLE category
• Placing intent-filter inside wrong tag

5. You want your app to open a user profile screen when a link like myapp://user/123 is clicked. Which intent filter correctly handles this deep link?

hard

A. \n \n \n \n

B. \n \n \n \n \n

C. \n \n \n \n

D. \n \n \n \n \n

Solution

1. Step 1: Check required action and categories for deep links

   Deep links need action VIEW and categories DEFAULT and BROWSABLE to work properly.

2. Step 2: Verify data attributes match the URL pattern

   The URL myapp://user/123 has scheme="myapp", host="user", path="/123". Needs matching scheme, host, and pathPattern="/.*" for variable IDs.

3. Step 3: Compare options

   The filter with scheme="myapp", host="user", pathPattern="/.*", VIEW action, DEFAULT and BROWSABLE matches perfectly. pathPrefix="/user" without host mismatches path="/123". Missing BROWSABLE limits external opening. MAIN/LAUNCHER is incorrect for deep links.

4. Final Answer:

   Intent filter with VIEW action, DEFAULT/BROWSABLE categories, scheme myapp, host user, pathPattern /.* -> Option D

5. Quick Check:

   scheme=myapp host=user pathPattern=/.* VIEW BROWSABLE [OK]

Hint: VIEW action, DEFAULT/BROWSABLE categories, scheme+host+pathPattern [OK]

Common Mistakes:

• Missing BROWSABLE category
• Using MAIN action instead of VIEW
• Confusing pathPrefix with host+pathPattern
• Wrong categories for deep links