GET and POST requests in Android Kotlin - UI Render Trace

Component - GET and POST requests

This UI component shows how an Android app sends GET and POST requests to a web server. It has two buttons: one to fetch data (GET) and one to send data (POST). The results appear below the buttons.

Widget Tree

LinearLayout (vertical)
├─ Button (GET Request)
├─ Button (POST Request)
└─ TextView (Response Display)

A vertical layout with two buttons stacked on top and a text area below to show server responses.

Render Trace - 4 Steps

Step 1: LinearLayout

Step 2: Button (GET Request)

Step 3: Button (POST Request)

Step 4: TextView (Response Display)

State Change - Re-render

Trigger:User taps 'GET Request' or 'POST Request' button

Before

TextView is empty or shows previous response

→

After

TextView updates with new server response text

Re-renders:TextView only re-renders to show updated response

UI Quiz - 3 Questions

What happens when the user taps the 'GET Request' button?

A The app sends a POST request and clears the screen

B The app sends a GET request and shows the response below

C The app closes immediately

D Nothing happens

Key Insight

In mobile apps, network requests like GET and POST are triggered by user actions such as button taps. The UI updates only the parts that show new data, keeping the app responsive and clear. Using a vertical layout with buttons and a text area is a simple way to let users interact and see results immediately.

Practice

1. What is the main purpose of a GET request in Android Kotlin networking?

easy

A. To fetch data from a server

B. To send data to a server

C. To update the UI thread

D. To store data locally

Solution

1. Step 1: Understand GET request purpose

   A GET request is used to retrieve or fetch data from a server without changing any data on the server.

2. Step 2: Compare with other request types

   POST requests send data to the server, unlike GET which only fetches data.

3. Final Answer:

   To fetch data from a server -> Option A

4. Quick Check:

   GET = fetch data [OK]

Hint: GET fetches data; POST sends data [OK]

Common Mistakes:

• Confusing GET with POST request purpose
• Thinking GET modifies server data
• Mixing UI updates with network requests

2. Which of the following is the correct way to start a POST request using Kotlin's HttpURLConnection?

easy

A. connection.requestMethod = "GET"

B. connection.requestMethod = "POST"

C. connection.method = "POST"

D. connection.setRequestMethod("GET")

Solution

1. Step 1: Identify correct property for request method

   In Kotlin, HttpURLConnection uses requestMethod property to set the HTTP method.

2. Step 2: Confirm correct method value for POST

   To make a POST request, set requestMethod to "POST" exactly.

3. Final Answer:

   connection.requestMethod = "POST" -> Option B

4. Quick Check:

   POST method set by requestMethod = "POST" [OK]

Hint: Use requestMethod property with "POST" string [OK]

Common Mistakes:

• Using wrong property name like method
• Setting GET instead of POST
• Using Java-style setRequestMethod() in Kotlin

3. What will be the output of this Kotlin code snippet when making a GET request?

val url = URL("https://example.com/data")
val connection = url.openConnection() as HttpURLConnection
connection.requestMethod = "GET"
val responseCode = connection.responseCode
println(responseCode)

medium

A. 500

B. 404

C. 200

D. Compilation error

Solution

1. Step 1: Understand the code flow

   The code opens a connection to the URL and sets the method to GET, then reads the response code from the server.

2. Step 2: Predict typical HTTP response code

   Assuming the URL is valid and reachable, a successful GET request returns HTTP status code 200.

3. Final Answer:

   200 -> Option C

4. Quick Check:

   Successful GET returns 200 [OK]

Hint: 200 means OK response from server [OK]

Common Mistakes:

• Assuming responseCode is a string
• Confusing 404 (not found) with success
• Thinking code will not compile

4. Identify the error in this Kotlin code snippet for sending a POST request:

val url = URL("https://example.com/api")
val connection = url.openConnection() as HttpURLConnection
connection.requestMethod = "POST"
val outputStream = connection.outputStream
outputStream.write("data=hello".toByteArray())
outputStream.flush()
outputStream.close()

medium

A. Missing setting connection.doOutput = true

B. Using write() instead of writeBytes()

C. Incorrect requestMethod value

D. Not reading the response code

Solution

1. Step 1: Check POST request setup

   For POST requests, doOutput must be set to true to send data in the request body.

2. Step 2: Identify missing property

   The code does not set connection.doOutput = true, so writing to outputStream will fail or not send data.

3. Final Answer:

   Missing setting connection.doOutput = true -> Option A

4. Quick Check:

   doOutput = true needed for POST body [OK]

Hint: Set doOutput true before writing POST data [OK]

Common Mistakes:

• Forgetting doOutput = true for POST
• Confusing write() method usage
• Ignoring response reading after POST

5. You want to send JSON data in a POST request using Kotlin. Which sequence correctly sets up the connection and sends the JSON string {"name":"John"}?

hard

A. Set requestMethod to "GET", write JSON bytes to outputStream, set doOutput = true

B. Set requestMethod to "POST", set doOutput = false, write JSON string directly to connection

C. Set requestMethod to "POST", write JSON bytes to outputStream without setting doOutput, set Content-Type header to "text/plain"

D. Set requestMethod to "POST", set doOutput = true, set Content-Type header to "application/json", write JSON bytes to outputStream

Solution

1. Step 1: Correct HTTP method and output setup

   For sending data, requestMethod must be "POST" and doOutput must be true to allow writing data.

2. Step 2: Set proper headers and write data

   Content-Type header should be "application/json" to indicate JSON data. Then write JSON bytes to outputStream.

3. Final Answer:

   Set requestMethod to "POST", set doOutput = true, set Content-Type header to "application/json", write JSON bytes to outputStream -> Option D

4. Quick Check:

   POST + doOutput + JSON header + write bytes [OK]

Hint: POST JSON needs doOutput true and JSON content-type [OK]

Common Mistakes:

• Using GET method to send data
• Not setting Content-Type header correctly
• Forgetting doOutput = true