http package in Flutter - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the http package in Flutter?

The http package allows Flutter apps to send and receive data over the internet using HTTP requests like GET and POST.

beginner

How do you add the http package to a Flutter project?

Add http: ^0.13.6 (or latest version) under dependencies in pubspec.yaml and run flutter pub get.

beginner

What Flutter code snippet sends a simple GET request using the http package?

import 'package:http/http.dart' as http;

void fetchData() async {
  var response = await http.get(Uri.parse('https://example.com'));
  if (response.statusCode == 200) {
    print(response.body);
  }
}

beginner

What does the Uri.parse() method do in the context of the http package?

It converts a string URL into a Uri object, which is required by the http methods to specify the web address.

intermediate

How can you send data with a POST request using the http package?

Use http.post() with the body parameter containing data as a map or encoded string, for example: await http.post(Uri.parse('https://example.com'), body: {'key': 'value'});

Which method from the http package is used to fetch data from a web server?

A http.post()

B http.get()

C http.put()

D http.delete()

http.get() is used to request data from a server, typically to read or fetch information.

What type of object must you pass to http.get() as the URL parameter?

A Uri

B String

C int

D List

The http package requires a Uri object, which you create using Uri.parse() from a string URL.

How do you check if an HTTP request was successful in Flutter using the http package?

A Check if <code>response.statusCode == 404</code>

B Check if <code>response.body != null</code>

C Check if <code>response.headers</code> is empty

D Check if <code>response.statusCode == 200</code>

A status code of 200 means the request succeeded and the server returned the expected data.

Which import statement is correct to use the http package with an alias?

A import 'package:flutter/http.dart';

B import 'http.dart';

C import 'package:http/http.dart' as http;

D import 'http';

This is the standard way to import the http package and use the alias http for its methods.

What is the main difference between http.get() and http.post()?

A <code>get()</code> retrieves data; <code>post()</code> sends data to the server

B <code>get()</code> sends data; <code>post()</code> retrieves data

C Both do the same thing

D <code>post()</code> deletes data; <code>get()</code> updates data

get() is for fetching data, while post() is for sending data to the server, like submitting a form.

Explain how to perform a GET request using the Flutter http package and handle the response.

Think about the steps from importing the package to printing the data.

Describe how to send data to a server using a POST request with the Flutter http package.

Focus on how you include data in the request.

Practice

1.

What does the http.get() function do in Flutter's http package?

easy

A. It deletes data from a server.

B. It sends data to a server.

C. It fetches data from a given URL.

D. It updates data on a server.

Solution

1. Step 1: Understand the purpose of http.get()

   The http.get() method is used to request data from a specified URL.

2. Step 2: Differentiate from other HTTP methods

   Sending data uses http.post(), deleting uses http.delete(), and updating uses http.put() or http.patch().

3. Final Answer:

   It fetches data from a given URL. -> Option C

4. Quick Check:

   http.get() = fetch data [OK]

Hint: Remember: get = fetch, post = send [OK]

Common Mistakes:

• Confusing get() with post()
• Thinking get() sends data
• Mixing HTTP methods

2.

Which of the following is the correct way to create a URI for http.get() in Flutter?

http.get(???);

easy

A. http.get(Uri.parse('https://example.com'))

B. http.get(Uri.https('example.com'))

C. http.get(Uri('https://example.com'))

D. http.get('https://example.com')

Solution

1. Step 1: Check the required argument type for http.get()

   The http.get() method requires a Uri object, not a plain string.

2. Step 2: Use Uri.parse() to convert string to Uri

   The correct way is to wrap the URL string with Uri.parse() to create a Uri object.

3. Final Answer:

   http.get(Uri.parse('https://example.com')) -> Option A

4. Quick Check:

   Use Uri.parse() for URLs in http.get() [OK]

Hint: Always wrap URL string with Uri.parse() [OK]

Common Mistakes:

• Passing URL as plain string
• Using Uri() constructor incorrectly
• Trying Uri.https() without parameters

3.

What will be printed by this Flutter code snippet?

import 'package:http/http.dart' as http;

void fetchData() async {
  final response = await http.get(Uri.parse('https://jsonplaceholder.typicode.com/posts/1'));
  if (response.statusCode == 200) {
    print('Success');
  } else {
    print('Failed');
  }
}

fetchData();

medium

A. SyntaxError

B. Success

C. Failed

D. No output

Solution

1. Step 1: Analyze the HTTP GET request

   The code requests a valid URL that returns a post with status code 200 on success.

2. Step 2: Check the status code condition

   If the status code is 200, it prints 'Success'; otherwise, 'Failed'. The URL is valid and should return 200.

3. Final Answer:

   Success -> Option B

4. Quick Check:

   Status code 200 means Success [OK]

Hint: Status code 200 means success [OK]

Common Mistakes:

• Assuming any response prints 'Failed'
• Ignoring async/await usage
• Not checking statusCode properly

4.

Identify the error in this Flutter code using the http package:

import 'package:http/http.dart' as http;

void sendData() async {
  final response = await http.post('https://example.com/api/data');
  if (response.statusCode == 201) {
    print('Created');
  }
}

medium

A. No error; code is correct.

B. Incorrect status code check; should be 200.

C. http.post() cannot be awaited.

D. Missing Uri.parse() around the URL string.

Solution

1. Step 1: Check the argument type for http.post()

   The http.post() method requires a Uri object, not a plain string.

2. Step 2: Identify missing Uri.parse()

   The URL string should be wrapped with Uri.parse() to convert it to a Uri object.

3. Final Answer:

   Missing Uri.parse() around the URL string. -> Option D

4. Quick Check:

   http.post() needs Uri.parse() for URL [OK]

Hint: Always use Uri.parse() for URLs in http methods [OK]

Common Mistakes:

• Passing URL as string directly
• Confusing status codes 200 and 201
• Forgetting async/await with http calls

5.

You want to send JSON data using http.post() in Flutter. Which code snippet correctly sends a JSON body and sets the content type header?

import 'package:http/http.dart' as http;
import 'dart:convert';

void sendJson() async {
  final url = Uri.parse('https://example.com/api');
  final response = await http.post(
    url,
    headers: ???,
    body: ???,
  );
}

hard

A. {'Content-Type': 'application/json'}, jsonEncode({'key': 'value'})

B. {'content-type': 'text/plain'}, jsonEncode({'key': 'value'})

C. {'Content-Type': 'application/json'}, {'key': 'value'}

D. {'Content-Type': 'application/json'}, json.decode({'key': 'value'})

Solution

1. Step 1: Set the correct header for JSON

   The header must be {'Content-Type': 'application/json'} to tell the server the body is JSON.

2. Step 2: Encode the body as JSON string

   The body must be a string, so use jsonEncode() to convert the map to a JSON string.

3. Final Answer:

   {'Content-Type': 'application/json'}, jsonEncode({'key': 'value'}) -> Option A

4. Quick Check:

   Headers + jsonEncode() = correct JSON POST [OK]

Hint: Use jsonEncode() and set Content-Type header [OK]

Common Mistakes:

• Passing map directly as body
• Wrong content-type header
• Using json.decode() instead of jsonEncode()