Error handling for network calls in Flutter - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to catch exceptions during a network call.

Flutter

try {
  final response = await http.get(Uri.parse('https://api.example.com/data'));
  print(response.body);
} catch ([1]) {
  print('Error occurred');
}

Drag options to blanks, or click blank then click option'

AException

Bint

CString

Ddouble

Attempts:

3 left

💡 Hint

Common Mistakes

Using data types like int or String instead of Exception.

Not using a catch block to handle errors.

The catch block catches exceptions of type Exception during network calls.

2fill in blank

medium

Complete the code to check if the HTTP response status code indicates success.

Flutter

if (response.statusCode [1] 200) {
  print('Success');
} else {
  print('Failed');
}

Drag options to blanks, or click blank then click option'

A==

B>=

C<=

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using greater than or less than operators instead of equality.

Checking for status codes other than 200 for success.

The status code 200 means the request was successful, so we check if it equals 200.

3fill in blank

hard

Fix the error in the catch block to print the error message.

Flutter

try {
  final response = await http.get(Uri.parse('https://api.example.com/data'));
} catch (e) {
  print([1]);
}

Drag options to blanks, or click blank then click option'

Aerror

Be.toString()

Ce.message

Dexception

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to print undefined variables like 'error' or 'exception'.

Using 'e.message' which may not exist on all exceptions.

Using e.toString() converts the error object to a readable string message.

4fill in blank

hard

Fill both blanks to retry the network call only if the status code is 500.

Flutter

if (response.statusCode [1] 500) {
  await Future.delayed(Duration(seconds: [2]));
  // retry logic here
}

Drag options to blanks, or click blank then click option'

A==

B3

C<

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong comparison operators.

Not adding a delay before retrying.

We check if status code equals 500 and wait 3 seconds before retrying.

5fill in blank

hard

Fill all three blanks to create a map of error messages for different status codes.

Flutter

final errorMessages = {
  400: '[1]',
  401: '[2]',
  404: '[3]'
};

Drag options to blanks, or click blank then click option'

ABad Request

BUnauthorized

CNot Found

DSuccess

Attempts:

3 left

💡 Hint

Common Mistakes

Using success message for error codes.

Mixing up error messages for status codes.

These are standard HTTP error messages for the given status codes.

Practice

1. What is the main purpose of using try-catch blocks in Flutter network calls?

easy

A. To automatically retry the network call

B. To speed up the network request

C. To catch and handle errors that may occur during the network request

D. To format the response data

Solution

1. Step 1: Understand the role of try-catch

   The try-catch block is used to catch exceptions or errors that happen during code execution, such as network failures.

2. Step 2: Apply this to network calls

   Network calls can fail due to no internet or server issues, so try-catch helps handle these errors gracefully.

3. Final Answer:

   To catch and handle errors that may occur during the network request -> Option C

4. Quick Check:

   try-catch handles errors = A [OK]

Hint: Try-catch is for catching errors during network calls [OK]

Common Mistakes:

• Thinking try-catch speeds up requests
• Assuming try-catch retries calls automatically
• Using try-catch to format data

2. Which of the following is the correct syntax to catch exceptions in a Flutter network call?

easy

A. try { await http.get(url); } catch (e) { print(e); }

B. try await http.get(url) catch (e) { print(e); }

C. catch (e) { await http.get(url); }

D. http.get(url).try { } catch (e) { print(e); }

Solution

1. Step 1: Recall correct try-catch syntax in Dart

   The try block wraps the code that might throw an error, followed by catch to handle it.

2. Step 2: Check each option

   try { await http.get(url); } catch (e) { print(e); } correctly uses try { await ... } catch (e) { ... } syntax. Others have syntax errors or misplaced keywords.

3. Final Answer:

   try { await http.get(url); } catch (e) { print(e); } -> Option A

4. Quick Check:

   Correct try-catch syntax = B [OK]

Hint: Try-catch wraps code in braces with catch after [OK]

Common Mistakes:

• Omitting braces {} around try block
• Placing await outside try block
• Misplacing catch block

3. Given this code snippet, what will be printed if the server returns status code 404?

try {
  final response = await http.get(Uri.parse('https://example.com/data'));
  if (response.statusCode == 200) {
    print('Success');
  } else {
    print('Failed with status: ' + response.statusCode.toString());
  }
} catch (e) {
  print('Error: ' + e.toString());
}

medium

A. Success

B. No output

C. Error: Exception message

D. Failed with status: 404

Solution

1. Step 1: Analyze the response status code check

   The code checks if statusCode is 200 to print 'Success', else prints failure with status code.

2. Step 2: Apply given status code 404

   Since 404 is not 200, the else block runs printing 'Failed with status: 404'.

3. Final Answer:

   Failed with status: 404 -> Option D

4. Quick Check:

   Non-200 status prints failure message = D [OK]

Hint: Non-200 status triggers else block message [OK]

Common Mistakes:

• Assuming 404 triggers catch block
• Expecting 'Success' for any status
• Ignoring else block

4. Identify the error in this Flutter network call code:

try {
  final response = await http.get('https://example.com');
  if (response.statusCode == 200) {
    print('Data loaded');
  }
} catch (e) {
  print('Error: ' + e.toString());
}

medium

A. Missing await keyword before http.get

B. http.get requires a Uri object, not a String

C. No catch block to handle errors

D. No print statement inside try block

Solution

1. Step 1: Check http.get parameter type

   In Flutter, http.get expects a Uri object, not a plain String.

2. Step 2: Identify the error in the code

   The code passes a String directly, which causes a type error at runtime.

3. Final Answer:

   http.get requires a Uri object, not a String -> Option B

4. Quick Check:

   http.get needs Uri, not String = A [OK]

Hint: Use Uri.parse() to convert String to Uri [OK]

Common Mistakes:

• Passing URL as String directly to http.get
• Forgetting to use Uri.parse()
• Assuming catch block is missing

5. You want to show a friendly message to users when a network call fails due to no internet. Which approach is best in Flutter?

hard

A. Use try-catch to catch exceptions and show a SnackBar with a friendly message

B. Ignore errors and let the app crash to detect bugs

C. Only check response.statusCode without try-catch

D. Use a timer to retry the call without informing the user

Solution

1. Step 1: Understand user experience on network failure

   Users should see a clear message when network fails, not a crash or silent failure.

2. Step 2: Use try-catch and UI feedback

   try-catch catches exceptions like no internet, and showing a SnackBar informs users kindly.

3. Final Answer:

   Use try-catch to catch exceptions and show a SnackBar with a friendly message -> Option A

4. Quick Check:

   Catch errors + show message = C [OK]

Hint: Catch errors and notify user with SnackBar [OK]

Common Mistakes:

• Ignoring errors causing app crashes
• Not informing users about network issues
• Relying only on statusCode without catching exceptions