Fixing Common Sentry Errors in Flutter: NoSuchMethodError, StateError, NetworkError

Introduction

In the previous article "Sentry in Baiping's implementation" we covered selection and deployment; this article focuses on the problems encountered during Sentry integration in a Flutter project (Flutter SDK 1.22.6, Dart SDK 2.10.5). The main issues are:

NoSuchMethodError

Flutter official bug (already fixed)

StateError

NetworkError (DNS)

NoSuchMethodError

Problem description

When checking emptiness of List, String, etc., using xxx.isNotEmpty without a null check caused

NoSuchMethodError: The getter 'isNotEmpty' was called on null

.

Solution

// Problem code
if(timeEndList.isNotEmpty){
    ...
}

// Solution
static bool isNotNullOrEmpty<E>(Iterable<E> iterable) => iterable != null && iterable.isNotEmpty;

if (IterableUtils.isNotNullOrEmpty(timeEndList)) {
    ...
}

Check for null before calling isNotEmpty. Encapsulate the check in a utility method to avoid repetition.

Flutter official bug (already fixed)

Problem description

Using NestedScrollView could trigger NoSuchMethodError because position.minScrollExtent may be null, leading to The method '>' was called on null. The issue has been fixed in the master branch.

Solution

// Problem code
bool get hasScrolledBody {
  for (final _NestedScrollPosition position in _innerPositions) {
    assert(position.minScrollExtent != null && position.pixels != null);
    if (position.pixels > position.minScrollExtent) {
      return true;
    }
  }
  return false;
}

// Fixed code
bool get hasScrolledBody {
  for (final _NestedScrollPosition position in _innerPositions) {
    if (!position.hasContentDimensions || !position.hasPixels) {
      continue;
    } else if (position.pixels > position.minScrollExtent) {
      return true;
    }
  }
  return false;
}

StateError

Problem description

Calling list.firstWhere without handling the case where no element matches throws Bad state: No element.

Solution

// Problem code
Map<String, String> getInitialSkuById(String skuId, List<Map<String, dynamic>> skuList) {
  final Map<String, String> selectedKeyValue = <String, String>{};
  final Map<String, dynamic> selectedSku = skuList.firstWhere((Map<String, dynamic> skuItem) => skuItem['id'] == skuId);
  if (selectedSku['stockNum'] > 0) {
    selectedSku.forEach((String k, dynamic v) {
      if (k.contains('keyStr')) {
        selectedKeyValue[k] = v;
      }
    });
  }
  return selectedKeyValue;
}

// Fixed code
Map<String, String> getInitialSkuById(String skuId, List<Map<String, dynamic>> skuList) {
  final Map<String, String> selectedKeyValue = <String, String>{};
  final Map<String, dynamic>? selectedSku = skuList.firstWhere(
    (Map<String, dynamic> skuItem) => skuItem['id'] == skuId,
    orElse: () => null,
  );
  if (selectedSku != null && selectedSku['stockNum'] > 0) {
    selectedSku.forEach((String k, dynamic v) {
      if (k.contains('keyStr')) {
        selectedKeyValue[k] = v;
      }
    });
  }
  return selectedKeyValue;
}

Use the orElse parameter or firstWhereOrNull to avoid the exception when no element matches.

NetworkError (DNS)

Problem description

DNS resolution failures can cause network requests to fail, leading to errors such as timeouts or unreachable hosts.

Solution

Consider using reliable DNS services like Alibaba Cloud DNS or Tencent Mobile DNS to improve stability.

DNS Basics

What is DNS

Domain hierarchical structure

DNS layered architecture

DNS resolution process

DNS (Domain Name System) is a core Internet service that maps domain names to IP addresses, allowing users to access resources without remembering numeric IPs.

Domain hierarchy

Internet naming uses a tree‑like hierarchy: top‑level domain (e.g., .com), second‑level domain (e.g., baiping.com), sub‑domains (e.g., example.baiping.com), and further sub‑domains.

DNS resolution steps

User enters a domain in the browser; the local resolver starts a recursive query.

The resolver iteratively queries the root server.

The root server returns the address of the TLD server.

The resolver queries the TLD server.

The TLD server returns the authoritative server for the domain.

The resolver queries the authoritative server.

The authoritative server returns the IP address.

The resolver sends the IP to the browser, which then makes the HTTP request.

Conclusion

The four error types—NoSuchMethodError, Flutter framework bug, StateError, and NetworkError—are common during early development. Understanding their causes and applying the provided fixes can help prevent similar issues in future projects.