Table of Contents

• Introduction
  • Example: UI Event Interception (Code, Stack Trace)
• Summary

Introduction

The Blue Triangle SDK captures and reports crashes and errors to help correlate user-experience issues with business impact. Because of this, you may see Blue Triangle SDK methods appear in a crash stack trace. This does not necessarily mean the SDK caused the crash—only that it detected the crash and was in the call chain when it reported it.

Example: UI Event Interception

To track user interactions such as taps, the Blue Triangle SDK intercepts UI events before they reach the application own code. This technique is common across analytics and monitoring SDKs.

As a result, if your app crashes during a user interaction—such as a tap—the SDK may appear in the stack trace even when the root cause is entirely within your app.

Consider the following example, where tapping a button triggers an exception:

private lazy var checkoutButton: UIButton = {
   let action = UIAction(title: "Checkout") { [weak self] _ in
       // This will crash because the array is empty
       NSArray().object(at: 99)
   }
   return UIButton(primaryAction: action)
}()

When the user taps this button, the app will crash inside the button’s action. However, because the SDK intercepts the tap to record it, the crash stack trace will show SDK methods above the line where the exception occurred.

Sample Stack Trace

Below is what the resulting crash log looks like in Xcode. Note that the crash originates from RootViewController inside the app code, while Blue Triangle appear higher in the stack simply because it intercepts the user event:

0   CoreFoundation                	       0x1804f39dc __exceptionPreprocess + 160
1   libobjc.A.dylib               	       0x18009c084 objc_exception_throw + 72
2   CoreFoundation                	       0x1803bb2e8 -[__NSArray0 objectEnumerator] + 0
3   Example-UIKit                 	       0x1007a0124 specialized RootViewController.causeNSException() + 64 (RootViewController.swift:177)
4   Example-UIKit                 	       0x10079e8c0 closure #1 in closure #1 in RootViewController.crashButton.getter + 60
5   UIKitCore                     	       0x1851aea08 0x185156000 + 363016
6   UIKitCore                     	       0x1861b0fcc -[UIAction performWithSender:target:] + 104
7   UIKitCore                     	       0x185ae7e6c -[UIControl _sendActionsForEvents:withEvent:] + 284
8   UIKitCore                     	       0x185ae464c -[UIButton _sendActionsForEvents:withEvent:] + 200
9   UIKitCore                     	       0x185ae7ed0 -[UIControl _sendActionsForEvents:withEvent:] + 384
10  UIKitCore                     	       0x185ae464c -[UIButton sendActionsForEvents:withEvent:] + 200
11  UIKitCore                     	       0x185ae6aec -[UIControl touchesEnded:withEvent:] + 428
12  UIKitCore                     	       0x186299fe4 -[UIWindow sendTouchesForEvent:] + 976
13  UIKitCore                     	       0x18629b3e4 -[UIWindow sendEvent:] + 2812
14  UIKitCore                     	       0x186279714 -[UIApplication sendEvent:] + 376
15  Example-UIKit                 	       0x100804148 UIApplication.swizzled_sendEvent(:) + 56 (UIApplication+Utils.swift:62)
16  Example-UIKit                 	       0x100804544 @objc UIApplication.swizzled_sendEvent(:) + 52
17  UIKitCore                     	       0x18630dc6c __dispatchPreprocessedEventFromEventQueue + 1184
18  UIKitCore                     	       0x186310920 __processEventQueue + 4800
19  UIKitCore                     	       0x186308ecc updateCycleEntry + 168
20  UIKitCore                     	       0x185773878 _UIUpdateSequenceRunNext + 120
21  UIKitCore                     	       0x18617ec90 schedulerStepScheduledMainSectionContinue + 56
22  UpdateCycle                   	       0x2509462b4 UC::DriverCore::continueProcessing() + 80
23  CoreFoundation                	       0x1804114ac __CFMachPortPerform + 164
24  CoreFoundation                	       0x18044dbe0 

Though Frames 15 and 16 show the file name and line number (UIApplication+Utils.swift:62), but this is not initiated from BlueTriangle SDK.

Since we intercept sendEvent(:) using swizzled implementation SDK forwards the event back to UIKit’s original sendEvent(:) which is indicated in stack trace frame 13, 14, 15.

13  UIKitCore     0x18629b3e4 -[UIWindow sendEvent:] + 2812
14  UIKitCore     0x186279714 -[UIApplication sendEvent:] + 376
15  Example-UIKit 0x100804148 UIApplication.swizzled_sendEvent(:) + 56 (UIApplication+Utils.swift:62)

Hence presence of “14  UIKitCore      [UIApplication sendEvent:] + 376” indicates that the event successfully passed through our interception layer and was handed back to UIKit, which ultimately leads to the app’s event handlers.

The real crash in this example actually occurs at frames 3 and 4:

2   CoreFoundation 0x1803bb2e8 -[__NSArray0 objectEnumerator] + 0
3   Example-UIKit  0x1007a0124 specialized RootViewController.causeNSException() + 64 (RootViewController.swift:177)

Unlike the above example, in some special cases the first few frames may not indicate app code like frames 3 and 4 in the stack trace. Still, the presence of: 14  UIKitCore      [UIApplication sendEvent:] + 376 indicates that the BlueTriangle interceptor passed execution successfully back to UIKit, and the issue could instead be related to memory handling within the event handlers.

Summary

When investigating an app crash:

• Start by reviewing the crash in the Error Explorer within the portal. There, you can see details such as the device, OS version, application version, and SDK version. If you have session replay enabled, you can also view the user’s actions leading up to the crash. Together, these details can help narrow down the root cause.

• Share the crash information—including app details, the stack trace, and any other relevant context—with Blue Triangle’s customer support team for further assistance.