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Fix app_start trace not firing in SwiftUI apps using @UIApplicationDelegateAdaptor (#15802) #15912

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Fix app_start trace not firing in SwiftUI apps using @UIApplicationDelegateAdaptor (#15802) #15912

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92a8fa1
Fix app_start trace skipping in SwiftUI apps (#15802)
JesusRojass Mar 6, 2026
02915e8
Merge branch 'firebase:main' into JesusRojass/#15802
JesusRojass Mar 6, 2026
ae249f3
Scope deferred background check to scene based apps
JesusRojass Mar 6, 2026
4eedd53
Merge branch 'firebase:main' into JesusRojass/#15802
JesusRojass Mar 9, 2026
21f96ce
Update CHANGELOG.md
JesusRojass Mar 9, 2026
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41 changes: 27 additions & 14 deletions FirebasePerformance/Sources/AppActivity/FPRAppActivityTracker.m
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Original file line number Diff line number Diff line change
Expand Up @@ -34,6 +34,7 @@
static FPRCPUGaugeData *gAppStartCPUGaugeData = nil;
static FPRMemoryGaugeData *gAppStartMemoryGaugeData = nil;
static BOOL isActivePrewarm = NO;
static BOOL sLaunchedInBackgroundState = NO;

NSString *const kFPRAppStartTraceName = @"_as";
NSString *const kFPRAppStartStageNameTimeToUI = @"_astui";
Expand Down Expand Up @@ -118,15 +119,18 @@ + (void)windowDidBecomeVisible:(NSNotification *)notification {
+ (void)applicationDidFinishLaunching:(NSNotification *)notification {
applicationDidFinishLaunchTime = [NSDate date];

// Detect a background launch and invalidate app start time
// this prevents we measure duration from background launch
UIApplicationState state = [UIApplication sharedApplication].applicationState;
if (state == UIApplicationStateBackground) {
// App launched in background so we invalidate the captured app start time
// to prevent incorrect measurement when user later opens the app
appStartTime = nil;
FPRLogDebug(kFPRTraceNotCreated,
@"Background launch detected. App start measurement will be skipped.");
NSDictionary *sceneManifest =
[[NSBundle mainBundle] objectForInfoDictionaryKey:@"UIApplicationSceneManifest"];
if (sceneManifest) {
// Scene-based apps may report .background here even on foreground launches
// because scenes haven't connected yet. Defer decision to didBecomeActive.
sLaunchedInBackgroundState = YES;
} else {
// Non-scene app - .background is reliable, invalidate app start.
appStartTime = nil;
}
}

[[NSNotificationCenter defaultCenter] removeObserver:self
Expand Down Expand Up @@ -259,15 +263,25 @@ - (void)appDidBecomeActiveNotification:(NSNotification *)notification {

static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
// Early bailout if background launch was detected, appStartTime will be nil if the app was
// launched in background
if (appStartTime == nil) {
FPRLogDebug(kFPRTraceNotCreated,
@"App start trace skipped due to background launch. "
@"This prevents reporting incorrect multi-minute/hour durations.");
FPRLogDebug(kFPRTraceNotCreated, @"App start trace skipped due to background launch.");
return;
}

// Distinguish genuine background launches by checking how long ago +load captured appStartTime.
// A real foreground launch reaches didBecomeActive within seconds; a background launch that is
// later opened by the user will have a much larger gap.
if (sLaunchedInBackgroundState) {
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@visumickey visumickey Mar 6, 2026

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Worried about a scenario where a non-switftUI app starts itself in background, but the app gets launched before the max app start duration value - this code would account for that app start time.

I think the ideal would be differentiate if this is a SwiftUI app and make some exceptions rather than impacting all the scenarios.

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@JesusRojass JesusRojass Mar 6, 2026

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I have added a commit that checks for UIApplicationSceneManifest in the info.plist before deferring to keep the original behavior in the rest of the escenarios

LMK what you think 😄

NSTimeInterval timeSinceStart = [[NSDate date] timeIntervalSinceDate:appStartTime];
// App launched in background so we invalidate the captured app start time
// to prevent incorrect measurement when user later opens the app
Comment on lines +276 to +277
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@gemini-code-assist gemini-code-assist bot Mar 6, 2026

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low

This comment is a bit misleading as it appears to be a leftover from the previous implementation. The code no longer invalidates appStartTime. It just skips the app start trace if it's determined to be a genuine background launch. Consider updating the comment to more accurately reflect the current logic.

Suggested change
// App launched in background so we invalidate the captured app start time
// to prevent incorrect measurement when user later opens the app
// If the time since launch is too long, it's a genuine background launch.

if (timeSinceStart > gAppStartMaxValidDuration) {
FPRLogDebug(kFPRTraceNotCreated,
@"Background launch detected. App start measurement will be skipped.");
return;
}
}

self.appStartTrace = [[FIRTrace alloc] initInternalTraceWithName:kFPRAppStartTraceName];
[self.appStartTrace startWithStartTime:appStartTime];
[self.appStartTrace startStageNamed:kFPRAppStartStageNameTimeToUI startTime:appStartTime];
Expand All @@ -281,8 +295,7 @@ - (void)appDidBecomeActiveNotification:(NSNotification *)notification {
self.appStartTrace.backgroundTraceState != FPRTraceStateForegroundOnly) {
[self.appStartTrace cancel];
self.appStartTrace = nil;
FPRLogDebug(kFPRTraceNotCreated,
@"App start trace cancelled due to background state contamination.");
FPRLogDebug(kFPRTraceNotCreated, @"App start trace cancelled. Trace had background state.");
}

// Stop the active background session trace.
Expand Down
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