SwiftUI Debugging Diagnostics

Advanced diagnostic workflows for SwiftUI issues that persist after basic troubleshooting. Uses Self._printChanges() and SwiftUI Instrument for evidence-based diagnosis.

Symptoms This Diagnoses

Use when you're experiencing:

• View not updating after basic troubleshooting
• Self._printChanges() shows unexpected update patterns
• Intermittent issues ("works sometimes")
• Complex dependency chains causing cascading updates
• Views updating too often (performance)
• Preview crashes that aren't immediately obvious
• State resets unexpectedly

Example Prompts

• "My view isn't updating even though state changed"
• "Self._printChanges() shows @self changed but I don't know why"
• "View updates intermittently — works sometimes, fails others"
• "Too many views updating when I change one value"
• "Preview crashes without clear error message"
• "State resets when navigating back"

Diagnostic Workflow

Claude guides you through evidence-based diagnosis:

Pattern D1: Self._printChanges() Analysis

var body: some View {
    let _ = Self._printChanges()  // Add temporarily
    // Output tells you exactly what triggered update
}

Output interpretation:

• @self changed → View value or environment changed
• propertyName changed → That specific state triggered update
• Nothing logged → Body not being called at all

Pattern D2: SwiftUI Instrument

For complex cases, use Instruments 26:

1. Launch Instruments with SwiftUI template (Cmd-I)
2. Record while reproducing issue
3. Check "Long View Body Updates" lane for expensive views
4. Use "Cause & Effect Graph" to trace data flow

Pattern D3: View Identity Investigation

For state that resets unexpectedly:

• Check for views inside if/else conditionals
• Search for .id() modifiers with changing values
• Verify ForEach uses unique, stable identifiers

Pattern D4: Environment Dependency Check

For cascading updates:

• Search for .environment() modifiers
• Check if frequently-changing values are in environment
• Consider using direct parameters instead

Quick Diagnostic Table

Symptom	First Check	Pattern	Fix Time
View doesn't update	Self._printChanges()	D1	10 min
View updates too often	Instruments	D2	30 min
State resets	.id() modifiers	D3	15 min
Cascade updates	Environment	D4	20 min
Preview crashes	Diagnostics button	D5	10 min

Documentation Scope

This page documents the axiom-swiftui-debugging-diag diagnostic skill—advanced troubleshooting Claude uses when basic SwiftUI debugging doesn't resolve the issue.

For basic troubleshooting: See swiftui-debugging for common issues.

For performance: See swiftui-performance for optimization.

Related

• swiftui-debugging — Basic view update troubleshooting
• swiftui-performance — Performance optimization with Instruments
• xcode-debugging — Environment-first Xcode diagnostics

Resources

WWDC: 2025-306 (SwiftUI Instruments), 2023-10160 (Performance), 2021-10022 (View identity)

Docs: /swiftui, /xcode/instruments