1. Lazy Loading and Deferring Initialization

One of the most effective techniques to speed up app launch time is to defer or “lazy load” non-essential resources and initialization tasks until after the initial screen is loaded. This minimizes the amount of work that needs to be done during startup.

• Avoid heavy computation in application(_:didFinishLaunchingWithOptions:) and other early initialization methods.
• Load resources and assets on-demand instead of pre-loading everything at the start.
• Use lazy initialization for objects that aren’t required during launch but can be initialized as needed in the background.

By reducing the number of tasks your app performs during the launch sequence, you can significantly speed up the cold launch time.

2. Optimize App’s Info.plist

The app’s Info.plist file contains critical metadata that iOS reads when your app launches. Certain keys can impact launch time performance:

• Minimize the size of Info.plist by avoiding unnecessary keys or duplications. Each key-value pair adds to the processing time.
• Ensure that the UIRequiredDeviceCapabilities field is optimized so that iOS knows exactly what features your app requires, helping the system allocate resources efficiently.

3. Reduce the App Binary Size

Large app binaries can increase the time it takes for the system to load your app into memory. You can reduce your app’s binary size by:

• Removing unused resources such as images, fonts, and sounds that aren’t essential during launch.
• Optimizing image assets: Use efficient image formats (like JPEG or WebP over PNG for larger images) and leverage @3x and @2x resources only when necessary.
• Bitcode and App Thinning: Enabling Bitcode and using App Thinning allows the App Store to deliver optimized binaries tailored to each user’s device, reducing the overall size.

4. Profile Launch Time with Xcode Instruments

To make meaningful improvements, it’s important to measure where the time is being spent during launch. Xcode Instruments provides several tools that help you profile app launch performance:

• Time Profiler: Use this to find bottlenecks in your launch sequence. It highlights which methods are taking the most time during startup, allowing you to focus optimization efforts on these areas.
• Activity Monitor: This tool helps track CPU and memory usage, so you can understand which resources are being heavily used during launch.

By regularly profiling your app, you can track the impact of optimizations and ensure that changes are actually improving launch time.

5. Optimize Storyboard and UI Initialization

If you’re using storyboards for your app’s UI, optimizing how these are loaded can have a big impact on launch time:

• Use smaller storyboards: Large or complex storyboards can take longer to load. Break them up into smaller, modular components if possible.
• Avoid unnecessary constraints: Over-complicated Auto Layout constraints can slow down the UI rendering process during launch.
• Optimize views: Ensure that views that aren’t visible immediately aren’t loaded or rendered until necessary. This is especially important for table views and collection views that load large amounts of data.

6. Prewarm Your App with Background Fetch

Using Background Fetch is a way to “prewarm” your app before the user launches it. Background Fetch allows your app to download or process data in the background, so that when the user opens the app, the required data is already available and the app feels faster.

While this doesn’t improve actual launch time, it can improve the perceived performance, which is what ultimately matters to users.

7. Use Swift Concurrency for Efficient Loading

The new Swift Concurrency model (introduced in Swift 5.5) is a powerful tool for optimizing how your app performs tasks in parallel. By offloading non-essential or I/O-bound tasks to background threads, you can prevent the main thread from being blocked during launch.

• Async/await: This allows you to write asynchronous code that’s more efficient, reducing launch time by ensuring the main thread is focused on UI rendering while background tasks handle other operations.
• Task and TaskGroup: These can help execute multiple tasks concurrently, speeding up the time it takes to load assets, initialize components, or fetch data.

8. Cache Data Effectively

Using caching strategies can significantly reduce the time it takes for your app to retrieve data or assets when the user opens it. If certain data is needed frequently during app launch, caching it locally can reduce network requests and processing time.

• User defaults or local storage: For small bits of data like user preferences or app state, store them in NSUserDefaults or a similar local storage method, so you don’t have to fetch them from a server during launch.
• Disk-based caching: For larger resources like images or files, use disk-based caches to store data that can be loaded quickly without making an external request.

9. Use Parallelization to Speed Up Tasks

By running tasks in parallel, you can reduce the time spent on initialization. For example:

• Load multiple resources at once using Dispatch Queues or Operation Queues.
• Perform initialization tasks concurrently where possible, such as loading data while setting up the UI in a separate thread.

This prevents bottlenecks caused by tasks being executed one after another.