Debugging memory leaks with Instruments in Swift - Mini Project: Build & Apply

Debugging memory leaks with Instruments

📖 Scenario: You are building a simple Swift app that manages a list of tasks. Sometimes, the app slows down and uses too much memory. This can happen if objects are not released properly, causing memory leaks.To fix this, you will create a small program with a memory leak, then learn how to identify and fix it using Instruments.

🎯 Goal: Create a Swift class with a memory leak, then fix the leak by using weak references. You will learn how to spot the leak and correct it step-by-step.

📋 What You'll Learn

Create a Swift class called TaskManager with a property tasks that stores an array of strings.

Add a closure property onTaskAdded that captures self strongly, causing a memory leak.

Add a configuration variable taskName to add a new task.

Fix the memory leak by changing the closure to capture self weakly.

Print the tasks list to verify the fix.

💡 Why This Matters

🌍 Real World

Memory leaks can cause apps to slow down or crash. Learning to detect and fix them is important for building smooth, reliable apps.

💼 Career

Understanding memory management and debugging with Instruments is a key skill for iOS developers and software engineers working with Swift.

1

Create the TaskManager class with a memory leak

Create a Swift class called TaskManager with a property tasks initialized as an empty array of strings. Add a closure property called onTaskAdded of type () -> Void? that captures self strongly inside it, causing a memory leak. Initialize onTaskAdded to a closure that appends the string "New Task" to tasks.

Swift

class TaskManager {
    var tasks: [String] = []
    var onTaskAdded: (() -> Void)?
    
    // Your code here
}

Need a hint?

Remember, closures capture variables strongly by default. Here, self is captured inside the closure assigned to onTaskAdded.

2

Add a taskName variable to configure the new task

Add a variable called taskName of type String to the TaskManager class. Initialize it with the value "Important Task".

Swift

class TaskManager {
    var tasks: [String] = []
    var onTaskAdded: (() -> Void)?
    var taskName: String = ""
    
    init() {
        onTaskAdded = {
            self.tasks.append("New Task")
        }
    }
    
    // Your code here
}

Need a hint?

This variable will be used later to add a specific task name.

3

Fix the memory leak by capturing self weakly

Modify the closure assigned to onTaskAdded inside the init() method to capture self weakly. Use [weak self] in the closure capture list. Inside the closure, safely unwrap self and append taskName to tasks.

Swift

class TaskManager {
    var tasks: [String] = []
    var onTaskAdded: (() -> Void)?
    var taskName: String = "Important Task"
    
    init() {
        onTaskAdded = { [weak self] in
            // Your code here
        }
    }
}

Need a hint?

Use [weak self] to avoid strong reference cycles and unwrap self safely inside the closure.

4

Call the closure and print the tasks to verify the fix

Create an instance of TaskManager called manager. Call the onTaskAdded closure on manager. Then, print the tasks property of manager.

Swift

class TaskManager {
    var tasks: [String] = []
    var onTaskAdded: (() -> Void)?
    var taskName: String = "Important Task"
    
    init() {
        onTaskAdded = { [weak self] in
            guard let self = self else { return }
            self.tasks.append(self.taskName)
        }
    }
}

// Your code here

Need a hint?

Calling onTaskAdded should add the task name to the tasks list. Printing tasks shows the updated list.