In this section, we will delve into advanced debugging techniques in Xcode. These techniques will help you identify and resolve complex issues in your code more efficiently. By the end of this module, you should be comfortable using advanced debugging tools and strategies to troubleshoot and optimize your applications.

1. LLDB (Low-Level Debugger) Commands
2. Watchpoints
3. View Debugging
4. Memory Debugging
5. Symbolic Breakpoints
6. Debugging Multithreaded Applications

LLDB is a powerful debugger that comes with Xcode. It allows you to inspect and manipulate the state of your application while it is running.

• po (Print Object): Prints the description of an object.

  (lldb) po myObject
  

• p (Print): Prints the value of a variable.

  (lldb) p myVariable
  

• bt (Backtrace): Displays the call stack of the current thread.

  (lldb) bt
  

• thread list: Lists all threads in the application.

  (lldb) thread list
  

While debugging, you can use LLDB to inspect the numbers array and the sum variable:

Watchpoints allow you to monitor changes to a specific variable or memory address. This is useful for tracking down issues related to unexpected changes in variable values.

1. Pause the execution of your application.
2. Use the watchpoint set variable command to set a watchpoint on a variable.

   (lldb) watchpoint set variable myVariable
   

Set a watchpoint on counter:

View debugging helps you inspect and debug the view hierarchy of your application. This is particularly useful for resolving layout issues.

1. Run your application in the simulator or on a device.
2. Pause the execution and select the "Debug View Hierarchy" button in the debug toolbar.
3. Inspect the view hierarchy and properties of each view.

Memory debugging tools help you identify memory leaks and issues related to memory management.

1. Run your application.
2. Pause the execution and select the "Debug Memory Graph" button in the debug toolbar.
3. Inspect the memory graph to identify retain cycles and memory leaks.

Symbolic breakpoints allow you to set breakpoints on specific methods or functions, even if you don't have access to the source code.

1. Open the Breakpoint Navigator.
2. Click the "+" button and select "Symbolic Breakpoint".
3. Enter the symbol name (e.g., -[UIViewController viewDidLoad]).

Debugging multithreaded applications can be challenging due to the complexity of concurrent execution.

• Use Thread Sanitizer: Enable Thread Sanitizer in your scheme to detect data races and other threading issues.
• Inspect Thread States: Use the thread list and thread backtrace commands to inspect the state of each thread.
• Set Breakpoints in Critical Sections: Set breakpoints in critical sections of your code to monitor thread execution.

1. Create a new Xcode project.

2. Add the following code to your view controller:

   class MyClass {
       var closure: (() -> Void)?
   }
   
   class ViewController: UIViewController {
       var myObject: MyClass?
   
       override func viewDidLoad() {
           super.viewDidLoad()
           myObject = MyClass()
           myObject?.closure = { [weak self] in
               print(self?.description ?? "No self")
           }
       }
   }
   

3. Run the application and use the Memory Graph Debugger to identify any memory leaks.

4. Fix the memory leak by modifying the closure to capture self weakly.

In this section, we covered advanced debugging techniques in Xcode, including LLDB commands, watchpoints, view debugging, memory debugging, symbolic breakpoints, and debugging multithreaded applications. These tools and techniques will help you identify and resolve complex issues in your code more efficiently. In the next module, we will explore custom build configurations and how to optimize your build process.