IOS learning: Debugging programs (breakpoint: exception breakpoint)

I. Exception breakpoint description
When an exception is thrown due to a code problem, the exception breakpoint stops program execution, such as Foundation. some methods in framework, such as NSArray and NSDictionary, will throw an exception if they cannot meet specific conditions. g: array out of bounds. Generally, if no exception breakpoint is set, when the application crashes, it may only display the exception that caused the crash. Even if you read the log, you do not know what happened. After an exception breakpoint is set, the debugger will pause the program execution and locate the line of code with the exception.

An empty project is described as follows:

Create an empty application in xcode and add a line of Exception Code in AppDelegate. m, as shown below:

[Cpp]
(BOOL) application :( UIApplication *) application didfinishlaunchingwitexceptions :( NSDictionary *) launchOptions
{
Self. window = [[UIWindow alloc] initWithFrame: [UIScreen mainScreen] bounds];
// Override point for customization after application launch.
Self. window. backgroundColor = [UIColor whiteColor];

// Adding an exception statement will throw an array out-of-bounds exception.
NSLog (@ "% @", [@ [] objectAtIndex: 10]);

[Self. window makeKeyAndVisible];
Return YES;
}

-(BOOL) application :( UIApplication *) application didfinishlaunchingwitexceptions :( NSDictionary *) launchOptions
{
Self. window = [[UIWindow alloc] initWithFrame: [UIScreen mainScreen] bounds];
// Override point for customization after application launch.
Self. window. backgroundColor = [UIColor whiteColor];

// Adding an exception statement will throw an array out-of-bounds exception.
NSLog (@ "% @", [@ [] objectAtIndex: 10]);

[Self. window makeKeyAndVisible];
Return YES;
}

When an exception breakpoint is not added, the running result is as follows. After the exception is thrown to the main () method:

 

 

Ii. Add an exception breakpoint
Open the breakpoint navigation panel and set an exception breakpoint. Open the Breakpoint navigation panel, click "+" in the lower left corner, select Add Exception Breakpoint, accept the default settings, and Add an Exception Breakpoint, for example:

 

 
 

 

Run the program again and find that the program stops at the line of code that throws an exception, as shown below:

 

 

 

Conclusion: exception breakpoints can help us understand the cause of exceptions. Therefore, when creating a new project, we should first add an exception breakpoint...