@try - catch block in Objective-C

问题

Why doesn't @try block work? It crashed the app, but it was supposed to be caught by the @try block.

 NSString* test = [NSString stringWithString:@"ss"];

 @try {
    [test characterAtIndex:6];

 }
 @catch (NSException * e) {
    NSLog(@"Exception: %@", e);
 }
 @finally {
    NSLog(@"finally");
 }

回答1:

All work perfectly :)

 NSString *test = @"test";
 unichar a;
 int index = 5;

 @try {
    a = [test characterAtIndex:index];
 }
 @catch (NSException *exception) {
    NSLog(@"%@", exception.reason);
    NSLog(@"Char at index %d cannot be found", index);
    NSLog(@"Max index is: %lu", [test length] - 1);
 }
 @finally {
    NSLog(@"Finally condition");
 }

Log:

[__NSCFConstantString characterAtIndex:]: Range or index out of bounds

Char at index 5 cannot be found

Max index is: 3

Finally condition

回答2:

Now I've found the problem.

Removing the obj_exception_throw from my breakpoints solved this. Now it's caught by the @try block and also, NSSetUncaughtExceptionHandler will handle this if a @try block is missing.

回答3:

Objective-C is not Java. In Objective-C exceptions are what they are called. Exceptions! Don’t use them for error handling. It’s not their proposal. Just check the length of the string before using characterAtIndex and everything is fine....

来源：https://stackoverflow.com/questions/3363612/try-catch-block-in-objective-c