基本介绍

Objective-C的异常比较像Java的异常处理，也有@finally的处理，不管异常是否捕获都都要执行。
异常处理捕获的语法：

@try {  
      <#statements#>  
  }  
  @catch (NSException *exception) {  
      <#handler#>  
  }  
  @finally {  
      <#statements#>  
  } 

@catch{} 块 对异常的捕获应该先细后粗，即是说先捕获特定的异常，再使用一些泛些的异常类型。

自定义异常

新建SomethingException，SomeOverException这两个类，都继承自NSException类。

SomeException.h

#import <Foundation/Foundation.h>

@interface SomeException : NSException

@end

SomeException.m

#import "SomeException.h"

@implementation SomeException

@end

SomeOverException.h

#import <Foundation/Foundation.h>

@interface SomeOverException : NSException

@end

SomeOverException.m

#import "SomeOverException.h"

@implementation SomeOverException

@end

使用异常

创建Box，在某些条件下产生异常

Box.h

#import <Foundation/Foundation.h>

@interface Box : NSObject {
    NSInteger number;
    
}

-(void) setNum : (NSInteger) num;
-(void) pushIn;
-(void) pushOut;
-(void) print;
@end

Box.m

#import "Box.h"
#import "SomeException.h"
#import "SomeOverException.h"

@implementation Box

-(id) init {
    self = [super init];
    
    if (self) {
        [self setNum:0];
    }
    
    return self;
}


-(void) setNum : (NSInteger) num {
    
    number = num;
    
    if (number > 10) {
        
        //抛出异常
        NSException *exception = [SomeOverException
                                  exceptionWithName:@"BoxWarningException"
                                  reason:@"大于10"
                                  userInfo:nil];
        @throw exception;
        
    } else if (number >= 6) {
        
        NSException *exception = [SomeException
                                  exceptionWithName:@"BoxWarningException"
                                  reason:@"大于6小于10"
                                  userInfo:nil];
        @throw exception;
        
    } else if (number < 0) {
        
        NSException *exception = [SomeOverException
                                  exceptionWithName:@"BoxUnderflowException"
                                  reason:@"小于0"
                                  userInfo:nil];
        @throw exception;
        
    }
    
}

-(void) pushIn {
    
    [self setNum:number + 1];
    
}

-(void) pushOut {
    [self setNum:number -1];
}

-(void) print {
    
    NSLog(@"Box number is %ld.",number);
    
}

@end

捕获异常

#import <Foundation/Foundation.h>
#import "Box.h"
#import "SomeException.h"
#import "SomeOverException.h"

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        // insert code here...
        Box *box = [[Box alloc] init];
        for (int i = 0; i < 6; i++) {
            
            //捕获异常
            @try {
                [box pushIn];
                
            } @catch (SomeException *exception){
                NSLog(@"%@,%@",[exception name],[exception reason]);
            } @catch (SomeOverException *exception){
                NSLog(@"%@",[exception name]);
            }@catch (NSException *exception) {
                
            } @finally {
                [box print];
            }
        }
    }
    return 0;
}

结果打印:

2016-10-10 10:03:05.955611 ExceptionDemo[16423:1308991] Box number is 1.
2016-10-10 10:03:05.955772 ExceptionDemo[16423:1308991] Box number is 2.
2016-10-10 10:03:05.955783 ExceptionDemo[16423:1308991] Box number is 3.
2016-10-10 10:03:05.955791 ExceptionDemo[16423:1308991] Box number is 4.
2016-10-10 10:03:05.955800 ExceptionDemo[16423:1308991] Box number is 5.
2016-10-10 10:03:05.956487 ExceptionDemo[16423:1308991] BoxWarningException,大于6小于10
2016-10-10 10:03:05.956509 ExceptionDemo[16423:1308991] Box number is 6.
Program ended with exit code: 0