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obj-c編程07:異常處理
好了，到了相對輕鬆的話題，也是所有語言無可避免的話題：異常的處理。
我們知道對於一些常見的語言，“異常”是逃不開避不掉的主題：C中相對原始的signal或依賴係統異常支持（比如windows），C++和C#以及java中完善的內置語法，還有ruby中靈活的動態方式，在這裏我們看到的是和java類似的obj-c的方法：
#import <Foundation/Foundation.h>
int main(int argc,char *argv[])
{
@autoreleasepool{
NSLog(@"hello obj-c!");
int i = 0,j = 100;
@try{
i = j / i;
NSLog(@"Do you see me???");
}
@catch(NSException *e){
NSLog(@"caught %@:%@",[e name],[e reason]);
}
}
return 0;
}
我們還可以用@throw拋出自己的異常：
#import <Foundation/Foundation.h>
@interface MyError:NSException
@end
@implementation MyError
-(NSString*)name{
return @"My ERROR!NEVER!";
}
-(NSString*)reason{
return @"NO REASON!";
}
@end
int main(int argc,char *argv[])
{
@autoreleasepool{
NSLog(@"hello obj-c!");
MyError *mye = [[MyError alloc] init];
int i = 0,j = 100;
@try{
@throw mye;
i = j / i;
NSLog(@"Do you see me???");
}
@catch(NSException *e){
NSLog(@"caught %@:%@",[e name],[e reason]);
}
}
return 0;
}
apple@kissAir: objc_src$./3
2014-06-30 11:05:40.389 3[1280:507] hello obj-c!
2014-06-30 11:05:40.391 3[1280:507] *** Terminating app due to uncaught exception of class 'nil'
libc++abi.dylib: terminating with uncaught exception of type nil
Abort trap: 6
呀！執行咋錯了呢？隻能用NSException類嗎？原因不明啊：
#import <Foundation/Foundation.h>
@interface MyError:NSException
@end
@implementation MyError
-(NSString*)name{
return @"My ERROR!NEVER!";
}
-(NSString*)reason{
return @"NO REASON!";
}
@end
int main(int argc,char *argv[])
{
@autoreleasepool{
NSLog(@"hello obj-c!");
//MyError *mye = [[MyError alloc] init];
int i = 0,j = 100;
@try{
@throw [NSException exceptionWithName: @"MyERROR" \
reason: @"NoREASON!" userInfo: nil]3;
i = j / i;
NSLog(@"Do you see me???");
}
@catch(NSException *e){
NSLog(@"caught %@:%@",[e name],[e reason]);
}
}
return 0;
}
最後介紹一下@finally的語法，@finally類似於java中的finally或者ruby中的ensure語句，表示無論發生啥都必須執行的代碼，常常用在確保資源釋放的場所：
int main(int argc,char *argv[])
{
@autoreleasepool{
NSLog(@"hello obj-c!");
//MyError *mye = [[MyError alloc] init];
int i = 0,j = 100;
@try{
@throw [NSException exceptionWithName: @"MyERROR" \
reason: @"NoREASON!" userInfo: nil];
i = j / i;
NSLog(@"Do you see me???");
}
@catch(NSException *e){
NSLog(@"caught %@:%@",[e name],[e reason]);
}
@finally{
NSLog(@"in finally,you must see me!!!");
}
}
return 0;
}
apple@kissAir: objc_src$clang -fobjc-arc -framework Foundation 3.m -o 3
apple@kissAir: objc_src$./3
2014-06-30 11:09:34.263 3[1304:507] hello obj-c!
2014-06-30 11:09:34.265 3[1304:507] caught MyERROR:NoREASON!
2014-06-30 11:09:34.265 3[1304:507] in finally,you must see me!!!
最後更新：2017-04-03 06:03:10