Objective-c异常处理

o 异常情况（Exceptions）
 注意：异常处理只有 Mac OS X 10.3 以上才支持。
 基于 "Programming in Objective-C," Copyright © 2004 by Sams Publishing一书中的范例，并经过允许而刊载。
CupWarningException.h
#import <Foundation/NSException.h>
@interface CupWarningException: NSException
@end
CupWarningException.m
#import "CupWarningException.h"
@implementation CupWarningException
@end
CupOverflowException.h
#import <Foundation/NSException.h>
@interface CupOverflowException: NSException
@end
CupOverflowException.m
#import "CupOverflowException.h"
@implementation CupOverflowException
@end
Cup.h
#import <Foundation/NSObject.h>
@interface Cup: NSObject {
int level;
}
-(int) level;
-(void) setLevel: (int) l;
-(void) fill;
-(void) empty;
-(void) print;
@end
Cup.m
#import "Cup.h"
#import "CupOverflowException.h"
#import "CupWarningException.h"
#import <Foundation/NSException.h>
#import <Foundation/NSString.h>
@implementation Cup
-(id) init {
self = [super init];
if ( self ) {
[self setLevel: 0];
}
return self;
}
-(int) level {
return level;
}
-(void) setLevel: (int) l {
level = l;
if ( level > 100 ) {
// throw overflow
NSException *e = [CupOverflowException
exceptionWithName: @"CupOverflowException"
reason: @"The level is above 100"
userInfo: nil];
@throw e;
} else if ( level >= 50 ) {
// throw warning
NSException *e = [CupWarningException
exceptionWithName: @"CupWarningException"
reason: @"The level is above or at 50"
userInfo: nil];
@throw e;
} else if ( level < 0 ) {
// throw exception
NSException *e = [NSException
exceptionWithName: @"CupUnderflowException"
reason: @"The level is below 0"
userInfo: nil];
@throw e;
}
}
-(void) fill {
[self setLevel: level + 10];
}
-(void) empty {
[self setLevel: level - 10];
}
-(void) print {
printf( "Cup level is: %i/n", level );
}
@end
main.m
#import "Cup.h"
#import "CupOverflowException.h"
#import "CupWarningException.h"
#import <Foundation/NSString.h>
#import <Foundation/NSException.h>
#import <Foundation/NSAutoreleasePool.h>
#import <stdio.h>
int main( int argc, const char *argv[] ) {
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
Cup *cup = [[Cup alloc] init];
int i;
// this will work
for ( i = 0; i < 4; i++ ) {
[cup fill];
[cup print];
}
// this will throw exceptions
for ( i = 0; i < 7; i++ ) {
@try {
[cup fill];
} @catch ( CupWarningException *e ) {
printf( "%s: ", [[e name] cString] );
} @catch ( CupOverflowException *e ) {
printf( "%s: ", [[e name] cString] );
} @finally {
[cup print];
}
}
// throw a generic exception
@try {
[cup setLevel: -1];
} @catch ( NSException *e ) {
printf( "%s: %s/n", [[e name] cString], [[e reason] cString] );
}
// free memory
[cup release];
[pool release];
}
output
Cup level is: 10
Cup level is: 20
Cup level is: 30
Cup level is: 40
CupWarningException: Cup level is: 50
CupWarningException: Cup level is: 60
CupWarningException: Cup level is: 70
CupWarningException: Cup level is: 80
CupWarningException: Cup level is: 90
CupWarningException: Cup level is: 100
CupOverflowException: Cup level is: 110
CupUnderflowException: The level is below 0
NSAutoreleasePool 是一个内存管理类别。现在先别管它是干嘛的。
Exceptions（异常情况）的丢出不需要扩充（extend）NSException 对象，你可简单的用 id 来代表它： @catch ( id e ) { ... }
还有一个 finally 区块，它的行为就像 Java 的异常处理方式，finally 区块的内容保证会被呼叫。
Cup.m 里的 @"CupOverflowException" 是一个 NSString 常数物件。在 Objective-C 中，@ 符号通常用来代表这是语言的衍生部分。C 语言形式的字符串（C string）就像 C/C++ 一样是 "String constant" 的形式，型别为 char *。