Objective-C语法之异常处理

Bertha 。 2022-08-07 05:55 123阅读 0赞

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：

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1.  @**try** \{ 
2.   <\#statements\#> 
3.   \} 
4.   @**catch** (NSException \*exception) \{ 
5.   <\#handler\#> 
6.   \} 
7.   @finally \{ 
8.   <\#statements\#> 
9.   \}

@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。

我们自定义两个异常类，看看异常异常处理的使用。

## 1、新建SomethingException，SomeOverException这两个类，都继承与NSException类。 ##

SomethingException.h

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1.  \#import <Foundation/Foundation.h>
2.  
3.  @interface SomethingException : NSException 
4.  
5.  @end

SomethingException.m

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1.  \#import "SomethingException.h"
2.  
3.  @implementation SomethingException 
4.  
5.  @end

SomeOverException.h

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1.  \#import <Foundation/Foundation.h>
2.  
3.  @interface SomeOverException : NSException 
4.  
5.  @end

SomeOverException.m

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1.  \#import "SomeOverException.h"
2.  
3.  @implementation SomeOverException 
4.  
5.  @end

## 2、新建Box类，在某些条件下产生异常。 ##

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1.  \#import <Foundation/Foundation.h>
2.  
3.  @interface Box : NSObject 
4.  \{ 
5.   NSInteger number; 
6.  \} 
7.  \-(**void**) setNumber: (NSInteger) num; 
8.  \-(**void**) pushIn; 
9.  \-(**void**) pullOut; 
10. \-(**void**) printNumber; 
11. @end

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1.  @implementation Box 
2.  \-(id) init \{ 
3.   self = \[super init\]; 
4.  
5.  **if** ( self ) \{ 
6.   \[self setNumber: 0\]; 
7.   \} 
8.  
9.  **return** self; 
10. \} 
11. 
12. \-(**void**) setNumber: (NSInteger) num \{ 
13.  number = num; 
14. 
15. **if** ( number > 10 ) \{ 
16.  NSException \*e = \[SomeOverException 
17.  exceptionWithName: @"BoxOverflowException"
18.  reason: @"The level is above 100"
19.  userInfo: nil\]; 
20.  @**throw** e; 
21.  \} **else****if** ( number >= 6 ) \{ 
22. // throw warning
23.  NSException \*e = \[SomethingException 
24.  exceptionWithName: @"BoxWarningException"
25.  reason: @"The level is above or at 60"
26.  userInfo: nil\]; 
27.  @**throw** e; 
28.  \} **else****if** ( number < 0 ) \{ 
29. // throw exception
30.  NSException \*e = \[NSException 
31.  exceptionWithName: @"BoxUnderflowException"
32.  reason: @"The level is below 0"
33.  userInfo: nil\]; 
34.  @**throw** e; 
35.  \} 
36. \} 
37. 
38. \-(**void**) pushIn \{ 
39.  \[self setNumber: number + 1\]; 
40. \} 
41. 
42. \-(**void**) pullOut \{ 
43.  \[self setNumber: number - 1\]; 
44. \} 
45. 
46. \-(**void**) printNumber \{ 
47.  NSLog(@"Box number is: %d", number); 
48. \} 
49. @end

这个类的作用是，初始化Box时，number数字是0，可以用pushIn 方法往Box里推入数字，每调用一次，number加1.当number数字大于等于6时产生SomethingException异常,告诉你数字达到或超过6了，超过10时产生SomeOverException异常，小于1时产生普通的NSException异常。

这里写 \[SomeOverException exceptionWithName:@"BoxOverflowException" reason:@"The level is above 100"异常的名称和理由，在捕获时可以获取。

## 3、使用Box，在适当添加下捕获Box类的异常 ##

### 3.1、在没超过6时，没有异常 ###

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1.  \- (**void**)viewDidLoad 
2.  \{ 
3.   \[super viewDidLoad\]; 
4.   NSAutoreleasePool \*pool = \[\[NSAutoreleasePool alloc\] init\]; 
5.   Box \*box = \[\[Box alloc\]init\]; 
6.  **for** (**int** i = 0; i < 5; i++) \{ 
7.   \[box pushIn\]; 
8.   \[box printNumber\]; 
9.   \} 
10. \}

打印结果：

**Box number is: 1**

**Box number is: 2**

**Box number is: 3**

**Box number is: 4**

**Box number is: 5**

### 3.2 超过6，产生异常 ###

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1.  **for** (**int** i = 0; i < 11; i++) \{ 
2.   \[box pushIn\]; 
3.   \[box printNumber\]; 
4.   \}

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1.  2012-07-04 09:12:05.889 ObjectiveCTest\[648:f803\] Box number is: 1 
2.  2012-07-04 09:12:05.890 ObjectiveCTest\[648:f803\] Box number is: 2 
3.  2012-07-04 09:12:05.890 ObjectiveCTest\[648:f803\] Box number is: 3 
4.  2012-07-04 09:12:05.890 ObjectiveCTest\[648:f803\] Box number is: 4 
5.  2012-07-04 09:12:05.891 ObjectiveCTest\[648:f803\] Box number is: 5 
6.  2012-07-04 09:12:05.891 ObjectiveCTest\[648:f803\] \*\*\* Terminating app due to uncaught exception 'BoxWarningException', reason: 'The number is above or at 60'

这是时，程序抛出异常崩溃了。那怎么使程序不崩溃呢，做异常处理。

### 3.3、加上异常处理 ###

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1.  **for** (**int** i = 0; i < 11; i++) \{ 
2.   @**try** \{ 
3.   \[box pushIn\]; 
4.   \} 
5.   @**catch** (SomethingException \*exception) \{ 
6.   NSLog(@"%@ %@", \[exception name\], \[exception reason\]); 
7.   \} 
8.   @**catch** (SomeOverException \*exception) \{ 
9.   NSLog(@"%@", \[exception name\]); 
10.  \} 
11.  @finally \{ 
12.  \[box printNumber\]; 
13.  \} 
14.  \}

运行，程序没有崩溃，打印结果：

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1.  2012-07-04 09:14:35.165 ObjectiveCTest\[688:f803\] Box number is: 1 
2.  2012-07-04 09:14:35.167 ObjectiveCTest\[688:f803\] Box number is: 2 
3.  2012-07-04 09:14:35.167 ObjectiveCTest\[688:f803\] Box number is: 3 
4.  2012-07-04 09:14:35.167 ObjectiveCTest\[688:f803\] Box number is: 4 
5.  2012-07-04 09:14:35.167 ObjectiveCTest\[688:f803\] Box number is: 5 
6.  2012-07-04 09:14:35.167 ObjectiveCTest\[688:f803\] BoxWarningException The number is above or at 60 
7.  2012-07-04 09:14:35.168 ObjectiveCTest\[688:f803\] Box number is: 6 
8.  2012-07-04 09:14:35.168 ObjectiveCTest\[688:f803\] BoxWarningException The number is above or at 60 
9.  2012-07-04 09:14:35.168 ObjectiveCTest\[688:f803\] Box number is: 7 
10. 2012-07-04 09:14:35.168 ObjectiveCTest\[688:f803\] BoxWarningException The number is above or at 60 
11. 2012-07-04 09:14:35.168 ObjectiveCTest\[688:f803\] Box number is: 8 
12. 2012-07-04 09:14:35.168 ObjectiveCTest\[688:f803\] BoxWarningException The number is above or at 60 
13. 2012-07-04 09:14:35.169 ObjectiveCTest\[688:f803\] Box number is: 9 
14. 2012-07-04 09:14:35.169 ObjectiveCTest\[688:f803\] BoxWarningException The number is above or at 60 
15. 2012-07-04 09:14:35.169 ObjectiveCTest\[688:f803\] Box number is: 10 
16. 2012-07-04 09:14:35.169 ObjectiveCTest\[688:f803\] BoxOverflowException 
17. 2012-07-04 09:14:35.225 ObjectiveCTest\[688:f803\] Box number is: 11

超过10时，SomeOverException异常抛出。

### 3.4 、小于0时的异常 ###

在Box类的setNumber里，当number小于0时，我们抛出普通异常。

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1.  @**try** \{ 
2.   \[box setNumber:-10\]; 
3.   \} 
4.   @**catch** (NSException \*exception) \{ 
5.   NSLog(@"%@",\[exception name\]); 
6.   \} 
7.   @finally \{ 
8.   \[box printNumber\]; 
9.   \}

打印结果：

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1.  2012-07-04 09:17:42.405 ObjectiveCTest\[753:f803\] BoxUnderflowException 
2.  2012-07-04 09:17:42.406 ObjectiveCTest\[753:f803\] Box number is: -10

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