Objective C 总结（九）：Errors

1. 大多数错误都可以用NSError来进行描述
   

   - (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error;

2. 有时候是按引用传递NSError的

   - (BOOL)writeToURL:(NSURL *)aURL
              options:(NSDataWritingOptions)mask
                error:(NSError **)errorPtr;

       NSError *anyError;
       BOOL success = [receivedData writeToURL:someLocalFileURL
                                       options:0
                                         error:&anyError];
       if (!success) {
           NSLog(@"Write failed with error: %@", anyError);
           // present error to user
       }

3. 生成自定义的错误信息

       NSString *domain = @"com.MyCompany.MyApplication.ErrorDomain";
       NSString *desc = NSLocalizedString(@"Unable to…", @"");
       NSDictionary *userInfo = @{ NSLocalizedDescriptionKey : desc };
    
       NSError *error = [NSError errorWithDomain:domain
                                            code:-101
                                        userInfo:userInfo];

4. Objective-C同样提供了异常处理机制

       @try {
           // do something that might throw an exception
       }
       @catch (NSException *exception) {
           // deal with the exception
       }
       @finally {
           // optional block of clean-up code
           // executed whether or not an exception occurred
       }

   看到有些文档不建议使用异常，有空再研究一下