NSString *string = @"  \n   I Love China ";
    NSLog(@"原始字符串%@",string);
    
    //去掉字符串两端空格
    NSString *str1 = [string stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];
    NSLog(@"去掉字符串两端空格%@",str1);
    
    //去掉字符串两端空格和回车
    NSString *str2 = [string stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet ]];
    NSLog(@"去掉字符串两端空格和回车%@",str2);
    
    //去掉字符串中的空格和回车
    NSMutableString *mutStr = [NSMutableString stringWithString:string];
    
    NSRange range = {0,string.length};
    [mutStr replaceOccurrencesOfString:@" " withString:@"" options:NSLiteralSearch range:range];
    NSRange range2 = {0,mutStr.length};
    
    [mutStr replaceOccurrencesOfString:@"\n"withString:@""options:NSLiteralSearch range:range2];
    NSLog(@"去掉字符串中的空格和回车%@",mutStr);

打印信息

2017-06-26 17:19:45.211 GCDdemo[1718:132780] 原始字符串  
   I Love China 
2017-06-26 17:19:45.211 GCDdemo[1718:132780] 去掉字符串两端空格
   I Love China
2017-06-26 17:19:45.212 GCDdemo[1718:132780] 去掉字符串两端空格和回车I Love China
2017-06-26 17:19:45.213 GCDdemo[1718:132780] 去掉字符串中的空格和回车ILoveChina