OC 字符串合并

NSString* result; // 结果字符串
NSString* string1, string2; //已存在的字符串

1. result = [NSString initWithFormat:@"%@,%@", string1, string2 ];
2. result = [string1 stringByAppendingString:string2];
3 . result = [result stringByAppendingFormat:@"%@,%@",string1, string2];