字符串去掉空格问题

1.去掉两端空格：

[str stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]] ；

2.去掉所有空格：

[str stringByReplacingOccurrencesOfString:@" " withString:@""]  

3.去掉多余空格：

NSString *str = @"    this     is a    test    .   ";

    NSCharacterSet *whitespaces = [NSCharacterSet whitespaceCharacterSet];
    NSPredicate *noEmptyStrings = [NSPredicate predicateWithFormat:@"SELF != ''"];

    NSArray *parts = [str componentsSeparatedByCharactersInSet:whitespaces];
    NSArray *filteredArray = [parts filteredArrayUsingPredicate:noEmptyStrings];
    str = [filteredArray componentsJoinedByString:@" "];