按照字符串的长度排序

  NSSortDescriptor *sortDescriptor;

    sortDescriptor =[[NSSortDescriptor alloc] initWithKey:@"length" ascending:YES];

    NSArray *sortDescriptors = [NSArray arrayWithObject:sortDescriptor];

    NSMutableArray *Arr = [NSMutableArray  arrayWithObjects:@"水电费",@"爱迪adad",@"a",@"b", nil];

    [Arr sortUsingDescriptors:sortDescriptors];