根据model的对象对应的值（字符串）对model进行排序

//按照拼音首字母对这些Strings进行排序
NSArray *sortDescriptors = [NSArray arrayWithObject:[NSSortDescriptor sortDescriptorWithKey:@"pinYin" ascending:YES]];
[chineseStringsArray sortUsingDescriptors:sortDescriptors];

//根据model里的pinYin对model型的数组排序
NSArray *myary = [chineseStringsArray sortedArrayUsingComparator:^NSComparisonResult(id  obj1, id obj2) {

BookInfo *info1 = obj1;
BookInfo *info2 = obj2;
return (NSComparisonResult)[info1.pinYin compare:info2.pinYin options:NSNumericSearch];
}];
for (BookInfo *info in myary) {
//        NSLog(@"%@",info.pinYin);
[chineseStringsArray1 addObject:info];
}