思路：把數組轉化為相應的字符串，看代碼

NSMutableArray *array = [NSMutableArray arrayWithCapacity:self.reciviedContacts.count];

第一種情況

for (ContactModel *model in self.reciviedContacts) {

[array addObject:model.staffid];

}

[para setObject:[array componentsJoinedByString:@","] forKey:@"staffList"];

第二種情況

NSData *jsonData = [NSJSONSerialization dataWithJSONObject:array options:NSJSONWritingPrettyPrinted error:nil];

[para setObject:[[NSString alloc]initWithData:jsonData encoding:NSUTF8StringEncoding] forKey:@"letterFujian"];

// para 是字典專門存放參數的