IOS <2>

 1 static NoteDAO *sharedManager = nil;
 2 + (NoteDAO*)sharedManager {
 3     static dispatch_once_t once;
 4     dispatch_once(&once, ^{
 5          NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
 6          [dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
 7          
 8          NSDate *date1 = [dateFormatter dateFromString:@"2010-08-04 16:01:03"];
 9          Note *note1 = [[Note alloc] init];
10          note1.date = date1;
11          note1.content = @"welcome to MyNote.";
12          NSDate *date2 = [dateFormatter dateFromString:@"2010-08-04 16:01:03"];
13          Note *note2 = [[Note alloc] init];
14          note2.date = date1;
15          note2.content = @"欢迎使用MyNote."; // 设置内容
16          
17         sharedManager = [[self alloc] init];
18         sharedManager.listData = [[NSMutableArray alloc] init];
19         [sharedManager.listData addObject:note1];
20         [sharedManager.listData addObject:note2];
21     });
22        return sharedManager;         
23 }    

　　代码解析：为了获得NoteDAO单例对象

　　NSDateFormatter：相当于NSDate的转换类，将NSDate转换成另一种格式，输出

　　dateFromString方法是将字符串转换成NSDate类型输出，还有一种就是 stringFromDate方法是将NSDate数据转换成字符串格式输出