@interface Possession：NSObject<NSCoding>{//遵守NSCoding协议

    NSString *name;//待归档类型


}

@implementation Possession

-(void)encodeWithCoder:(NSCoder *)aCoder{

      [aCoder encodeObject:name forKey:@"name"];


}
-(void)initWithCoder:(NSCoder *)aDecoder{

      name=[[aDeCoder decodeObjectforKey:@"name"] retain];
}

NSString *path = [self possessionArchivePath];

[NSKeyedArchiver archiveRootObject:allPossessions toFile: path ]

allPossessions = [[NSKeyedUnarchiver unarchiveObjectWithFile:path] retain];

NSUserDefaults *defaults =[NSUserDefaults standardUserDefaults];
 NSString *name =@”default string“;
 [defaults setObject:firstName forKey:@"name"];
  //获得UIImage实例

UIImage *image=[[UIImage alloc]initWithContentsOfFile:@"photo.jpg"];

 NSData *imageData = UIImageJPEGRepresentation(image, 100);//UIImage对象转换成NSData

 [defaults synchronize];//用synchronize方法把数据持久化到standardUserDefaults数据库

NSUserDefaults *defaults =[NSUserDefaults standardUserDefaults];
 NSString *name = [defaults objectForKey:@"name"];//根据键值取出name
 NSData *imageData = [defaults dataForKey:@"image"];
 UIImage *Image = [UIImage imageWithData:imageData];//NSData转换为UIImage

NSArray *documentPaths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask,YES);//使用C函数NSSearchPathForDirectoriesInDomains来获得沙盒中目录的全路径。该函数有三个参数，目录类型、he domain mask、布尔值。其中布尔值表示是否需要通过～扩展路径。而且第一个参数是不变的，即为NSSearchPathDirectory 。在iOS中后两个参数也是不变的，即为：NSUserDomainMask 和 YES。
NSString *ourDocumentPath =[documentPaths objectAtIndex:0];

NSString *sandboxPath = NSHomeDirectory();
 // Once you have the full sandbox path, you can create a path from it，但是不能在sandbox的本文件层上写文件也不能创建目录，而应该是此基础上创建一个新的可写的目录，例如Documents,Library或者temp。
NSString *documentPath = [sandboxPath
       stringByAppendingPathComponent:@"Documents"];//将Documents添加到sandbox路径上，具体原因前面分析了！

NSString *FileName=[documentDirectory stringByAppendingPathComponent:fileName];//fileName就是保存文件的文件名

[data writeToFile:FileName atomically:YES];//将NSData类型对象data写入文件，文件名为FileName

NSData data=[NSData dataWithContentsOfFile:FileName options:0 error:NULL];//从FileName中读取出数据

NSArray *documentsPaths=NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask , YES);
 NSString *databaseFilePath=[[documentsPaths objectAtIndex:0] stringByAppendingPathComponent:@"mydb"];
 //上面两句已经比较熟悉了吧！ 
//打开数据库
if (sqlite3_open([databaseFilePath UTF8String], &database)==SQLITE_OK) { 
     NSLog(@"sqlite dadabase is opened."); 
 }
 else{ return;}//打开不成功就返回

char *error; 
 const char *createSql="create table(id integer primary key autoincrement, name text)";
 if (sqlite3_exec(database, createSql, NULL, NULL, &error)==SQLITE_OK) { 
     NSLog(@"create table is ok."); 
 }
 else
 {
    NSLog(@"error: %s",error);
    sqlite3_free(error);//每次使用完毕清空error字符串，提供给下一次使用
} 

const char *insertSql="insert into a person (name) values(‘gg')"; 
if (sqlite3_exec(database, insertSql, NULL, NULL, &error)==SQLITE_OK) { 
     NSLog(@"insert operation is ok."); 
 }

 else
 {
    NSLog(@"error: %s",error);
    sqlite3_free(error);//每次使用完毕清空error字符串，提供给下一次使用
} 

const char *selectSql="select id,name from a person"; 
 sqlite3_stmt *statement; 
 if (sqlite3_prepare_v2(database,selectSql, -1, &statement, nil)==SQLITE_OK) { 
     NSLog(@"select operation is ok."); 
 }
 else
 {
    NSLog(@"error: %s",error);
    sqlite3_free(error);
 } 
 while(sqlite3_step(statement)==SQLITE_ROW) { 
 int _id=sqlite3_column_int(statement, 0); 
 NSString *name=(char*)sqlite3_column_text(statement, 1); 
 NSLog(@"row>>id %i, name %s",_id,name); 
 }
 sqlite3_finalize(statement);

sqlite3_close(database);