iOS 开发指南 第11章 数据持久化之属性列表 学习

1 概述

沙箱目录：一种安全策略，原理是只能允许自己的应用访问目录，而不许其他应用访问。

子目录：Documents 用于储存非常大的文件或需要非常频繁更新的数据

NSArray ＊documentDirectory＝NSSearchPathForDirectoriesInDomains（NSDocumentDirectory，NSUserDomainMask，YES）；

documentDirectory是只有一个元素的数组，还需要取出路径

NSString ＊myDocPath＝［documentDirectory objectAtIndex：0］；

Library Preferences用于存放应用程序的设置数据 Caches用于存放缓存文件

tmp 临时文件目录 NSString ＊temDirectory＝NSTemporaryDirectory（）；

2 持久化方式 数据储存方式

属性列表：是XML文件，数组和字典可以与属性列表文件相互转换。

NSArray和NSDictionary提供了读写属性列表文件的方法：＋array/dictionaryWithContentsOfFile：

－initWithContentOfFile：

writeToFile：atomically：是否使用辅助文件

获取文件代码：

- (NSString *)applicationDocumentsDirectoryFile {获取沙箱Documents目录文件的完整路径
    NSString *documentDirectory = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
    NSString *path = [documentDirectory stringByAppendingPathComponent:@"NotesList.plist"];

    return path;
}
- (void)createEditableCopyOfDatabaseIfNeeded {

    NSFileManager *fileManager = [NSFileManager defaultManager];
    NSString *writableDBPath = [self applicationDocumentsDirectoryFile];获取文件目录
    判断文件是否存在：fileExistsAtPath：
    BOOL dbexits = [fileManager fileExistsAtPath:writableDBPath];
    if (!dbexits) {若不存在则复制一个
        NSString *defaultDBPath = [[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:@"NotesList.plist"];

        NSError *error;
        BOOL success = [fileManager copyItemAtPath:defaultDBPath toPath:writableDBPath error:&error];
        NSAssert(success, @"错误写入文件");断言函数，第一个参数为假时抛出异常
    }
}

读取与写入文件代码：程序的插入／删除／查询等无非是文件的操作

//插入Note方法
-(int) create:(Note*)model
{
    NSString *path = [self applicationDocumentsDirectoryFile];
    NSMutableArray *array = [[NSMutableArray alloc] initWithContentsOfFile:path];

    NSDateFormatter *dateFormat = [[NSDateFormatter alloc] init];
    [dateFormat setDateFormat: @"yyyy-MM-dd HH:mm:ss"];
    将传入的数据封装成文件所需格式
    NSDictionary* dict = [NSDictionary
                          dictionaryWithObjects:@[[dateFormat stringFromDate: model.date],model.content]
                          forKeys:@[@"date",@"content"]];
    ＊setValue：forKey：    ＊
    [array addObject:dict];

    [array writeToFile:path atomically:YES];

    return 0;
}

//删除Note方法
-(int) remove:(Note*)model
{
    NSString *path = [self applicationDocumentsDirectoryFile];
    NSMutableArray *array = [[NSMutableArray alloc] initWithContentsOfFile:path];

    for (NSDictionary* dict in array) {

        NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
        [dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
        是把value取出来而不是key比较
        //Note* note = [[Note alloc] init];
        NSDate *date = [dateFormatter dateFromString:[dict objectForKey:@"date"]];
        //note.content = [dict objectForKey:@"content"];

        //比较日期主键是否相等
        if ([date isEqualToDate:model.date]){
            [array removeObject: dict];
            [array writeToFile:path atomically:YES];
            break;
        }
    }

    return 0;
}

//修改Note方法
-(int) modify:(Note*)model
{

    NSString *path = [self applicationDocumentsDirectoryFile];
    NSMutableArray *array = [[NSMutableArray alloc] initWithContentsOfFile:path];

    for (NSDictionary* dict in array) {

        NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
        [dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];

        NSDate *date = [dateFormatter dateFromString:[dict objectForKey:@"date"]];
        NSString* content = [dict objectForKey:@"content"];

        //比较日期主键是否相等
        if ([date isEqualToDate:model.date]){
            [dict setValue:content forKey:@"content"];
            [array writeToFile:path atomically:YES];
            break;
        }
    }
    return 0;
}

//查询所有数据方法
-(NSMutableArray*) findAll
{
    NSString *path = [self applicationDocumentsDirectoryFile];

    //[self.listData removeAllObjects];
    NSMutableArray *listData = [[NSMutableArray alloc] init];

    NSMutableArray *array = [[NSMutableArray alloc] initWithContentsOfFile:path];

    for (NSDictionary* dict in array) {

        NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
        [dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];

        Note* note = [[Note alloc] init];
        note.date = [dateFormatter dateFromString:[dict objectForKey:@"date"]];
        note.content = [dict objectForKey:@"content"];

        [listData addObject:note];

    }
    return listData;
}

//按照主键查询数据方法
-(Note*) findById:(Note*)model
{
    NSString *path = [self applicationDocumentsDirectoryFile];
    NSMutableArray *array = [[NSMutableArray alloc] initWithContentsOfFile:path];

    for (NSDictionary* dict in array) {

        NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
        [dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];

        Note* note = [[Note alloc] init];
        note.date = [dateFormatter dateFromString:[dict objectForKey:@"date"]];
        note.content = [dict objectForKey:@"content"];

        //比较日期主键是否相等 日期字段是主键
        if ([note.date isEqualToDate:model.date]){
            return note;
        }
    }
    return nil;
}