一万小时 / iOS下使用本地文件存储应用数据(NSBundle和NSDocumentDirectory)
远没到拼智商的时候
iOS下使用本地文件存储应用数据(NSBundle和NSDocumentDirectory)
在iOS开发中经常会遇到用户数据持久化的问题,一个比较简单的方法是在用户的sandbox 运行环境下使用plist进行存储和读取,这里面有个最常遇到的问题就是有时发你 觉得自己的代码没有问题时,但是就是不能存储成功.
看下面的代码片断.
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| -(void) initManager{ | |
| NSString *path = [self dataFilePath]; | |
| self.credentials = [NSMutableDictionary dictionaryWithContentsOfFile:path]; | |
| } | |
| -(NSString *) dataFilePath{ | |
| NSString *path = [[NSBundle mainBundle] pathForResource:kStoargeFileName ofType:@"plist"]; | |
| return path; | |
| } | |
| -(void)updateStorage:(NSDictionary *)data{ | |
| NSString *path = [self dataFilePath]; | |
| self.credentials = [NSMutableDictionary dictionaryWithDictionary:data]; | |
| NSLog(@"%@", self.credentials); | |
| [self.credentials writeToFile:path atomically:YES]; | |
| } |
乍一看没有任何问题,但是在执行中会发现数据永远都不能存储.
于是我们开始思考可能会是权限的问题,于是在google的帮助下,我们使用了下面的代码:
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| -(void) initManager{ | |
| NSString *path = [self dataFilePath]; | |
| self.credentials = [NSMutableDictionary dictionaryWithContentsOfFile:path]; | |
| } | |
| -(NSString *)dataFilePath{ | |
| NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); | |
| NSString *documentPath = [paths objectAtIndex:0]; | |
| return [documentPath stringByAppendingPathComponent:kStoargeFileName]; | |
| } | |
| -(void)updateStorage:(NSDictionary *)data{ | |
| NSString *path = [self dataFilePath]; | |
| self.credentials = [NSMutableDictionary dictionaryWithDictionary:data]; | |
| NSLog(@"%@", self.credentials); | |
| [self.credentials writeToFile:path atomically:YES]; | |
| } |
然后在执行时,一切都正常了!整个世界安静了.
作为目标是一流程序员的我们当然不甘于只知道how,我们更要知道why.
why
阅读官方文档总是最好的办法, 请看苹果官方文档中关于文件结构的说明:
$home/AppName.app -> 这个就是我们上面代码片断1中的[NSBundle mainBundle],而这个目录是只读. 主要是为了安全考虑.
$home/Docuemnts/ -> 这个就是我们代码片断2中所指向的路径,而此目录正是为了存储应用的数据等信息, 所以在此目录下存储是非常合适.
其它目录说明参考苹果官方文档.