iOS离线数据缓存读取释放

方法1:一般将服务器第一次返回的数据保存在沙盒里面。这样在手机断网的情况下可以从本地读取数据了。

1.保存到沙盒的代码
+ (void)saveCache:(int)type andID:(int)_id andString:(NSString *)str;  
{  
NSUserDefaults * setting = [NSUserDefaults standardUserDefaults];  
NSString * key = [NSString stringWithFormat:@"detail-%d-%d",type, _id];  
[setting setObject:str forKey:key];  
[setting synchronize];  
 }
读取之前首先根据type和Id判断本地是否有  
+ (NSString *)getCache:(int)type andID:(int)_id  
  {  
 NSUserDefaults * settings = [NSUserDefaults          standardUserDefaults];  
 NSString *key = [NSString stringWithFormat:@"detail-%d-%d",type,  _id];  
   NSString *value = [settings objectForKey:key];  
return value;  
}  
如果沙盒里面有数据
NSString *value = [Tool getCache:5 andID:self.QiuTime];  
    if (value) {  
        NSDictionary *backdict = [value JSONValue];  
        if ([backdict objectForKey:@"items"]) {  
            NSArray *array=[NSArray arrayWithArray:[backdict objectForKey:@"items"]];  
            for (NSDictionary *qiushi in array) {  
                QiuShi *qs=[[[QiuShi alloc]initWithDictionary:qiushi] autorelease];  
                [self.list addObject:qs];  
            }  
        }  
        [self.tableView reloadData];  
     }  
     [self.tableView tableViewDidFinishedLoadingWithMessage:@"数据全部加载完了.."];  
    self.tableView.reachedTheEnd  = YES;  

方法2:使用ASIHTTPRequest和ASIDownloadCache实现本地缓存

 1、设置全局的Cache
在AppDelegate.h中添加一个全局变量
@interface AppDelegate : UIResponder   
 {  
ASIDownloadCache *myCache;  
}  
@property (strong, nonatomic) UIWindow *window;  
@property (nonatomic,retain) ASIDownloadCache *myCache;   
在AppDelegate.m中的- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions方法中添加如下代码
//自定义缓存  
ASIDownloadCache *cache = [[ASIDownloadCache alloc] init];  
self.myCache = cache;  
[cache release];  
 //设置缓存路径  
NSArray *paths =     NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);  
NSString *documentDirectory = [paths objectAtIndex:0];  
[self.myCache setStoragePath:[documentDirectory   stringByAppendingPathComponent:@"resource"]];  
[self.myCache setDefaultCachePolicy:ASIOnlyLoadIfNotCachedCachePolicy];  
 // 在AppDelegate.m中的dealloc方法中添加如下语句
[myCache release];  

到这里为止，就完成了全局变量的声明。

2、设置缓存策略
在实现ASIHTTPRequest请求的地方设置request的存储方式，代码如下
 NSString *str = @"http://....../getPictureNews.aspx";  
 NSURL *url = [NSURL URLWithString:str];  
 ASIHTTPRequest *request = [ASIHTTPRequest requestWithURL:url];  
 //获取全局变量  
AppDelegate *appDelegate = [[UIApplication sharedApplication] delegate];  
//设置缓存方式  
[ request setDownloadCache:appDelegate.myCache];  
//设置缓存数据存储策略，这里采取的是如果无更新或无法联网就读取缓存数据  
[request setCacheStoragePolicy:ASICachePermanentlyCacheStoragePolicy];  
request.delegate = self;  
[request startAsynchronous];  

3、清理缓存数据

我在这里采用的是手动清理数据的方式，在适当的地方添加如下代码，我将清理缓存放在了应用的设置模块：
AppDelegate *appDelegate = [[UIApplication sharedApplication] delegate];  
[appDelegate.myCache clearCachedResponsesForStoragePolicy:ASICachePermanentlyCacheStoragePolicy];