iOS 处理缓存的三种方法

缓存处理是个相当头疼的事情，要根据需要综合应用不同的策略。总的来说有以下几种情况：

1.URL缓存，例如社交应用的帖子浏览，要在viewDidAppear:里面进行URL缓存。简单来说就是用NSURLCache类，首先在AppDelegate.m里面的

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions；方法里面创建一个NSURLCache的单例：

//设置内存缓存大小
    NSURLCache *URLCache = [[NSURLCache alloc] initWithMemoryCapacity:4 * 1024 * 1024 diskCapacity:10 * 1024 * 1024 diskPath:nil];
    [NSURLCache setSharedURLCache:URLCache];
然后的ViewController.m里面实现方法:

//网络缓存响应方法

- (IBAction)senderButton:(id)sender {

    //天气Api接口
    NSString* path = @"http://www.weather.com.cn/data/sk/101110101.html";
    [self getByURL:path andCallBack:^(id obj) {

    NSString *str = [[NSString alloc]initWithData:obj encoding:NSUTF8StringEncoding];
    NSLog(@"=========================================================\n");
    NSLog(@"post缓存测试：%@",str);
    NSLog(@"=========================================================\n");
    }];

}

//网络请求的内存缓存方法

-(void)getByURL:(NSString *)path andCallBack:(CallBack)callback{

    NSString*  pathStr = [path  stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];

    NSURL *url = [NSURL URLWithString:pathStr];

    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
    [request setCachePolicy:NSURLRequestReloadRevalidatingCacheData];
    NSCachedURLResponse* response = [[NSURLCache sharedURLCache] cachedResponseForRequest:request];

    //判断是否有缓存
    if (response != nil) {
        NSLog(@"有缓存");
        [request setCachePolicy:NSURLRequestReturnCacheDataDontLoad];
    }else{

        NSLog(@"没有缓存");
    }

    //创建NSURLConnection
    NSData* data = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];
    callback(data);

}

2.文件缓存，例如用户信息等基本不会变化的信息保存在本地沙箱

//用户信息缓存用文件保存在沙箱

- (IBAction)userCache:(UIButton *)sender {

    self.UserPath = [self saveFileToDocuments:@"http://www.weather.com.cn/data/sk/101020100.html"];
}

//保存文件到沙箱
- (NSString *)saveFileToDocuments:(NSString *)url
{
    NSString *resultFilePath = @"";

        NSString *destFilePath = [[NSHomeDirectory() stringByAppendingPathComponent:@"Documents"] stringByAppendingPathComponent:url]; // 加上url，组合成本地文件PATH
        NSString *destFolderPath = [destFilePath stringByDeletingLastPathComponent];

        // 判断路径文件夹是否存在不存在则创建
        if (! [[NSFileManager defaultManager] fileExistsAtPath:destFolderPath]) {
            NSLog(@"文件夹不存在，新建文件夹");
            [[NSFileManager defaultManager] createDirectoryAtPath:destFolderPath withIntermediateDirectories:YES attributes:nil error:nil];
        }

        // 判断该文件是否已经下载过
        if ([[NSFileManager defaultManager] fileExistsAtPath:destFilePath]) {
            NSLog(@"文件已下载\n");
            resultFilePath = destFilePath;
        } else {

            NSLog(@"没有缓存，请求数据\n");
            NSData *userInfoData = [NSData dataWithContentsOfURL:[NSURL URLWithString:url]];

            if ([userInfoData writeToFile:destFilePath atomically:YES]) {
                resultFilePath = destFilePath;
            }
        }
    NSData *userInfoData=[[NSFileManager defaultManager] contentsAtPath:resultFilePath];
    NSString* str = [[NSString alloc]initWithData:userInfoData encoding:NSUTF8StringEncoding];

    NSLog(@"=========================================================\n");
    NSLog(@"user:%@",str);
    NSLog(@"=========================================================\n");

    return resultFilePath;
}

3.图片缓存是最重要的，费流量还占内存，所以推荐使用第三方SDWebImage

最简单的就是用这个方法：

[self.imageView sd_setImageWithURL:url completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType, NSURL *imageURL) {
        if (cacheType==SDImageCacheTypeNone) {

            NSLog(@"没有缓存，从网络下载");

        }else if (cacheType==SDImageCacheTypeDisk){

            NSLog(@"有缓存，从磁盘读取");

        }else{

            NSLog(@"有缓存，从内存读取");
        }

    }];

想知道这个方法的内部机制请看这里。

想要demo的去这里下载。

转载请注明出处！