網絡請求的緩存機制cachePolicy 和緩存的清理

- (void)touchesBegan:(NSSet )touches withEvent:(UIEvent )event
{
    //    緩存會自動存到以下這個文件夾中，創建三個文件，其中db文件可以使用數據庫打開
    NSString * tem = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) firstObject];
    NSLog(@"%@", tem);


//    開始請求數據
NSString * path = @"http://localhost/netTest.html";
NSURL * url = [NSURL URLWithString:path];

NSMutableURLRequest * request = [NSMutableURLRequest requestWithURL:url];


//    設置緩存機制，只要這一句代碼就可以了
    request.cachePolicy = NSURLRequestReturnCacheDataElseLoad;

[NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse *response, NSData *data, NSError *connectionError) {

    NSString * str = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
    NSLog(@"%@", str);
}];




//    緩存的清理
    NSURLCache  caches = [NSURLCache sharedURLCache];
    NSCachedURLResponse  response = [caches cachedResponseForRequest:request];
    if (response == nil)
    {
        NSLog(@"沒有緩存");
    }
    else
    {
        NSLog(@"有緩存");
        [caches removeAllCachedResponses];
    }
} </pre>