iosURLConnectionCache

网络通信层一直是我最重视的技术，因为数据的稳定才能使整个应用流畅运行。

缓存是个双刃剑，用好的就可以增强用户体验，用得不好就会造成一种假象。

首先cache需要用数据库纪录缓存得数据，创建得时间，过期得时间（就是相隔多长时间更新一次缓存），相对应得key。

例如：

FMResultSet*set = [dbexecuteQuery:@"SELECT * FROM json_caches WHERE key = ?",self.cacheName];

if([setnext]) {

NSInteger_id = [setintForColumn:@"row_id"];

jsonData = [setdataForColumn:@"value"];

NSIntegerreadedTimes = [setintForColumn:@"readed_times"];

NSDate*savedTime = [setdateForColumn:@"saved_time"];

NSDate*now = [NSDatedate];

doubletimeInterval = [nowtimeIntervalSinceDate:savedTime];

if(timeInterval <self.cacheValidity*3600) {

BOOLrs = [dbexecuteUpdate:[NSStringstringWithFormat:@"UPDATE json_caches SET readed_times = %d WHERE row_id = %d",++readedTimes,_id]];

NIF_TRACE(@"%d", rs);

}else{

jsonData =nil;

}

当save缓存得时间到现在得时间小于有效缓存时间则说明缓存有效，把缓存数据返回，并且增加一次readtime。

如果没有缓存则重新请求数据

1。首先拼接URL

2.根据url创建request

NSMutableURLRequest*request = [NSMutableURLRequestrequestWithURL:[NSURLURLWithString:self.url]cachePolicy:NSURLRequestReloadIgnoringLocalCacheDatatimeoutInterval:20.f];

3.根据request创建connection

NSURLConnection*conn = [[NSURLConnectionalloc]initWithRequest:requestdelegate:self];

self.connection= conn;

[connrelease];

[self.connectionstart];

4.当建立起connection后就开始接受数据了，会调用connection得委托方法

- (void)connection:(NSURLConnection*)aConnection didReceiveResponse:(NSURLResponse*)response ；

- (void)connection:(NSURLConnection*)aConnection didReceiveData:(NSData*)data ；

- (void)connectionDidFinishLoading:(NSURLConnection*)aConnection ；

5.接受完成后会在finish这个方法里面回调

@try {

jsonValue = [self.bufferyajl_JSON];

}

@catch(NSException * e) {

NIF_ERROR(@"%@",e);

}

}

@finally {

if(self.delegate&& [self.delegaterespondsToSelector:@selector(dURLConnection:didFinishLoadingJSONValue:string:)]) {

NSString*string = [[NSStringalloc]initWithData:self.bufferencoding:NSUTF8StringEncoding];

[self.delegatedURLConnection:selfdidFinishLoadingJSONValue:nilstring:string];

[stringrelease];

}

}

}

}

6.在创建connection得那个类文件中实现协议中得委托方法，然后做相应处理。

7.请求下来得数据会存到数据库中

FMResultSet*set = [dbexecuteQuery:@"SELECT * FROM json_caches WHERE key = ?",self.cacheName,nil];

if([setnext]) { // UPDATE

int_id = [setintForColumn:@"row_id"];

BOOLrs = [dbexecuteUpdate:@"UPDATE json_caches SET value = ?,saved_time = ?,validity_duration=? WHERE row_id = ?", jsonData, [NSDatedate],[NSNumbernumberWithDouble:self.cacheValidity*3600], [NSNumbernumberWithInt:_id]];

NIF_TRACE(@"update cache success? : %d", rs);

}else{

NSError*error =nil;

BOOLrs = [dbexecuteUpdate:@"INSERT INTO json_caches (key,value,saved_time,validity_duration,type) VALUES(?,?,?,?,?)",self.cacheName,jsonData, [NSDatedate], [NSNumbernumberWithDouble:self.cacheValidity*3600],self.cacheType,nil];

NIF_TRACE(@"save cache success? : %d", rs);

if(error) {

NIF_TRACE(@"save cache error happened : %@", error);

}

}

NIF_TRACE(@"---- WRITE TO CACHE %@",self.url);

[dbclose];

8.value是NSData的类型