使用NSConnection下載數據

1. 創建NSConnection對象，設置委託對象

NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:[self urlString]]];

[NSURLConnection connectionWithRequest:request delegate:self];

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2. NSURLConnection delegate委託方法

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

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error;

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

- (void)connection DidFinishLoading:(NSURLConnection *)connection;

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3. 實現委託方法

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response {
// store data
    [self.receivedData setLength:0]; //通常在這裏先清空接受數據的緩存
}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
/* appends the new data to the received data */
     [self.receivedData appendData:data];  //可多次收到數據，把新數據添加到現有數據最後面
}

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
// 錯誤處理
}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
// disconnect
        [UIApplication sharedApplication].networkActivityIndicatorVisible = NO;   
        NSString *returnString = [[NSString alloc] initWithData:self.receivedData encoding:NSUTF8StringEncoding];
        NSLog(returnString);
        [self urlLoaded:[self urlString] data:self.receivedData];
        firstTimeDownloaded = YES;
}