iphone - 从 iPhone 中的 url 加载图像，仅在很小的情况下

Question

我正在使用NSData的initWithContentsOfURL从 url 加载图像。但是，我事先不知道图像的大小，如果响应超过一定大小，我希望连接停止或失败。

有没有办法在iPhone 3.0 中做到这一点？

提前致谢。

Answer 1

您不能直接通过 NSData 执行此操作，但是NSURLConnection将通过异步加载图像并使用connection:didReceiveData:检查您收到的数据量来支持此类操作。如果您超出限制，只需将取消消息发送到 NSURLConnection 以停止请求。

简单示例：（receivedData 在 header 中定义为 NSMutableData）

@implementation TestConnection

- (id)init {
    [self loadURL:[NSURL URLWithString:@"http://stackoverflow.com/content/img/so/logo.png"]];
    return self;
}

- (BOOL)loadURL:(NSURL *)inURL {
    NSURLRequest *request = [NSURLRequest requestWithURL:inURL];
    NSURLConnection *conn = [NSURLConnection connectionWithRequest:request delegate:self];

    if (conn) {
        receivedData = [[NSMutableData data] retain];
    } else {
        return FALSE;
    }

    return TRUE;
}

- (void)connection:(NSURLConnection *)conn didReceiveResponse:(NSURLResponse *)response {
    [receivedData setLength:0]; 
}

- (void)connection:(NSURLConnection *)conn didReceiveData:(NSData *)data {
    [receivedData appendData:data];

    if ([receivedData length] > 5120) { //5KB
        [conn cancel];
    }
}

- (void)connectionDidFinishLoading:(NSURLConnection *)conn {
    // do something with the data
    NSLog(@"Succeeded! Received %d bytes of data", [receivedData length]);

    [receivedData release];
}

@end