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从 iPhone 中的 url 加载图像，仅当图像很小时

发布于 2024-07-29 10:52:08 字数 197 浏览 2 评论 0原文

我正在使用 NSData 的 initWithContentsOfURL 从网址加载图像。但是，我事先不知道图像的大小，并且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。

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_畞蕅 2024-08-05 10:52:08

您无法直接通过 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这种操作。如果超出限制，只需向 NSURLConnection 发送取消消息即可停止请求。

简单的例子：（receivedData在头部定义为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

You can't do it directly via NSData however NSURLConnection would support such a thing by loading the image asynchronously and using connection:didReceiveData: to check how much data you have received. If you go over your limit just send the cancel message to NSURLConnection to stop the request.

Simple example: (receivedData is defined in the header as 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

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