Question

我正在使用NSData dataWithContentsOfURL方法在tableview中显示图像，但是当我滚动tableview GUI时，hanged.so在搜索论坛后发现我可以尝试使用NSUrlConnection方法。所以我试过但我无法成功实现它。

请在下面找到我的代码......

请帮助我，我怎么能正确地做到这一点..

// Customize the appearance of table view cells.
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath 
{
    static NSString *CellIdentifier = @"Cell";

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];

    if (cell == nil)
    {
        cell = [[[UITableViewCell alloc] initWithFrame:CGRectZero reuseIdentifier:@"DataIdentifier"]  autorelease];

        cell.selectionStyle = UITableViewCellSelectionStyleNone;
        cell.backgroundColor = [UIColor colorWithRed:230.0/255.0 green:249.0/255.0 blue:230.0/255.0 alpha:2.0];

        cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator;

        profileName = [appDelegate.arrCommunityUserList objectAtIndex:indexPath.row];

        NSString *imgName = [profileName.user_image stringByTrimmingCharactersInSet: [NSCharacterSet whitespaceAndNewlineCharacterSet]];

        NSString *strValue = [NSString stringWithFormat:@"%d", profileName.userID];

        if (tableView == myTableView)
        {
            cellRectangle = CGRectMake(15, 2, 75, 75 );

            NSString *myurl = [NSString stringWithFormat: @"%@pics/photos/%@/%@",ConstantImgURL, strValue,imgName];

            NSURL *url = [NSURL URLWithString: myurl];

            imageView = [[UIImageView alloc] initWithFrame: cellRectangle];

            NSURLRequest *request = [[NSURLRequest alloc] initWithURL:[NSURL URLWithString:myurl]];
            [NSURLConnection connectionWithRequest:request delegate:self];

            // create the connection with the request
            // and start loading the data
            NSURLConnection *theConnection =[[NSURLConnection alloc] initWithRequest:
                                             request delegate:self];

            if (theConnection) 
            {
                receivedData = [[NSMutableData data] retain];

            } 

            [cell.contentView addSubview:imageView];

        }


    }

return cell;    
}

// did receive response
- ( void )connection:( NSURLConnection * )connection didReceiveResponse:( NSURLResponse * )response 
//--------------------------------------------------------------------------------------------------
{  
    NSLog(@"Received response: %@", response);
}

// get recieved data
- ( void )connection:( NSURLConnection * )connection didReceiveData:( NSData * )data 
//----------------------------------------------------------------------------------
{  
    //  NSLog(@"Connection received data, retain count: %d", [connection retainCount]);

    [receivedData appendData:data]; 

}  

// finished loading 
- ( void )connectionDidFinishLoading:( NSURLConnection * )connection 
//-------------------------------------------------------------------
{  
    // Set appIcon and clear temporary data/image
    UIImage *image = [[UIImage alloc] initWithData:receivedData];
    imageView.image = image;



}  

// connection failed with error
- ( void )connection:( NSURLConnection * )connection didFailWithError:( NSError * )connError 
//---------------------------------------------------------------------------------------
{
    //  NSLog(@"Error receiving response: %@", connError);
    [connection release];
    [receivedData release];
}

Answer 1

dataWithContentsOfURL是同步网络请求。这意味着在调用代码的地方，它将等待请求完成，然后再继续执行下一条指令。同步网络不好。特别糟糕。它只能用于测试。

您应该做的是为这些图像触发异步请求。上面的代码非常慢的原因是tableView每次要求cellForRowAtIndexPath:的dataSource委托;您的代码会同步触发网络请求 - 这意味着在图像的网络请求完成之前，不会返回单元格。

相反，您应该做的是在请求tableView时异步加载所有图像。 Here's a good example使用标记在返回时标识它们。在你正在做的事情的整个背景下，这并不容易;所以也许您可能希望在显示tableView时启动所有NSURLConnections，为0返回numberOfSectionsInTableView直到连接完成，然后在reloadData上调用tableView当它们全部完成时（并使numberOfSectionsInTableView现在返回要显示的正确行数）。

Answer 2

开始使用ASI库：http://allseeing-i.com/ASIHTTPRequest/How-to-use 越快越好。

Answer 3

我认为这可能会解决您的问题... http://www.markj.net/iphone-asynchronous-table-image/

NSURLConnection，tableview GUI挂起

3 个答案: