正如标题所暗示的，我正在尝试通过 NSURLConnection 异步加载 tableview 图像。这里的问题是，当我向下滚动时，我的 tableview 倾向于在 tableview 中为多个国家/地区加载相同的标志图像，然后在滚动时为多个国家/地区加载不同的标志图像（因为在多个国家/地区具有相同的标志图像）备份。我注意到，只有当我滚动得很慢时，我才能获得不同国家/地区的不同旗帜图像，但图像不正确。我不太确定目前的问题是什么。这是我的代码：
#import "ViewController.h"
@implementation ViewController
@synthesize tableView;
@synthesize countryNamesArray;
@synthesize receivedData;
@synthesize flagImage;
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
// Release any cached data, images, etc that aren't in use.
}
#pragma mark - View lifecycle
- (void)viewDidLoad
{
countryNamesArray=[[NSArray alloc] initWithObjects:@"India",@"USA",@"Antarctica",@"Brazil",@"Canada",@"China",@"France",@"Germany",@"Italy",@"Japan",@"Kenya",@"Malaysia",@"Mexico",@"South Africa",@"United Kingdom",@"Vietnam",nil];
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
}
- (void)viewDidUnload
{
[super viewDidUnload];
// Release any retained subviews of the main view.
// e.g. self.myOutlet = nil;
}
- (void)viewWillAppear:(BOOL)animated
{
[super viewWillAppear:animated];
}
- (void)viewDidAppear:(BOOL)animated
{
[super viewDidAppear:animated];
}
- (void)viewWillDisappear:(BOOL)animated
{
[super viewWillDisappear:animated];
}
- (void)viewDidDisappear:(BOOL)animated
{
[super viewDidDisappear:animated];
}
- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
// Return YES for supported orientations
if ([[UIDevice currentDevice] userInterfaceIdiom] == UIUserInterfaceIdiomPhone) {
return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown);
} else {
return YES;
}
}
-(NSInteger)tableView:(UITableView *)tableview numberOfRowsInSection:(NSInteger)section{
return 16;
}
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
// This method is called when the server has determined that it
// has enough information to create the NSURLResponse.
// It can be called multiple times, for example in the case of a
// redirect, so each time we reset the data.
// receivedData is an instance variable declared elsewhere.
[receivedData setLength:0];
}
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
// Append the new data to receivedData.
// receivedData is an instance variable declared elsewhere.
[receivedData appendData:data];
}
- (void)connection:(NSURLConnection *)connection
didFailWithError:(NSError *)error
{
// release the connection, and the data object
// receivedData is declared as a method instance elsewhere
// inform the user
NSLog(@"Connection failed! Error - %@ %@",
[error localizedDescription],
[[error userInfo] objectForKey:NSURLErrorFailingURLStringErrorKey]);
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
// do something with the data
// receivedData is declared as a method instance elsewhere
NSLog(@"Succeeded! Received %d bytes of data",[receivedData length]);
flagImage = [UIImage imageWithData: receivedData];
}
-(void)issueRequest:(NSString *)fullCountryImageURL{
NSURLRequest *theRequest=[NSURLRequest requestWithURL:[NSURL URLWithString:fullCountryImageURL]
cachePolicy:NSURLRequestUseProtocolCachePolicy
timeoutInterval:60.0];
// create the connection with the request
// and start loading the data
NSURLConnection *theConnection=[[NSURLConnection alloc] initWithRequest:theRequest delegate:self];
if (theConnection) {
// Create the NSMutableData to hold the received data.
// receivedData is an instance variable declared elsewhere.
receivedData = [NSMutableData data];
}
else {
// Inform the user that the connection failed.
}
}
-(UITableViewCell *) tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath{
static NSString *cellIdentifier = @"countryCell";
UITableViewCell *cell=(UITableViewCell *) [self.tableView dequeueReusableCellWithIdentifier:cellIdentifier];
if (cell==nil){
cell=[[UITableViewCell alloc] initWithStyle: UITableViewCellStyleSubtitle reuseIdentifier:cellIdentifier];
}
// Create the request.
NSString *flagImageURLPartOne = @"http://www.flagimage.com/";
NSString *countryNumber = [NSString stringWithFormat:@"%i", indexPath.row+1];
NSString *flagImageURLPartTwo = @".png";
NSString *fullCountryImageURL = [NSString stringWithFormat:@"%@%@%@", flagImageURLPartOne, countryNumber, flagImageURLPartTwo];
[self issueRequest:fullCountryImageURL];
cell.imageView.image = flagImage;
cell.textLabel.text= [countryNamesArray objectAtIndex:indexPath.row];
return cell;
}
-(void) tableView:(UITableView *) tableview didSelectRowAtIndexPath:(NSIndexPath *)indexPath{
}
@end
有人有想法么？