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タイトルが示すように、NSURLConnectionを介してテーブルビュー画像を非同期で読み込もうとしています。ここでの問題は、下にスクロールすると、テーブルビューに複数の国の同じ旗の画像が読み込まれ、スクロールすると複数の国の異なる旗の画像が読み込まれる傾向があることです（複数の国では同じ旗の画像があります）。バックアップします。非常にゆっくりとスクロールした場合にのみ、国ごとに異なる旗の画像が表示されることに気付きましたが、画像が正しくありません。現時点で何が問題なのかよくわかりません。これが私のコードです：

#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

誰かアイデアはありますか？

4

1 に答える 1

1

どういうわけか、flagImageデータ構造を介してを国名に関連付ける必要があります。

で何が起こっているかを見てみましょう。tableView:cellForRowAtIndexPath: 非同期で画像のリクエストを送信してflagImageから、セルの画像ビューに電流を割り当てます。ただし、NSURLConnectionデリゲートメソッドは、将来の非決定論的な時点で起動し、flagImageその時点で再割り当てされます。

現在行っていることはtableView:cellForRowAtIndexPath:同期では機能しNSURLConnectionますが、非同期デリゲートのコールバックによってトリップします。

于 2012-10-08T19:01:36.547 に答える