Question

所以我想要实现的是当用户从UICollectionView点击一个单元格时，来自该单元格的图像显示在下一个UIView上。

为了实现这一点，我使用了委托方法-(void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath和NSUserDefaults。这就是我这样做的方式

获取单元格
从＃1
将图像转换为NSData
将数据放入NSUserDefaults
执行segue到下一个视图控制器
从NSUserDefaults获取数据
转换为UIImage并在UIImageView中显示。

以下是代码：

-(void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath{
    NewsfeedCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"Cell" forIndexPath:indexPath];
    NSData *data = [[NSData alloc]initWithData:UIImagePNGRepresentation(cell.ItemImageView.image)];
    NSLog(@"Before Data %@", data);
    NSUserDefaults *def = [NSUserDefaults standardUserDefaults];
    [def setObject:data forKey:@"feedData"];
    [def synchronize];
    [self performSegueWithIdentifier:@"itemTappedSegue" sender:self];  
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    NSUserDefaults *def = [NSUserDefaults standardUserDefaults];
    NSData *data = [def objectForKey:@"feedData"];
    NSLog(@"After Data:%@", data);
    UIImage *image = [[UIImage alloc]initWithData:data];
    self.imageView.image = image;
}

应该工作但不是。我得到随机结果。有时在下一个UIView中没有图像，有时会有图像，但它不是我拍摄的图像。

编辑::这是cellForItemAtIndexpath

-(UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{
static NSString *CellIdentifier = @"Cell";
NewsfeedCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:CellIdentifier forIndexPath:indexPath];
if(response2.count > 0){
    cell.usernameLabel.text = [self getUsername:[response2 objectAtIndex:indexPath.item]];
    [UIApplication sharedApplication].networkActivityIndicatorVisible =YES;
    dispatch_queue_t getUserAvatar = dispatch_queue_create("Avatar downloader", NULL);
    dispatch_queue_t getFeed = dispatch_queue_create("Feed downloader", NULL);
    dispatch_async(getUserAvatar, ^{
        NSString *urlString = [self getAvatarUrl:[response2 objectAtIndex:indexPath.item]];
        NSURL *url = [[NSURL alloc]initWithString:urlString];
        NSData *avatarData = [NSData dataWithContentsOfURL:url];
        dispatch_async(dispatch_get_main_queue(), ^{
            cell.DPImageView.layer.masksToBounds = YES;
            cell.DPImageView.layer.cornerRadius = 6.0f;
            cell.DPImageView.image = [UIImage imageWithData:avatarData];
        });
    });
    dispatch_async(getFeed, ^{
        NSString *URLString = [self getFeedUrl:[response2 objectAtIndex:indexPath.item]];
        NSURL *URL = [[NSURL alloc]initWithString:URLString];
        NSData *feedData = [NSData dataWithContentsOfURL:URL];
        dispatch_async(dispatch_get_main_queue(), ^{
            cell.ItemImageView.image = [UIImage imageWithData:feedData];
            cell.ItemImageView.layer.masksToBounds = YES;
            cell.LikeBtn.hidden = NO;
            cell.CommentBtn.hidden = NO;
            cell.usernameLabel.hidden = NO;
            cell.DPImageView.hidden = NO;
        });
    });
    [UIApplication sharedApplication].networkActivityIndicatorVisible = NO;
}
else{
    //cell.ItemImageView.image = [UIImage imageNamed:@"NoFeed.png"];
    cell.LikeBtn.hidden = YES;
    cell.CommentBtn.hidden = YES;
    cell.usernameLabel.hidden = YES;
    cell.DPImageView.hidden = YES;
}
return cell;

Answer 1

你为什么这样做：

    NewsfeedCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"Cell" forIndexPath:indexPath];

？您需要获取indexPath的单元格，而不是从池中创建单元格。使用：

NewsFeedCell *cell = [collectionView cellForItemAtIndexPath:indexPath];

相反。

Answer 2

在didSelectItemAtIndexPath:方法中

更改行

-(void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath{
    NewsfeedCell *cell = [collectionView cellForItemAtIndexPath:indexPath]; // put this line in place of creating cell

    NSData *data = [[NSData alloc]initWithData:UIImagePNGRepresentation(cell.ItemImageView.image)];
    NSLog(@"Before Data %@", data);
    NSUserDefaults *def = [NSUserDefaults standardUserDefaults];
    [def setObject:data forKey:@"feedData"];
    [def synchronize];
    [self performSegueWithIdentifier:@"itemTappedSegue" sender:self];  
}

Answer 3

也许你已经解决了这个问题，但我遇到了类似的问题并且发现UICollectionView从0开始。

例如，我的图片被命名为image_1，image_2等。但是，如果我从image_1开始，第一个单元格中就没有任何内容，所以你必须从image_0，image_1开始等等。

希望这有助于任何人。

从UICollectionView中的单元格中获取图像

3 个答案: