ios - iOS UICollectionViewPerformance 问题

Question

我正在尝试使用具有UIImageView背景的自定义单元格创建一个简单的集合视图。它看起来像：

这是我的代码：

ViewController.m


- (void)viewDidLoad
{
    [super viewDidLoad];
    [self.collectionView registerClass:[MyCell class] forCellWithReuseIdentifier:@"MY_CELL"];
    leftInset = rightInset = 0;
    numberOfDays = 31;

    // Do any additional setup after loading the view, typically from a nib.
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}
-(NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView
{
    return 200;
}
- (NSInteger)collectionView:(UICollectionView *)view numberOfItemsInSection:(NSInteger)section
{
    return numberOfDays;
}

- (UICollectionViewCell *)collectionView:(UICollectionView *)cv cellForItemAtIndexPath:(NSIndexPath *)indexPath;
{
    MyCell *cell = [cv dequeueReusableCellWithReuseIdentifier:@"MY_CELL" forIndexPath:indexPath];

    if(indexPath.row < 10)
    cell.imageView.image = [UIImage imageNamed:@"no"];
    else if(indexPath.section%3==1)
    {
        cell.imageView.image = [UIImage imageNamed:@"ok"];
    }
    else if(indexPath.section%3==2)
    {
        cell.imageView.image = [UIImage imageNamed:@"sa"];
    }
    else{
        cell.imageView.image = [UIImage imageNamed:@"happy_vote"];
    }
    return cell;
}

#pragma mark – UICollectionViewDelegateFlowLayout

- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath {

    return CGSizeMake(CELL_DIM, CELL_DIM);
}

- (UIEdgeInsets)collectionView:
(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout insetForSectionAtIndex:(NSInteger)section {
    // top left bottom right
    return UIEdgeInsetsMake(5, leftInset, 0, 0);
}

我的细胞

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {

        NSLog(@"Init with frame!");
        self.imageView = [[UIImageView alloc] initWithFrame:CGRectMake(0.0, 0.0, frame.size.width, frame.size.height)];

        [self.contentView addSubview:self.imageView];
        [self.imageView setBackgroundColor:[UIColor redColor]];
    }
    return self;
}

它适用于集合视图中的大约 10 个部分。问题是当我想添加更多部分时，垂直滚动开始移动得很慢。我注意到所有单元格都是一次分配的。我正在寻找一种方法来使这对资源更加友好，并让滚动连续移动而不是缓慢和滞后。你能告诉我如何处理资源分配以避免这个问题吗？谢谢你。

PS：我尝试从单元格背景中删除图像视图，并在该方法中cellForItemAtIndexPath:为单元格设置背景颜色，但同样，在 10 个或更多部分之后，它的移动速度非常慢。

Answer 1

为了提高性能，您可能想要做的是检查对象是否已经启动。您还可以单独实例化您的图像，这样就不必每次都从内存中读取它：

使 image1 成为视图控制器的属性：

- (void)viewDidLoad
{
    image1 = [UIImage imageNamed:@"image1"];
    image2 = [UIImage imageNamed:@"image2"];
    image3 = [UIImage imageNamed:@"image3"];
}

- (UICollectionViewCell *)collectionView:(UICollectionView *)cv cellForItemAtIndexPath:(NSIndexPath *)indexPath;
 {
     MyCell *cell = [cv dequeueReusableCellWithReuseIdentifier:@"MY_CELL" forIndexPath:indexPath];

     if(indexPath.row < 10)
     cell.imageView.image = [UIImage imageNamed:@"no"];
     else if(indexPath.section%3==1)
     {
         cell.imageView.image = image1;
     }
     else if(indexPath.section%3==2)
     {
         cell.imageView.image = image2;
     }
     else{
         cell.imageView.image = image3;
     }
     return cell;
}