ios - UICollectionView 中重复使用的单元格显示多个 UIImageView，而它们应该只显示一个

Question

我的 UICollectionView 有问题。最初它显示良好，显示单元格网格，每个单元格都有一个 UIImageView。这些 UIImageViews 显示存储在应用程序包中的具有透明度的 PNG。

我的问题是，一旦滚动了 UICollectionView，某些单元格似乎已损坏。

损坏的单元格显示多个图像彼此堆叠，最上面的图像是它应该显示的图像，下面的图像是应该在其他单元格中使用的图像。

我最好的猜测是这与重用 UICollectionView 中的单元格的方式有关，但我愿意接受建议。

这是我用于在 UICollectionView 中创建单元格的委托(delegate)代码:

// creates the individual cells to go in the menu view
- (UICollectionViewCell*) collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {

    // create collection view cell
    UICollectionViewCell * cell=[collectionView dequeueReusableCellWithReuseIdentifier:@"cell" forIndexPath:indexPath];

    // create a uiview where we can place all views that need to go into this cell
    UIView * contents=[[UIView alloc] initWithFrame:cell.contentView.bounds];
    [contents setBackgroundColor:[UIColor clearColor]];
    [cell.contentView addSubview:contents];

    // add a button image
    NSString * buttonPath=[[NSBundle mainBundle] pathForResource:@"button" ofType:@"png" inDirectory:[[buttons objectAtIndex:indexPath.row] objectForKey:@"name"]];
    UIImage * button=[UIImage imageWithContentsOfFile:buttonPath];
    UIImageView * buttonView=[[UIImageView alloc] initWithImage:button];
    [buttonView setContentMode:UIViewContentModeScaleAspectFit];
    [buttonView setFrame:contents.bounds];
    [contents addSubview:buttonView];

    // set tag to the indexPath.row so we can access it later
    [cell setTag:indexPath.row];

    // add interactivity
    UITapGestureRecognizer * tap=[[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(onButtonTapped:)];
    [tap setNumberOfTapsRequired:1];
    [cell addGestureRecognizer:tap];

    // return the cell
    return cell;

}

如果需要，我可以提供更多代码。

我怎样才能阻止细胞腐败？

Answer 1

问题是您不断向 UICollectionViewCell 添加 View ，因为它们会被 UICollectionView 自动重复使用。所以旧的 UIImageView 仍然在单元格上，因为您在调用 cellForItemAtIndexPath: 时又添加了一个。

不要使用 addSubview:!

相反，您可以制作一个自定义单元格，其中包含您想要的所有 View 。因此，当调用 cellForItemAtIndexPath: 时，您只需设置此 CustomCollectionViewCell 的内容即可。

这样它肯定不会被损坏。

---

如何构建 CustomCell。

第 1 步:创建 .h 和 .m 类。

自定义单元格.h

#import <UIKit/UIKit.h>

@interface CustomCell : UICollectionViewCell
{
    UIImageView *imageView;
}

@property (nonatomic, retain) UIImageView *imageView; //this imageview is the only thing we need right now.

@end

自定义单元格.m

#import "CustomCell.h"

@implementation CustomCell

@synthesize imageView;

- (id)initWithFrame:(CGRect)aRect
{
    if (self = [super initWithFrame:aRect])
    {
         //we create the UIImageView in this overwritten init so that we always have it at hand.
         imageView = [UIImageView alloc] init];
         //set specs and special wants for the imageView here.
         [self addSubview:imageView]; //the only place we want to do this addSubview: is here!

         //You wanted the imageView to react to touches and gestures. We can do that here too.
         UITapGestureRecognizer * tap=[[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(onButtonTapped:)];
        [tap setNumberOfTapsRequired:1];
        [self addGestureRecognizer:tap];


        //We can also prepare views with additional contents here!
        //just add more labels/views/whatever you want.
    }
    return self;
}

-(void)onButtonTapped:(id)sender
{
    //the response to the gesture.
    //mind that this is done in the cell. If you don't want things to happen from this cell.
    //then you can still activate this the way you did in your question.

}

第 2 步:导入它!现在我们已经创建了 CustomCell，我们可以将它导入到我们想要使用它的类中。

第 3 步:实际使用它!

// creates the individual cells to go in the menu view
- (CustomCell*) collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {

    // create collection view cell
    CustomCell *cell = (CustomCell *)[collectionView dequeueReusableCellWithReuseIdentifier:@"CustomCell" forIndexPath:indexPath]; //this is the place where the CustomCell does his magic.
    //Make sure to use the CustomCellReuseId that you register in the viewdidload/loadview (step4)

    // add a button image
    NSString * buttonPath=[[NSBundle mainBundle] pathForResource:@"button" ofType:@"png" inDirectory:[[buttons objectAtIndex:indexPath.row] objectForKey:@"name"]];

    cell.imageView.image = [UIImage imageWithContentsOfFile:buttonPath]; //place the image on the CustemCell.imageView as we prepared.

    // set tag to the indexPath.row so we can access it later
    [cell setTag:indexPath.row]; //we don't need this to access the cell but I left this in for your personal want.

/*
 * we can now do this from the CustomCell as well!
 *
    // add interactivity
    UITapGestureRecognizer * tap=[[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(onButtonTapped:)];
    [tap setNumberOfTapsRequired:1];
    [cell addGestureRecognizer:tap];
*/
    // return the cell
    return cell;

}

Step4:将cell注册到collectionView

在 viewDidLoad/loadView 添加这一行:

[_collectionView registerClass:[CustomCell class] forCellWithReuseIdentifier:@"CustomCell"];

第 5 步:享受吧!您的 CustomCell 已完成。现在随心所欲，别忘了喝点咖啡。