Ios UICollectionView-如何增加要分配的单元格数
我的UICollectionView有一个非零内容插入集Ios UICollectionView-如何增加要分配的单元格数,ios,objective-c,uicollectionviewcell,Ios,Objective C,Uicollectionviewcell,我的UICollectionView有一个非零内容插入集 self.collectionView.contentInset = UIEdgeInsetsMake(self.mainNavigation.bounds.size.height, 0, 0, 0); MainNavigation是一个透明的导航栏-一旦用户向下滚动,就可以通过MainNavigation部分查看collectionView。由于collectionView的“屏幕上”帧已增加(这些新单元格未排队),因此初始化了更多单
self.collectionView.contentInset = UIEdgeInsetsMake(self.mainNavigation.bounds.size.height, 0, 0, 0);
MainNavigation是一个透明的导航栏-一旦用户向下滚动,就可以通过MainNavigation部分查看collectionView。由于collectionView的“屏幕上”帧已增加(这些新单元格未排队),因此初始化了更多单元格
单元格的初始化非常昂贵,并且会导致UI延迟
我需要的是collectionView最初将更多的单元格加载到内存中,以便初始滚动更平滑
如何增加最初加载的单元格数量?我认为您不需要加载更多单元格,因为这是自然行为。如果你的卷轴不平滑,可能是因为你没有在单元格中正确加载图像 你必须申请签证。例如,您可以这样做(假设您设置了
NSMutableDictionary*imageDic=[[NSMutableDictionary alloc]init];
,您的单元格具有属性@property(非原子,保留)UIImageView*imageView;
,并且您正在使用)
没有办法做到这一点。 您可以做的是:
view.opaque
设置适当的值。它在滚动时提供了良好的性能提升。这是您可以在启用“颜色混合层”选项的情况下在模拟器中调试的内容。您将看到以绿色和红色渲染的命中和未命中- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView_ cellForItemAtIndexPath:(NSIndexPath *)indexPath{
UICollectionViewCell *cell = [collectionView_ dequeueReusableCellWithReuseIdentifier:@"identifier" forIndexPath:indexPath];
NSString* cellKey = [NSString stringWithFormat:@"%d_%d", indexPath.section, indexPath.row];
NSString* imgName = [cellKey stringByAppendingPathExtension:@"jpg"];
NSString *documentsDirectory = [NSSearchPathForDirectoriesInDomains(NSLibraryDirectory, NSUserDomainMask, YES) objectAtIndex:0];
NSString* imagePath = [documentsDirectory stringByAppendingPathComponent:imgName];
BOOL isDirectory = NO;
NSFileManager* fm = [NSFileManager defaultManager];
// set image with image in cache (it will be fast!)
if ([imageDic objectForKey:cellKey])
{
UIImage *img = [imageDic objectForKey:cellKey];
cell.imageView.image = img;
}
// set image with image saved in document directory and put it in cache
else if ([fm fileExistsAtPath:imagePath isDirectory:&isDirectory])
{
UIImage *img = [UIImage imageWithContentsOfFile:imagePath];
cell.imageView.image = img;
[imageDic setObject:img forKey:cellKey];
}
// download image at imageURL, save it and put it in cache too. Until then set image with a placeholder
else
{
__weak UICollectionViewCell* weakCell = cell;
[cell.imageView setImageWithURLRequest:[NSURLRequest requestWithURL:imageURL] placeholderImage:[UIImage imageNamed:@"placeholder"] success:^(NSURLRequest *request, NSHTTPURLResponse *response, UIImage *image) {
weakCell.imageView.image = image;
[weakCell setNeedsLayout];
[imageDic setObject:img forKey:cellKey];
[UIImageJPEGRepresentation(img, 1.f) writeToFile:imagePath atomically:YES];
} failure:^(NSURLRequest *request, NSHTTPURLResponse *response, NSError *error) {
NSLog(@"failed to dl image");
}];
}
return cell;
}