Iphone 在“集合”视图中加载图像的更快方法
我的UICollectionView有点流量问题。我想显示PDF的缩略图,就像在苹果的iBook应用程序中一样,当我滚动我的收藏视图时,我可以看到它不是很平滑。以下是我加载图片的方式:Iphone 在“集合”视图中加载图像的更快方法,iphone,ios,objective-c,cocoa-touch,Iphone,Ios,Objective C,Cocoa Touch,我的UICollectionView有点流量问题。我想显示PDF的缩略图,就像在苹果的iBook应用程序中一样,当我滚动我的收藏视图时,我可以看到它不是很平滑。以下是我加载图片的方式: - (UICollectionViewCell *)collectionView:(UICollectionView *)cv cellForItemAtIndexPath: (NSIndexPath *)indexPath { GridCell *cell = [cv dequeueReusab
- (UICollectionViewCell *)collectionView:(UICollectionView *)cv cellForItemAtIndexPath: (NSIndexPath *)indexPath
{
GridCell *cell = [cv dequeueReusableCellWithReuseIdentifier:@"gridCell" forIndexPath:indexPath];
...
// Set Thumbnail
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
if ([Tools checkIfLocalFileExist:cell.pdfDoc])
{
UIImage *thumbnail = [Tools generateThumbnailForFile:((PDFDocument *)[self.pdfList objectAtIndex:indexPath.row]).title];
dispatch_async( dispatch_get_main_queue(), ^{
[cell.imageView setImage:thumbnail];
});
}
});
...
return cell;
}
获取缩略图的方法:
+ (UIImage *)generateThumbnailForFile:(NSString *) fileName
{
// ----- Check if thumbnail already exist
NSString* documentsPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];
NSString* thumbnailAddress = [documentsPath stringByAppendingPathComponent:[[fileName stringByDeletingPathExtension] stringByAppendingString:@".png"]];
BOOL fileExists = [[NSFileManager defaultManager] fileExistsAtPath:thumbnailAddress];
if (fileExists)
return [UIImage imageWithContentsOfFile:thumbnailAddress];
// ----- Generate Thumbnail
NSString* filePath = [documentsPath stringByAppendingPathComponent:fileName];
CFURLRef url = (__bridge CFURLRef)[NSURL fileURLWithPath:filePath];
CGPDFDocumentRef documentRef = CGPDFDocumentCreateWithURL(url);
CGPDFPageRef pageRef = CGPDFDocumentGetPage(documentRef, 1);
CGRect pageRect = CGPDFPageGetBoxRect(pageRef, kCGPDFCropBox);
UIGraphicsBeginImageContext(pageRect.size);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextTranslateCTM(context, CGRectGetMinX(pageRect),CGRectGetMaxY(pageRect));
CGContextScaleCTM(context, 1, -1);
CGContextTranslateCTM(context, -(pageRect.origin.x), -(pageRect.origin.y));
CGContextDrawPDFPage(context, pageRef);
// ----- Save Image
UIImage *finalImage = UIGraphicsGetImageFromCurrentImageContext();
NSData *imageData = [NSData dataWithData:UIImagePNGRepresentation(finalImage)];
[imageData writeToFile:thumbnailAddress atomically:YES];
UIGraphicsEndImageContext();
return finalImage;
}
你有什么建议吗?看看。该库非常适合异步图像加载,尤其是方法setImageWithURL:placeholder图像:
您可以调用该方法并使用加载图像或空白png设置占位符,一旦您尝试检索的图像加载,它将填充占位符。这会大大加快你的应用程序速度。你考虑过缓存(存储)缩略图吗?是的,我已经这么做了!谢谢你的图书馆,我来看看。