我刚刚创建了一个UICollectionView
其中用户可以将手机中的图像添加到应用程序的相册功能中。我将图像保存到文档目录中的子目录中,以便可以添加和删除更多图像。但是,当我上下滚动集合视图时,它非常滞后。
怎样才能让滚动条又漂亮又流畅呢?
我的代码:前 16 张图像是预设图像,之后的所有图像都来自文档目录中的子目录
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
CollectionCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"Custom" forIndexPath:indexPath];
//Current index number
int index=indexPath.section * noOfSection + indexPath.row;
//Check if its the preset photos
if(index<16){
NSString *name=[recipePhotos objectAtIndex:indexPath.section * noOfSection + indexPath.row];
cell.imageView.image=[UIImage imageNamed:name];
}
//not preset photos, so retrieve the photos the user added
else {
NSData *data= [NSData dataWithContentsOfFile:[recipePhotos objectAtIndex:index]];
UIImage *theImage=[UIImage imageWithData:data];
cell.imageView.image=theImage;
data=nil;
}
return cell;
}
时间分析器给了我这个
Running Time Self Symbol Name
568.0ms 63.1% 0.0 Main Thread 0x4048
320.0ms 35.5% 0.0 _pthread_start 0x405e
320.0ms 35.5% 0.0 thread_start
320.0ms 35.5% 0.0 _pthread_start
320.0ms 35.5% 0.0 0x1084be960
310.0ms 34.4% 1.0 0x1084be6f0
7.0ms 0.7% 0.0 mach_msg
2.0ms 0.2% 2.0 objc_msgSend
1.0ms 0.1% 1.0 -[NSAutoreleasePool release]
4.0ms 0.4% 0.0 _dispatch_mgr_thread 0x4052
4.0ms 0.4% 0.0 _dispatch_mgr_thread
4.0ms 0.4% 0.0 _dispatch_mgr_invoke
4.0ms 0.4% 4.0 kevent
3.0ms 0.3% 0.0 _dispatch_worker_thread2 0x62b24
3.0ms 0.3% 1.0 start_wqthread
3.0ms 0.3% 0.0 _dispatch_worker_thread2 0x62a84
3.0ms 0.3% 0.0 start_wqthread
3.0ms 0.3% 0.0 _pthread_wqthread
3.0ms 0.3% 0.0 _dispatch_worker_thread2
3.0ms 0.3% 0.0 _dispatch_queue_invoke
3.0ms 0.3% 0.0 _dispatch_queue_drain
3.0ms 0.3% 0.0 _dispatch_client_callout
2.0ms 0.2% 0.0 my_io_execute_passive_block
1.0ms 0.1% 0.0 __86-[NSPersistentUIManager writePublicPlistWithOpenWindowIDs:optionallyWaitingUntilDone:]_block_invoke_0835
1.0ms 0.1% 0.0 -[NSPersistentUIManager writePublicPlistData:]
1.0ms 0.1% 0.0 -[NSURL(NSURLPathUtilities) URLByAppendingPathComponent:]
1.0ms 0.1% 0.0 -[NSURL getResourceValue:forKey:error:]
1.0ms 0.1% 0.0 CFURLCopyResourcePropertyForKey
1.0ms 0.1% 0.0 __block_global_2
1.0ms 0.1% 0.0 -[NSPersistentUIManager writeRecords:withWindowInfos:flushingStaleData:]
1.0ms 0.1% 0.0 _dispatch_call_block_and_release
1.0ms 0.1% 0.0 0x1084b8580
1.0ms 0.1% 0.0 mach_msg_send
1.0ms 0.1% 0.0 mach_msg
1.0ms 0.1% 1.0 mach_msg_trap
1.0ms 0.1% 0.0 _pthread_struct_init 0x62a83
1.0ms 0.1% 0.0 start_wqthread
1.0ms 0.1% 0.0 _pthread_wqthread
1.0ms 0.1% 1.0 _pthread_struct_init
1.0ms 0.1% 0.0 start_wqthread 0x62a7f
您将需要采取一种类似于在表视图中需要执行的方法,您将需要重用视图,就像在表视图中重用单元格一样。
Ray Wenderlich 提供的一个非常好的教程:
在第一部分中,您了解了基础知识,在第二部分中,他们讨论了可重用视图,您看一下链接:
http://www.raywenderlich.com/22417/beginning-uicollectionview-in-ios-6-part-22
Edit
异步加载图像的示例:
在您的单元格中创建一个方法loadImageFromFile
例如,它接收您将这样调用的路径:
[cell loadImageFromFile:[recipePhotos objectAtIndex:index]];
然后看起来像(也许你需要适应一些东西......):
- (void) loadImageFromFile:(NSString*)path{
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, NULL), ^{
NSData *data= [NSData dataWithContentsOfFile:path];
UIImage *theImage=[UIImage imageWithData:data];
dispatch_async(dispatch_get_main_queue(), ^{
cell.imageView.image=theImage;
});
});
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