當單元格有UIImageView子視圖時，UITableView體驗波濤洶涌滾動

Question

這讓我在一天中更好的時候發狂。

我有一個UITableView與UIImageViews。這些圖像視圖在tableview的cellForRow函數中加載一個本地保存的PNG文件，並且這種方式可以正常工作，除非tableview停止滾動幾分之一秒，否則當圖像中的一個單元格滾動到可見的位置時可以這麼說。我拖過StackOverflow和谷歌的答案，但我已經來了 - 所以任何幫助將不勝感激。

這裏是我的CellForRow功能代碼：

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { 


    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:@"MyIdentifier"]; 



    if (cell == nil) { 
     cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:@"MyIdentifier"] autorelease]; 
     cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator; 
    } 

    if([currSection isEqualToString:@"composer"]){ 

     MySlide *s = [slidesArray objectAtIndex:indexPath.row]; 

     cell.textLabel.hidden = YES; 
     UIImageView *whiteView = [[UIImageView alloc] initWithFrame:CGRectMake((projectsTable.frame.size.width/2)-150, 4, 204.8, 153.6)]; 

     if([s.slideImage isEqualToString:@""] || s.slideImage == nil){ 
      //no custom image in this cell - go with default background image 

      whiteView.image = [UIImage imageNamed:@"cellback2.png"]; 
      whiteView.backgroundColor = [UIColor whiteColor]; 
     }else{ 
      cell.layer.shouldRasterize = YES; 
      cell.layer.rasterizationScale = [UIScreen mainScreen].scale; 

      NSData *data = [[NSData alloc] initWithContentsOfFile:s.slideImage]; 

      UIImage *im = [[UIImage alloc] initWithData:data]; 


      whiteView.image = im; 

      whiteView.image = [self imageWithImage:whiteView.image CovertToSize:CGSizeMake(204.8,153.6)]; 
      whiteView.backgroundColor = [UIColor whiteColor]; 

     } 


     [cell.contentView addSubview:whiteView]; 

     [whiteView release]; 



     cell.accessoryType = UITableViewCellAccessoryNone; 

    } 


    return cell; 
} 

Answer 1

有一對夫婦的變化來進行，先關當細胞生成時應該添加UIImageView s，而不是每次擊中tableView:cellForRowAtIndexPath:（如@Vishy所示）。其次，您應該緩存您從文檔目錄加載的圖像（[UIImage imageNamed:]會自動爲捆綁資源執行此操作）。

@interface MyViewController() { 

    NSMutableDictionary *_imageCache; 
} 

@end 


@implementation MyViewController 

- (void)viewDidLoad { 
    [super viewDidLoad]; 

    // other viewDidLoad stuff... 

    _imageCache = [[NSMutableDictionary alloc] init]; 
} 

- (void)viewDidUnload { 
    [super viewDidUnload]; 

    // other viewDidUnload stuff... 

    [_imageCache release]; 
    _imageCache = nil; 
} 

- (void)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { 

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:@"MyIdentifier"]; 

    if (cell == nil) { 
     cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:@"MyIdentifier"] autorelease]; 
     cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator; 

     UIImageView *whiteView = [[UIImageView alloc] initWithFrame:CGRectMake((projectsTable.frame.size.width/2)-150, 4, 204.8, 153.6)]; 
     whiteView.tag = 111; 
     whiteView.backgroundColor = [UIColor whiteColor]; 

     [cell.contentView addSubview:whiteView]; 

     [whiteView release]; 
     cell.accessoryType = UITableViewCellAccessoryNone; 
     cell.textLabel.hidden = YES; 
    } 

    UIImageView* iView = (UIImageView*) [cell.contentView viewWithTag:111]; 


    if([currSection isEqualToString:@"composer"]) { 

     MySlide *s = [slidesArray objectAtIndex:indexPath.row]; 

     if([s.slideImage isEqualToString:@""] || s.slideImage == nil) { 

      //no custom image in this cell - go with default background image 
      iView.image = [UIImage imageNamed:@"cellback2.png"]; 
     } 
     else { 

      cell.layer.shouldRasterize = YES; 
      cell.layer.rasterizationScale = [UIScreen mainScreen].scale; 

      // use the image path as the cache key 
      UIImage *theImage = [_imageCache objectForKey:s.slideImage]; 
      if (theImage == nil) { 

       // load the image and save into the cache 
       theImage = [UIImage imageWithContentsOfFile:s.slideImage]; 
       theImage = [self imageWithImage:theImage CovertToSize:CGSizeMake(204.8, 153.6)]; 

       [_imageCache setObject:theImage forKey:s.slideImage]; 
      } 

      iView.image = theImage; 
     } 
    } 
} 

@end 

一般來說，tableView:cellForRowAtIndexPath:是你需要擺脫快速的方法，所以應儘可能避免從磁盤加載圖像。

Answer 2

更改代碼按下面...

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath 
{ 
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:@"MyIdentifier"]; 

if (cell == nil) 
{ 
    cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:@"MyIdentifier"] autorelease]; 
    cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator; 
    UIImageView *whiteView = [[UIImageView alloc] initWithFrame:CGRectMake((projectsTable.frame.size.width/2)-150, 4, 204.8, 153.6)]; 
    whiteView.tag = 111; 
    whiteView.backgroundColor = [UIColor whiteColor]; 

    [cell.contentView addSubview:whiteView]; 

    [whiteView release]; 
    cell.accessoryType = UITableViewCellAccessoryNone; 
    cell.textLabel.hidden = YES; 

} 

UIImageView* iView = (UIImageView*) [cell.contentView viewWithTag:111]; 


if([currSection isEqualToString:@"composer"]) 
{ 
    MySlide *s = [slidesArray objectAtIndex:indexPath.row]; 

    if([s.slideImage isEqualToString:@""] || s.slideImage == nil) 
    { 
     //no custom image in this cell - go with default background image 

     iView.image = [UIImage imageNamed:@"cellback2.png"]; 
    } 
    else 
    { 
     cell.layer.shouldRasterize = YES; 
     cell.layer.rasterizationScale = [UIScreen mainScreen].scale; 

     iView.image = [UIImage imageWithContentsOfFile:s.slideImage]; 
     iView.image = [self imageWithImage:iView.image CovertToSize:CGSizeMake(204.8,153.6)]; 

    } 
    } 
} 

Answer 3

第一次顯示每個UIImage時也有延遲。看到這個職位的詳細信息，促使在緩存時間的工作，而不是顯示時間：

Setting image property of UIImageView causes major lag