延遲加載的UIScrollView - 如何在一個滾動視圖這樣滾動平滑

我已經完成延遲加載：延遲加載的UIScrollView - 如何在一個滾動視圖這樣滾動平滑

-(void)scrollViewDidScroll:(UIScrollView *)myScrollView { 

    int currentPage = (1 + myScrollView.contentOffset.x/kXItemSpacingIphone); 
    for (ItemView* itemView in [self.itemRow subviews]){ 
     if (itemView.tag >= currentPage-2 && itemView.tag <= currentPage+2) 
     { 
      //keep it visible 
      if (!itemView.isLoaded) { 
       [itemView layoutWithData:[self.items objectAtIndex:itemView.tag-1]]; 
      } 
     } 
     else 
     { 
      //hide it 
      if (itemView.isLoaded) { 
       [itemView unloadData]; 
      } 

     } 
    } 
}

基本上裝載的觀點，如果它是+/- 2「頁」被在屏幕上。這大大減少了我正在使用的內存量（而不是一次加載20多個ItemViews），這很好。但是，所有加載/卸載都會使滾動變得有點波動，特別是在較慢的設備上。下面是實際發生的ItemView控件加載：

- (void)layoutWithData:(Item*)_data { 
    self.data = _data; 

//grab the image from the bundle 
    UIImage *img; 
    NSString *filePath = [[NSBundle mainBundle] pathForResource:_data.image ofType:@"jpg"]; 
     if(filePath.length > 0 && filePath != (id)[NSNull null]) { 
      img = [UIImage imageWithContentsOfFile:filePath]; 
     } 

    UIButton *btn = [UIButton buttonWithType:UIButtonTypeCustom]; 
    [btn setImage:img forState:UIControlStateNormal]; 
    [btn addTarget:self action:@selector(tapDetected:) forControlEvents:UIControlEventTouchUpInside]; 
    btn.frame = CGRectMake(0, 0, kItemPosterWidthIphone, kItemPosterHeightIphone); 
    [self addSubview:btn]; 

    self.isLoaded = YES; 

}

而且ItemView控件卸載：

- (void)unloadData{ 
    for(UIView *subview in [self subviews]) { 
     [subview removeFromSuperview]; 
    } 
    self.data = nil; 
    self.isLoaded = NO; 
}

同樣，我能做些什麼，使加載/卸載速度更快，因此UIScrollView的更順暢？

嘗試異步：

- (void)layoutWithData:(Item*)_data { 
    self.data = _data; 
    self.isLoaded = YES; 

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0), ^{ 
     UIImage *img; 
     NSString *filePath = [[NSBundle mainBundle] pathForResource:_data.image ofType:@"jpg"]; 
      if(filePath.length > 0 && filePath != (id)[NSNull null]) { 
       img = [UIImage imageWithContentsOfFile:filePath]; 
      } 

     dispatch_async(dispatch_get_main_queue(), ^{ 
      UIButton *btn = [UIButton buttonWithType:UIButtonTypeCustom]; 
      [btn setImage:img forState:UIControlStateNormal]; 
      [btn addTarget:self action:@selector(tapDetected:) forControlEvents:UIControlEventTouchUpInside]; 
      btn.frame = CGRectMake(0, 0, kItemPosterWidthIphone, kItemPosterHeightIphone); 
      self.imageView = btn; 
      [self addSubview:btn]; 


     }); 

    }); 
}

來源

2012-10-10 soleil