设置Alpha作为UIScrollVIew的子视图的UIView非常慢 [英] setting Alpha for UIView that is a subview of UIScrollVIew very slow

问题描述

当我尝试时，我有 UIScrollView 包含几个 UIView
setAlpha：对于 UIView 之一，我得到1.5秒的延迟，直到 UIView alpha

I have UIScrollView that contains several UIView when I try to setAlpha: for one of the UIView, I get 1.5 second delay till the UIView alpha is set.

这里是
setContentOffset 下面的代码在 setAlpha：，尽管 setAlpha：之前是用代码编写的

Here is the code below setContentOffset does run before the setAlpha: although the setAlpha: is written before in code

-(void)setAlphaForIndex:(int)Index{

    for (UIView *v in imgScroll.subviews){

        if (v.tag == Index) {
            [v setAlpha:0.6];
            if (![self checkIfImageInScrollRange:Index]){
                if (v.tag < 5)
                    [imgScroll setContentOffset:CGPointMake(0, 0) animated:YES];
                else
                    [imgScroll setContentOffset:CGPointMake((Index - 5) * (CELLWIDTH) + (Index - 5 - 1) * 3, 0) animated:YES];
            }
        } else {
            [v setAlpha:1.0];
        }
    }
}

推荐答案

再次遍历代码。

看起来您可以只使用循环
设置Alpha，然后再设置contentOffset

It looks like you could use the loop only for setting alpha and set the contentOffset later.

代码应为：

-(void)setAlphaForIndex:(int)Index {

    for (UIView *v in imgScroll.subviews) {

        if (v.tag == Index) 
            [v setAlpha:0.6];
        else
            [v setAlpha:1.0];
    }

    if (![self checkIfImageInScrollRange:Index]){
      if (Index < 5)
        [imgScroll setContentOffset:CGPointMake(0, 0) animated:YES];
      else
        [imgScroll setContentOffset:CGPointMake((Index - 5) * (CELLWIDTH) + (Index - 5 - 1) * 3, 0) animated:YES];
    }
}

因为始终只有一个带有alpha 0.6的视图b $ b可以避免循环并提高性能。

Since there is always only one view with alpha 0.6 you can avoid the loop and improve performance.

添加一个名为transparentViewIndex的整数属性并将
初始化为-1。改进后的代码如下所示：

Add an integer property called transparentViewIndex and initialize it to -1. Improved code would then look like:

-(void)setAlphaForIndex:(int)Index{

  if (self.transparentViewIndex > -1) [[imgScroll viewWithTag: transparentViewIndex] setAlpha:1.0];

  [[imgScroll viewWithTag: Index] setAlpha:0.6];

  self.transparentViewIndex = Index;

  if (![self checkIfImageInScrollRange:Index]){
    if (Index < 5)
      [imgScroll setContentOffset:CGPointMake(0, 0) animated:YES];
    else
      [imgScroll setContentOffset:CGPointMake((Index - 5) * (CELLWIDTH) + (Index - 5 - 1) * 3, 0) animated:YES];
  }
}

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