ImageView重用上的渐变层 [英] Gradient Layer over ImageView reuse

问题描述

在"cellForRowAtIndexPath"中，我具有以下代码来填充图像(异步)并应用自定义渐变

Within my 'cellForRowAtIndexPath' I have the following code to populate the image (async) and apply a custom gradient

这很好，直到我为每个单元格添加了自定义颜色.当前正在做的是回收以前的颜色，而不是应用新的颜色-这可能是由于以下行将在应用到每个单元格后跳过渐变代码的原因:

This worked fine, until I added a custom colour per cell. What it's currently doing is recycling the previous colour rather than applying a new one - this is presumably due to the following line which will skip the gradient code once applied to each cell:

if(!cell.gradientMask){

但是，如果我将其注释掉，则颜色仍然有效，但是每次添加新图层时，每个单元格上的渐变都会叠加起来(请参阅

However, if I comment this out, the colours work but the gradient on each cell will stack up as a new layer is added each time (see existing issue)

我认为我需要在每次迭代时都删除gradientLayer，这是最好的方法，还是我需要对UIImageView进行子类化?

I presume I need to remove the gradientLayer on each iteration, is that the best approach or perhaps I need to subclass the UIImageView?

if (!cell.gradientMask) {
    gradientMask = [CAGradientLayer layer];
    gradientMask.frame = cell.eventImage.layer.bounds;

    gradientMask.startPoint = CGPointMake(0.5, 0.2);
   gradientMask.endPoint = CGPointMake(0.5, 1.0);


   /* THIS COLOUR CHANGES FOR EACH CELL */
   gradientMask.colors = [NSArray arrayWithObjects:
                       (id)[[UIColor colorWithRed:0.0f green:0.0f blue:1.0f alpha:0.0f] CGColor],

                       (id)[[UIColor colorWithRed:0.0f green:0.0f blue:1.0f alpha:1.0f] CGColor],nil];
    [cell.eventImage.layer insertSublayer:gradientMask atIndex:0];
    cell.gradientMask = gradientMask;
}

推荐答案

您需要在创建渐变蒙版的块外设置颜色:

You need to set the colors outside the block which creates the gradientMask:

if (!cell.gradientMask) {  //Operations that need to be carried out only ONCE are put inside this block
    gradientMask = [CAGradientLayer layer];
    gradientMask.frame = cell.eventImage.layer.bounds;

    gradientMask.startPoint = CGPointMake(0.5, 0.2);
   gradientMask.endPoint = CGPointMake(0.5, 1.0);

    [cell.eventImage.layer insertSublayer:gradientMask atIndex:0];
    cell.gradientMask = gradientMask;
}

//Operations that need to be carried out again and again are outside the block
if (condition1)
{
    cell.gradientMask.colors = [NSArray arrayWithObjects:
                   (id)[[UIColor colorWithRed:0.0f green:0.0f blue:1.0f alpha:0.0f] CGColor],

                   (id)[[UIColor colorWithRed:0.0f green:0.0f blue:1.0f alpha:1.0f] CGColor],nil];
}
else
{
    cell.gradientMask.colors = [NSArray arrayWithObjects:
                   (id)[[UIColor colorWithRed:0.0f green:1.0f blue:0.0f alpha:0.0f] CGColor],

                   (id)[[UIColor colorWithRed:0.0f green:1.0f blue:0.0f alpha:1.0f] CGColor],nil];
}

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