UIView透明渐变 [英] UIView transparent gradient

问题描述

考虑到iOS上的任意UIView，是否有一种方法可以使用Core Graphics（CAGradientLayer）来应用前景透明渐变？

Given an arbitrary UIView on iOS, is there a way using Core Graphics (CAGradientLayer comes to mind) to apply a "foreground-transparent" gradient to it?

我不能使用标准的CAGradientLayer，因为背景比UIColor更复杂。我也无法覆盖PNG，因为背景会随着我的子视图沿其父垂直滚动视图滚动而变化（见图片）。

I can't use a standard CAGradientLayer because the background is more complex than a UIColor. I also can't overlay a PNG because the background will change as my subview is scrolled along its parent vertical scrollview (see image).

我有一个非优雅的后备：让我的uiview剪辑其子视图，并在滚动父滚动视图时移动背景的预渲染渐变png。

I have a non-elegant fallback: have my uiview clip its subviews and move a pre-rendered gradient png of the background as the parent scrollview is scrolled.

推荐答案

这是一个令人尴尬的简单修复：应用CAGradientLayer作为我的子视图的掩码。

This was an embarrassingly easy fix: apply a CAGradientLayer as my subview's mask.

CAGradientLayer *gradientLayer = [CAGradientLayer layer];
gradientLayer.frame = _fileTypeScrollView.bounds;
gradientLayer.colors = [NSArray arrayWithObjects:(id)[UIColor whiteColor].CGColor, (id)[UIColor clearColor].CGColor, nil];
gradientLayer.startPoint = CGPointMake(0.8f, 1.0f);
gradientLayer.endPoint = CGPointMake(1.0f, 1.0f);
_fileTypeScrollView.layer.mask = gradientLayer;

感谢 Cocoanetics 让我指向正确的方向！

Thanks to Cocoanetics for pointing me in the right direction!

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