SwiftUI中ZStack内Color无法覆盖ScrollView内容问题求助

问题描述 #

编写了如下SwiftUI代码，期望顶部的红色色块能完全覆盖ScrollView中的对应区域文本，但实际红色色块呈透明状态，无法遮挡文本，尝试使用渐变也出现同样问题：

ZStack(alignment: .top) {
    Color(red: 1, green: 0, blue: 0, opacity: 1)
    .frame(maxWidth: .infinity, maxHeight: 32)
    
    ScrollView {
        VStack {
            Text("Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.")
        }
    }
}

问题原因 #

ZStack的渲染规则是先添加的元素处于底层，后添加的元素处于上层。当前代码中红色Color是第一个添加的元素，ScrollView在它之后，所以ScrollView会覆盖在红色色块上方，导致文本无法被遮挡。

解决方法 #

方法一：调整元素顺序 #

将红色色块移到ScrollView之后，让它成为上层元素，即可遮挡ScrollView的对应区域：

ZStack(alignment: .top) {
    ScrollView {
        VStack {
            Text("Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.")
        }
    }
    
    Color(red: 1, green: 0, blue: 0, opacity: 1)
        .frame(maxWidth: .infinity, maxHeight: 32)
}

方法二：提升色块层级 #

如果需要保留原有元素顺序，可以给红色色块添加.zIndex(1)属性提升它的渲染层级，让它显示在ScrollView上方：

ZStack(alignment: .top) {
    Color(red: 1, green: 0, blue: 0, opacity: 1)
        .frame(maxWidth: .infinity, maxHeight: 32)
        .zIndex(1)
    
    ScrollView {
        VStack {
            Text("Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.")
        }
    }
}

内容的提问来源于stack exchange，提问作者Abdurakhmon