如何在代码中使用两个大小类创建UITraitCollection？

Question

我对UITraitCollection有一个简单的扩展

extension UITraitCollection {

    var isIpad: Bool {
        return horizontalSizeClass == .Regular && verticalSizeClass == .Regular
    }
}

以前，我需要为此编写测试(使用TDD)：

let traitCollection = UITraitCollection(verticalSizeClass: .Regular) //the init is either for vertical or horizontal at time
traitCollection.horizontalSizeClass = .Regular //error

XCTAssertTrue(traitCollection.isIpad)

但错误是：

不能分配属性：horizontalSizeClass是一个get唯一属性。

那我该怎么办呢？

Answer 1

好的，我找到了解决办法：

let compactTraitCollection = UITraitCollection(traitsFromCollections: [UITraitCollection(verticalSizeClass: .Compact), UITraitCollection(horizontalSizeClass: .Compact)])
XCTAssertFalse(compactTraitCollection.isIpad)

let regularTraitCollection = UITraitCollection(traitsFromCollections: [UITraitCollection(verticalSizeClass: .Regular), UITraitCollection(horizontalSizeClass: .Regular)])
XCTAssertTrue(regularTraitCollection.isIpad)