Question

我正试图像这样访问UIBarButtonItem的框架：

if let items = self.toolbarItems{

        let item = items[1]

        print(item)
        let view = item.value(forKey: "view") as! UIView


    }

print（item）返回现有项目。为什么不能让UIView回来？

Answer 1

使用未记录的属性存在问题。他们可以更改，恕不另行通知。

以下是使用Xcode 8.3.1使用iOS 10 SDK的结果。

let item1 = UIBarButtonItem(customView: UIView())
let view1 = item1.value(forKey: "view") as? UIView
print("\(view1)")

打印

Optional(<UIView: 0x7f9049001400; frame = (0 0; 0 0); layer = <CALayer: 0x60000003cc00>>)

然而

let item2 = UIBarButtonItem(title: "Test", style: .plain, target: nil, action: nil)
let view2 = item2.value(forKey: "view") as? UIView
print("\(view2)")

打印

nil

即使把它提升到新的水平

class MyObject: NSObject { @objc var view: UIView? } // Fake to get selector

let item3 = UIBarButtonItem(title: "Test", style: .plain, target: nil, action: nil)
let view3 = (item3 as NSObjectProtocol).perform(#selector(getter: MyObject.view))?.takeRetainedValue()
print("\(view3)")

打印

nil

获取UIBarButtonItem的帧返回nil

1 个答案: