xcode出现 use of undeclared identifier

本文探讨了 Xcode 中常见的编译错误 'use of undeclared identifier' 的原因及解决办法,指出这类问题通常是因为遗漏了必要的头文件导致。

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运行为14:42: error: use of undeclared type 'SystemImage' static func loadImage(named: String) -> SystemImage? { ^~~~~~~~~~~ 28:24: error: 'URLSession' is unavailable: This type has moved to the FoundationNetworking module. Import that module to use it. private let session = URLSession.shared ^~~~~~~~~~ Foundation.URLSession:2:18: note: 'URLSession' has been explicitly marked unavailable here public typealias URLSession = AnyObject ^ 50:22: error: use of unresolved identifier 'SystemLabel' private let label = SystemLabel() ^~~~~~~~~~~ 51:26: error: use of unresolved identifier 'SystemImageView' private let imageView = SystemImageView() ^~~~~~~~~~~~~~~ 52:23: error: use of unresolved identifier 'SystemButton' private let button = SystemButton() ^~~~~~~~~~~~ 54:11: error: initializer does not override a designated initializer from its superclass override init(frame: CGRect) { ~~~~~~~~ ^ 49:21: error: use of undeclared type 'SystemView' class PlatformView: SystemView { ^~~~~~~~~~ 55:3: error: 'super' members cannot be referenced in a root class super.init(frame: frame) ^ 60:3: error: 'super' members cannot be referenced in a root class super.init(coder: coder) ^ 67:21: error: use of unresolved identifier 'SystemColor' label.textColor = SystemColor.label ^~~~~~~~~~~ 68:3: error: use of unresolved identifier 'addSubview' addSubview(label) ^~~~~~~~~~ 73:3: error: use of unresolved identifier 'addSubview' addSubview(imageView) ^~~~~~~~~~ 83:3: error: use of unresolved identifier 'addSubview' addSubview(button) ^~~~~~~~~~ 90:3: error: use of unresolved identifier 'NSLayoutConstraint' NSLayoutConstraint.activate([ ^~~~~~~~~~~~~~~~~~ 91:48: error: use of unresolved identifier 'centerXAnchor' imageView.centerXAnchor.constraint(equalTo: centerXAnchor), ^~~~~~~~~~~~~ 92:44: error: use of unresolved identifier 'topAnchor' imageView.topAnchor.constraint(equalTo: topAnchor, constant: 20), ^~~~~~~~~ 97:44: error: use of unresolved identifier 'centerXAnchor' label.centerXAnchor.constraint(equalTo: centerXAnchor), ^~~~~~~~~~~~~ 100:45: error: use of unresolved identifier 'centerXAnchor' button.centerXAnchor.constraint(equalTo: centerXAnchor), ^~~~~~~~~~~~~
07-14
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