iOS 全局防截屏原理

// 安全窗口内：构建安全容器并挂到窗口上
private func setupSecureContainer() {
    let textField = SecureOverlayTextField(frame: .zero)  // 透明、isSecureTextEntry = true
    guard let secureView = textField.subviews.first else { return }
    secureView.removeFromSuperview()
    secureView.subviews.forEach { $0.removeFromSuperview() }
    secureView.frame = bounds
    secureView.autoresizingMask = [.flexibleWidth, .flexibleHeight]
    secureView.isUserInteractionEnabled = true
    super.addSubview(secureView)   // 安全容器成为窗口唯一直接子视图
    secureTextField = textField    // 强引用保留，避免部分系统版本异常
    secureContentView = secureView
}

// 安全窗口：重写 addSubview，将内容重定向到安全容器
override func addSubview(_ view: UIView) {
    if view === secureContentView {
        super.addSubview(view)
    } else if let content = secureContentView {
        let isRootContent = content.subviews.isEmpty
        if isRootContent {
            view.frame = content.bounds
            view.autoresizingMask = [.flexibleWidth, .flexibleHeight]
        }
        content.addSubview(view)   // 根内容与浮层都加在安全容器内
    } else {
        super.addSubview(view)
    }
}

// 按 tag 查找加在「窗口」上的浮层时，兼容安全窗口
id window = [AppDelegate shared].window;
NSArray<UIView *> *subviewsToSearch = [window isKindOfClass:[SecureWindow class]]
    ? [(SecureWindow *)window subviewsForOverlayTagLookup]
    : [window subviews];

UIView *overlay = nil;
for (UIView *view in subviewsToSearch) {
    if (view.tag == kOverlayTag) {
        overlay = view;
        break;
    }
}
if (overlay) {
    // 执行移除、更新 frame、拖拽逻辑等
}

// 当 inView 为空时，决定 Toast/Loading 加在哪个视图上
func resolveToastContainerView() -> UIView? {
    guard let window = UIApplication.shared.windows.first(where: { $0.isKeyWindow }) else { return nil }
    if window is SecureWindow, let topVC = topViewController(for: window), let v = topVC.view {
        return v   // 安全窗口下用顶层 VC.view，避免加在安全容器内导致渲染异常
    }
    return window
}