你应该在UISearchBar的底部添加一个视图

let rect = searchController.searchBar.frame;
let lineView : UIView = UIView.init(frame: CGRect.init(x: 0, y: rect.size.height-1, width: rect.size.width, height: 1))
lineView.backgroundColor = UIColor.init(hexString: "8CC73E")
searchController.searchBar.addSubview(lineView)

我使用UINavigationBar扩展，使我能够隐藏/显示使用UIAppearance API的阴影或选择哪个导航栏必须隐藏/显示使用故事板(或源代码)的阴影。这是扩展:

import UIKit

private var flatAssociatedObjectKey: UInt8 = 0

/*
  An extension that adds a "flat" field to UINavigationBar. This flag, when
  enabled, removes the shadow under the navigation bar.
 */
@IBDesignable extension UINavigationBar {
    @IBInspectable var flat: Bool {
        get {
            guard let obj = objc_getAssociatedObject(self, &flatAssociatedObjectKey) as? NSNumber else {
                return false
            }
            return obj.boolValue;
        }

        set {
            if (newValue) {
                let void = UIImage()
                setBackgroundImage(void, forBarPosition: .Any, barMetrics: .Default)
                shadowImage = void
            } else {
                setBackgroundImage(nil, forBarPosition: .Any, barMetrics: .Default)
                shadowImage = nil
            }
            objc_setAssociatedObject(self, &flatAssociatedObjectKey, NSNumber(bool: newValue),
                    objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN_NONATOMIC)
        }
    }
}

现在，要禁用所有导航条上的阴影，你必须使用:

UINavigationBar.appearance().flat = true

或者你可以使用故事板启用/禁用此行为:

这里有另一个选择-我认为这只适用于你不需要半透明的导航栏(我没有)。我只是在导航栏的底部添加了一个1像素高的UIView(在导航栏下面1像素)，颜色与我的导航栏相同:

UIView *view = [[UIView alloc] init];
[view setBackgroundColor:self.navigationController.navigationBar.barTintColor];
[self.navigationController.navigationBar addSubview:view];
[view mas_makeConstraints:^(MASConstraintMaker *make) {
    make.height.equalTo(@(1.0f));
    make.leading.trailing.equalTo(self.navigationController.navigationBar);
    make.bottom.equalTo(self.navigationController.navigationBar).offset(1.0f);
}];

我正在使用砌体添加约束。

下面是破解方法。因为它在关键路径上工作，将来可能会崩溃。但就目前而言，它的运作符合预期。

迅速:

self.navigationController?.navigationBar.setValue(true, forKey: "hidesShadow")

Objective - C:

[self.navigationController.navigationBar setValue:@(YES) forKeyPath:@"hidesShadow"];

你应该在UISearchBar的底部添加一个视图

let rect = searchController.searchBar.frame;
let lineView : UIView = UIView.init(frame: CGRect.init(x: 0, y: rect.size.height-1, width: rect.size.width, height: 1))
lineView.backgroundColor = UIColor.init(hexString: "8CC73E")
searchController.searchBar.addSubview(lineView)

编写自己的初始化式:D

import Foundation
import UIKit

extension UINavigationController {
    convenience init(rootViewController : UIViewController, hidesShadow : Bool) {
        self.init(rootViewController : rootViewController)
        self.navigationBar.setValue(hidesShadow, forKey: "hidesShadow")
        if hidesShadow {
            self.extendedLayoutIncludesOpaqueBars = true
            self.navigationBar.isTranslucent = false 
        }
    }
}