如何在不是根Viewcontroller的ViewController上创建一个左右按钮的导航栏？

Question

这就是我想要的样子。我尝试过使用此代码：

let button = UIButton.init(type: .custom)
button.setImage(UIImage.init(named: "yourImageName.png"), for: UIControlState.normal)
button.addTarget(self, action:#selector(ViewController.callMethod), for:.touchUpInside)
button.frame = CGRect.init(x: 0, y: 0, width: 30, height: 30) 
//CGRectMake(0, 0, 30, 30)
let barButton = UIBarButtonItem.init(customView: button)
self.navigationItem.leftBarButtonItem = barButton

但是，当我创建导航控制器时，我将地图视图（主屏幕）设置为导航控制器的根视图控制器。因此，视图将没有默认的后退按钮，因为在它之前的堆栈上没有视图。有没有办法覆盖这个，所以我的图像显示为左按钮？上面的代码不会成功生成左键的图像。它是空白的。

Answer 1

找出答案：

    var image = UIImage(named: "ic-menu-48px.png")
    let navCon = self.navigationController
    image = self.resizeImage(image: image!, targetSize: CGSize(width: 25.0,height: 25.0))
    image = image?.withRenderingMode(.alwaysOriginal)
    self.navigationItem.leftBarButtonItem = UIBarButtonItem(image: image, style:.plain, target: nil, action: nil)


  func resizeImage(image: UIImage, targetSize: CGSize) -> UIImage {
    let size = image.size

    let widthRatio  = targetSize.width  / size.width
    let heightRatio = targetSize.height / size.height

    // Figure out what our orientation is, and use that to form the rectangle
    var newSize: CGSize
    if(widthRatio > heightRatio) {
        newSize = CGSize(width: size.width * heightRatio, height: size.height * heightRatio)
    } else {
        newSize = CGSize(width: size.width * widthRatio,  height: size.height * widthRatio)
    }

    // This is the rect that we've calculated out and this is what is actually used below
    let rect = CGRect(x: 0, y: 0, width: newSize.width, height: newSize.height)

    // Actually do the resizing to the rect using the ImageContext stuff
    UIGraphicsBeginImageContextWithOptions(newSize, false, 1.0)
    image.draw(in: rect)
    let newImage = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()

    return newImage!
}