不废话，上代码：
func addCustomBackButton() {
let leftBarBtn = UIBarButtonItem(title: "", style: .plain, target: self,action: #selector(UIViewController.backToPrevious))
leftBarBtn.image = UIImage(named: "backIcon");
leftBarBtn.imageInsets.left = -8;
self.navigationItem.hidesBackButton = true;
self.navigationItem.leftBarButtonItem = leftBarBtn;
}
func backToPrevious(){
if(self.navigationController?.childViewControllers[0] == self){
self.dismiss(animated: true, completion:nil)
return;
}
self.navigationController?.popViewController(animated: true)
}
