Undefined symbols for architectu

将原来的UIWebView升级为更轻量级，占用内存更少的WKWebView后，出现了如下的问题：

Undefined symbols for architecture arm64:
  "_OBJC_CLASS_$_WKWebView", referenced from:
  objc-class-ref in DrivingViewController.o
ld: symbol(s) not found for architecture arm64

解决方法 ：在项目配置中添加系统类库：WebKit.framework

1、Go to your Project
2、Select your Target
3、Then, go to Build Phases
4、Open Link Binary With Libraries
5、Finally, just add + the WebKit framework / any other framework.