when和is的结合:

when (x) {
    is Int -> print(x + 1)
    is String -> print(x.length + 1)
    is IntArray -> print(x.sum())
}

摘自官方文件

使用。

if (myInstance is String) { ... }

或者正好相反

if (myInstance !is String) { ... }

尝试使用名为is的关键字 官方页面参考

if (obj is String) {
    // obj is a String
}
if (obj !is String) {
    // // obj is not a String
}

其他解决方案:KOTLIN

val fragment = supportFragmentManager.findFragmentById(R.id.fragment_container)

if (fragment?.tag == "MyFragment")
{}

你可以这样检查

 private var mActivity : Activity? = null

then

 override fun onAttach(context: Context?) {
    super.onAttach(context)

    if (context is MainActivity){
        mActivity = context
    }

}

你可以用is:

class B
val a: A = A()
if (a is A) { /* do something */ }
when (a) {
  someValue -> { /* do something */ }
  is B -> { /* do something */ }
  else -> { /* do something */ }
}