kotlin passes the function as a parameter into the call, such as::

High-level usage of kotlin, you can pass a function as a parameter into another function to call,

1. Use :: to pass in functions, functions with parameters and return values, such as:

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        viewModel = ViewModelProvider(this).get(MainViewModel::class.java)
        // TODO: Use the ViewModel

        // 传入函数参数
        printFather(::printSon, "father")
    }

    /**
     * 定义一个函数参数
     */
    private fun printFather(method: (String) -> String, str: String) {
        Log.d("Alex", str)
        Log.d("Alex", method("son"))
        // 调用函数的invoke()是一样的
        Log.d("Alex", method.invoke("son"))
    }

    private fun printSon(str: String): String {
        return str
    }

Print result:

2023-04-11 08:56:58.273 22645-22645 Alex                    com.example.myapplication2           D  father
2023-04-11 08:56:58.273 22645-22645 Alex                    com.example.myapplication2           D  son
2023-04-11 08:56:58.273 22645-22645 Alex                    com.example.myapplication2           D  son
 

Use :: to pass in functions, functions without parameters and return values, such as:

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        viewModel = ViewModelProvider(this).get(MainViewModel::class.java)
        // TODO: Use the ViewModel

        // 传入函数参数
        printFather(::printSon, "father")
    }

    /**
     * 定义一个函数参数
     */
    private fun printFather(method: () -> Unit, str: String) {
        Log.d("Alex", str)
        method()
        // 调用函数的invoke()是一样的
        method.invoke()
    }

    private fun printSon() {
        Log.d("Alex", "son")
    }

Print result:

2023-04-11 08:52:54.065 22542-22542 Alex                    com.example.myapplication2           D  father
2023-04-11 08:52:54.065 22542-22542 Alex                    com.example.myapplication2           D  son
2023-04-11 08:52:54.065 22542-22542 Alex                    com.example.myapplication2           D  son