android - 如何在 Kotlin 中使用 switch-case 调用 Activity ？

Question

如何在 Kotlin 中使用 switch-case 调用 Activity ？我想在 Kotlin 上使用 switch-case 结构，如下图所示。(Java 代码)

public boolean onNavigationItemSelected(@NonNull MenuItem item) {
        switch (item.getItemId()) {
            case R.id.navigation_home:
                break;
            case R.id.navigation_adminword:
                Intent a = new Intent(activity_callender.this,Words_List.class);
                startActivity(a);
                onStop();
                break;
            case R.id.navigation_myword:
                Intent b = new Intent(activity_callender.this,SaveWords.class);
                startActivity(b);
                onStop();
                break;
            case R.id.navigation_profil:
                Intent c = new Intent(activity_callender.this,UsersActivity.class);
                startActivity(c);
                onStop();
                break;
        }
        return false;
    }

Answer 1

你不能，因为 Java switch 在 Kotlin 中不可用，使用 when 甚至 if case...

fun onNavigationItemSelected(item: MenuItem): Boolean {
    when (item.getItemId()) {
        R.id.navigation_home -> // do something...
        R.id.navigation_adminword -> {
            val a = Intent(this@activity_callender, Words_List::class.java)
            startActivity(a)
            onStop() // this method is called automatically, it is no necessary call it manually
        }
        R.id.navigation_myword -> {
            val b = Intent(this@activity_callender, SaveWords::class.java)
            startActivity(b)
            onStop() // this method is called automatically, it is no necessary call it manually
        }
        R.id.navigation_profil -> {
            val c = Intent(this@activity_callender, UsersActivity::class.java)
            startActivity(c)
            onStop() // this method is called automatically, it is no necessary call it manually
        }
        else -> {
            // else case would be the default switch case
        }
    }
    return false
}

实际上你可以用when做更多的事情，比如返回一个值，然后把它赋值给一个变量，等等...

https://kotlinlang.org/docs/reference/control-flow.html#when-expression