registerForActivityResult應在fragment或activity創建之前調用

就是說，如果要為返回的結果注冊監聽器的話，不能在fragment或activity已經創建好了再調用。

可以放在字段中：

class CrimeFragment : Fragment() {
   ...

    private val aLauncher =
        registerForActivityResult(ActivityResultContracts.PickContact()) { uri: Uri? ->
            doWhenChooseSuspect(uri)
        }

    private val requestPermissionLauncher =
        registerForActivityResult(
            ActivityResultContracts.RequestPermission()
        ) { isGranted: Boolean ->
            if (isGranted) {
                aLauncher.launch()
            } else {
                Toast.makeText(
                    context,
                    "we need the permission to get suspect",
                    Toast.LENGTH_LONG
                ).show()
            }
        }
......

文檔有這么一段話：This *must* be called unconditionally, as part of initialization path, typically as a field initializer of an Activity or Fragment.