常連

### 前提
C言語は勉強済み
Kotlinを勉強し始めたばかりで、長澤太郎 著「Kotlinスタートブック」を見ながら勉強しています。
ある団体でアプリを作成しようとしているのですが、そのログイン画面を作ろうとしています。

### 伺いたいこと
Android StudioのLogin_activityのファイル「LoginActivity.kt」のコードを解読しているのですが、本には記載されていないコード（11行目のsuperなど）があり、どのような仕組みになっているのか分かりません。一部分であったり、簡単にでも大丈夫ですので、何が書かれているのか教えていただきたいです。コードが凄く長文ですいません。

### 該当のソースコード

```Kotlin

class LoginActivity : AppCompatActivity(), LoaderCallbacks<Cursor> {

    private var mAuthTask: UserLoginTask? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_login)
        // Set up the login form.
        populateAutoComplete()
        password.setOnEditorActionListener(TextView.OnEditorActionListener { _, id, _ ->
            if (id == EditorInfo.IME_ACTION_DONE || id == EditorInfo.IME_NULL) {
                attemptLogin()
                return@OnEditorActionListener true
            }
            false
        })

        email_sign_in_button.setOnClickListener { attemptLogin() }
    }

    private fun populateAutoComplete() {
        if (!mayRequestContacts()) {
            return
        }

        loaderManager.initLoader(0, null, this)
    }

    private fun mayRequestContacts(): Boolean {
        if (Build.VERSION.SDK_INT < Build.VERSION_CODES.M) {
            return true
        }
        if (checkSelfPermission(READ_CONTACTS) == PackageManager.PERMISSION_GRANTED) {
            return true
        }
        if (shouldShowRequestPermissionRationale(READ_CONTACTS)) {
            Snackbar.make(email, R.string.permission_rationale, Snackbar.LENGTH_INDEFINITE)
                .setAction(android.R.string.ok,
                    { requestPermissions(arrayOf(READ_CONTACTS), REQUEST_READ_CONTACTS) })
        } else {
            requestPermissions(arrayOf(READ_CONTACTS), REQUEST_READ_CONTACTS)
        }
        return false
    }

    override fun onRequestPermissionsResult(
        requestCode: Int, permissions: Array<String>,
        grantResults: IntArray
    ) {
        if (requestCode == REQUEST_READ_CONTACTS) {
            if (grantResults.size == 1 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                populateAutoComplete()
            }
        }
    }

    private fun attemptLogin() {
        if (mAuthTask != null) {
            return
        }

        // Reset errors.
        email.error = null
        password.error = null

        // Store values at the time of the login attempt.
        val emailStr = email.text.toString()
        val passwordStr = password.text.toString()

        var cancel = false
        var focusView: View? = null

        // Check for a valid password, if the user entered one.
        if (!TextUtils.isEmpty(passwordStr) && !isPasswordValid(passwordStr)) {
            password.error = getString(R.string.error_invalid_password)
            focusView = password
            cancel = true
        }

        // Check for a valid email address.
        if (TextUtils.isEmpty(emailStr)) {
            email.error = getString(R.string.error_field_required)
            focusView = email
            cancel = true
        } else if (!isEmailValid(emailStr)) {
            email.error = getString(R.string.error_invalid_email)
            focusView = email
            cancel = true
        }

        if (cancel) {
            // There was an error; don't attempt login and focus the first
            // form field with an error.
            focusView?.requestFocus()
        } else {
            // Show a progress spinner, and kick off a background task to
            // perform the user login attempt.
            showProgress(true)
            mAuthTask = UserLoginTask(emailStr, passwordStr)
            mAuthTask!!.execute(null as Void?)
        }
    }

    private fun isEmailValid(email: String): Boolean {
        //TODO: Replace this with your own logic
        return email.contains("@")
    }

    private fun isPasswordValid(password: String): Boolean {
        //TODO: Replace this with your own logic
        return password.length > 4
    }

    @TargetApi(Build.VERSION_CODES.HONEYCOMB_MR2)
    private fun showProgress(show: Boolean) {
        // On Honeycomb MR2 we have the ViewPropertyAnimator APIs, which allow
        // for very easy animations. If available, use these APIs to fade-in
        // the progress spinner.
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB_MR2) {
            val shortAnimTime = resources.getInteger(android.R.integer.config_shortAnimTime).toLong()

            login_form.visibility = if (show) View.GONE else View.VISIBLE
            login_form.animate()
                .setDuration(shortAnimTime)
                .alpha((if (show) 0 else 1).toFloat())
                .setListener(object : AnimatorListenerAdapter() {
                    override fun onAnimationEnd(animation: Animator) {
                        login_form.visibility = if (show) View.GONE else View.VISIBLE
                    }
                })

            login_progress.visibility = if (show) View.VISIBLE else View.GONE
            login_progress.animate()
                .setDuration(shortAnimTime)
                .alpha((if (show) 1 else 0).toFloat())
                .setListener(object : AnimatorListenerAdapter() {
                    override fun onAnimationEnd(animation: Animator) {
                        login_progress.visibility = if (show) View.VISIBLE else View.GONE
                    }
                })
        } else {
            // The ViewPropertyAnimator APIs are not available, so simply show
            // and hide the relevant UI components.
            login_progress.visibility = if (show) View.VISIBLE else View.GONE
            login_form.visibility = if (show) View.GONE else View.VISIBLE
        }
    }

    override fun onCreateLoader(i: Int, bundle: Bundle?): Loader<Cursor> {
        return CursorLoader(
            this,
            // Retrieve data rows for the device user's 'profile' contact.
            Uri.withAppendedPath(
                ContactsContract.Profile.CONTENT_URI,
                ContactsContract.Contacts.Data.CONTENT_DIRECTORY
            ), ProfileQuery.PROJECTION,

            // Select only email addresses.
            ContactsContract.Contacts.Data.MIMETYPE + " = ?", arrayOf(
                ContactsContract.CommonDataKinds.Email
                    .CONTENT_ITEM_TYPE
            ),

            // Show primary email addresses first. Note that there won't be
            // a primary email address if the user hasn't specified one.
            ContactsContract.Contacts.Data.IS_PRIMARY + " DESC"
        )
    }

    override fun onLoadFinished(cursorLoader: Loader<Cursor>, cursor: Cursor) {
        val emails = ArrayList<String>()
        cursor.moveToFirst()
        while (!cursor.isAfterLast) {
            emails.add(cursor.getString(ProfileQuery.ADDRESS))
            cursor.moveToNext()
        }

        addEmailsToAutoComplete(emails)
    }

    override fun onLoaderReset(cursorLoader: Loader<Cursor>) {

    }

    private fun addEmailsToAutoComplete(emailAddressCollection: List<String>) {
        //Create adapter to tell the AutoCompleteTextView what to show in its dropdown list.
        val adapter = ArrayAdapter(
            this@LoginActivity,
            android.R.layout.simple_dropdown_item_1line, emailAddressCollection
        )

        email.setAdapter(adapter)
    }

    object ProfileQuery {
        val PROJECTION = arrayOf(
            ContactsContract.CommonDataKinds.Email.ADDRESS,
            ContactsContract.CommonDataKinds.Email.IS_PRIMARY
        )
        val ADDRESS = 0
        val IS_PRIMARY = 1
    }

    inner class UserLoginTask internal constructor(private val mEmail: String, private val mPassword: String) :
        AsyncTask<Void, Void, Boolean>() {

        override fun doInBackground(vararg params: Void): Boolean? {
            // TODO: attempt authentication against a network service.

            try {
                // Simulate network access.
                Thread.sleep(2000)
            } catch (e: InterruptedException) {
                return false
            }

            return DUMMY_CREDENTIALS
                .map { it.split(":") }
                .firstOrNull { it[0] == mEmail }
                ?.let {
                    // Account exists, return true if the password matches.
                    it[1] == mPassword
                }
                ?: true
        }

        override fun onPostExecute(success: Boolean?) {
            mAuthTask = null
            showProgress(false)

            if (success!!) {
                finish()
            } else {
                password.error = getString(R.string.error_incorrect_password)
                password.requestFocus()
            }
        }

        override fun onCancelled() {
            mAuthTask = null
            showProgress(false)
        }
    }

    companion object {

        private val REQUEST_READ_CONTACTS = 0

        private val DUMMY_CREDENTIALS = arrayOf("foo@example.com:hello", "bar@example.com:world")
    }
}
```

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