Kotlin 파일처리 : 간단 일기장 앱 만들기

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      activity_main.xml
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<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:gravity="center"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <DatePicker
        android:datePickerMode="spinner"
        android:id="@+id/datePicker1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:calendarViewShown="false" />

    <EditText
        android:layout_weight="1"
        android:id="@+id/edtDiary"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="#00ff00"
        android:lines="8" >
    </EditText>

    <Button
        android:id="@+id/btnWrite"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:enabled="false"
        android:text="Button" />
</LinearLayout>

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    MainActivity.kt
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class MainActivity : AppCompatActivity() {
    lateinit var dp: DatePicker
    lateinit var edtDiary: EditText
    lateinit var btnWrite: Button
    lateinit var fileName: String

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        dp = findViewById<DatePicker>(R.id.datePicker1)
        edtDiary = findViewById<EditText>(R.id.edtDiary)
        btnWrite = findViewById<Button>(R.id.btnWrite)

        var cal = Calendar.getInstance()
        var cYear = cal.get(Calendar.YEAR)
        var cMonth = cal.get(Calendar.MONTH)
        var cDay = cal.get(Calendar.DAY_OF_MONTH)

        dp.init(cYear, cMonth, cDay) { view, year, monthOfYear, dayOfMonth ->
            fileName = (Integer.toString(year) + "_"
                    + Integer.toString(monthOfYear + 1) + "_"
                    + Integer.toString(dayOfMonth) + ".txt")
            var str = readDiary(fileName)
            edtDiary.setText(str)
            btnWrite.isEnabled = true
        }

        btnWrite.setOnClickListener {
            var outFs = openFileOutput(fileName, Context.MODE_PRIVATE)
            var str = edtDiary.text.toString()
            outFs.write(str.toByteArray())
            outFs.close()
            Toast.makeText(applicationContext, "$fileName 이 저장됨", Toast.LENGTH_SHORT).show()
        }
    }

    fun readDiary(fName: String) : String? {
        var diaryStr : String? = null
        var inFs : FileInputStream
        try {
            inFs = openFileInput(fName)
            var txt = ByteArray(500)
            inFs.read(txt)
            inFs.close()
            diaryStr = txt.toString(Charsets.UTF_8).trim()
            btnWrite.text = "수정 하기"
        } catch (e : IOException) {
            edtDiary.hint = "일기 없음"
            btnWrite.text = "새로 저장"
        }
        return diaryStr
    }
}