<EditText
    android:id="@+id/editText"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:hint="Please write something here"
    />

override fun onDestroy() {
    super.onDestroy()
    val inputText = editText.text.toString()
    save(inputText)
}

private fun save(inputText : String) {
    try {
        val output = openFileOutput("data", Context.MODE_PRIVATE)
        val write = BufferedWriter(OutputStreamWriter(output))
        write.use {
            it.write(inputText)
        }
    } catch (e : IOException) {
        e.printStackTrace()
    }
}

//取出文件中所保存内容
private fun load() : String {
    //把文件取出的数据一行行拼接在StringBuilder对象当中，用于返回内容（String）
    val content = StringBuilder()
    try {
        //获取FileInputStream对象
        val input = openFileInput("data")
        //构建BufferedReader对象
        val reader = BufferedReader(InputStreamReader(input))
        //读取文件内容
        reader.use {
            //Kotlin提供的一个内置扩展函数，可以将读到的每行内容都回调到Lambda表达式中，然后在Lambda表达式中完成拼接逻辑
            reader.forEachLine {
                content.append(it)
            }
        }
    } catch (e: IOException) {
        e.printStackTrace()
    }
    return content.toString()
}

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)
    val inputText = load()
    //数据不为空则将内容填充到EditText中
    if (inputText.isNotEmpty()) {
        editText.setText(inputText)
        //光标（焦点）位置移到文字末
        editText.setSelection(inputText.length)
        //还原成功提示
        Toast.makeText(this, "Restoring succeeded", Toast.LENGTH_SHORT).show()
    }
}