通常，我们从某个数据源获取数据。
在我们的示例中，我们将创建虚假数据，这将是客户和员工的两个列表。
创建客户类
class Customer(var name: String, var job: String, var overDue: Float)创建员工类
class Employee(var nameEmployee: String, var jobEmployee: String)创建用于存储这两个列表的数据类
class Data(val customers: List<Customer>, val employees: List<Employee>)使用虚拟数据创建两个列表
val customers = ArrayList<Customer>() customers.add(Customer("Hala", "developer", 34.5f)) customers.add(Customer("Nora", "teacher", 43.5f)) customers.add(Customer("Rana", "doctor", 56.5f)) val employees = ArrayList<Employee>() employees.add(Employee("ALi", "carpenter")) employees.add(Employee("Yaser", "mechanic"))初始化 Gson 对象并使其全局化以便能够访问它
private var gson: Gson? = nullgson = GsonBuilder().serializeNulls().setPrettyPrinting().create()将类转换为 JSON 格式
private fun convertClassToJson(customers: List<Customer>, employees: List<Employee>): String? { val allData = Data(customers, employees) return gson?.toJson(allData)}添加写入和读取数据的权限
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" /><uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />检查是否已授予存储权限。
private fun isStoragePermissionGranted(): Boolean { return if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) { if (checkSelfPermission(Manifest.permission.WRITE_EXTERNAL_STORAGE) == PackageManager.PERMISSION_GRANTED) { //Permission is granted true } else { //Permission is revoked ActivityCompat.requestPermissions(this, arrayOf(Manifest.permission.WRITE_EXTERNAL_STORAGE), 1) false } } else { // Permission is automatically granted on sdk<23 upon installation true }}获取随机文件名，而不是覆盖相同的文件名
private fun getRandomFileName(): String { return Calendar.getInstance().timeInMillis.toString() + ".json"}将数据写入 JSON 文件
private fun writeTextToFile(jsonResponse: String?) { if (jsonResponse != "") { // Create a File object like this. val dir = File("//sdcard//Download//") val myExternalFile = File(dir, getRandomFileName()) // Create an object of FileOutputStream for writing data to myFile.txt var fos: FileOutputStream? = null try { // Instantiate the FileOutputStream object and pass myExternalFile in constructor fos = FileOutputStream(myExternalFile) // Write to the file fos.write(jsonResponse?.toByteArray()) // Close the stream fos.close() } catch (e: IOException) { e.printStackTrace() } Toast.makeText(this@MainActivity, "Information saved to SD card. $myExternalFile", Toast.LENGTH_SHORT).show() }}使用导出按钮备份数据
binding.btnExport.setOnClickListener { if (isStoragePermissionGranted()) { writeTextToFile(allJsonResponse) }}现在，您的数据将导出到手机下载文件夹中的JSON文件。
2. 从 JSON 文件导入数据
打开文件管理器以选择要导入的 JSON 文件
private fun openFileManager() { val intent = Intent(Intent.ACTION_OPEN_DOCUMENT) intent.addCategory(Intent.CATEGORY_OPENABLE) intent.type = "*/*" getDataFromFile.launch(intent)}从 JSON 文件中读取数据
private fun readTextFromUri(uri: Uri): String { var inputStream: InputStream? = null val stringBuilder = StringBuilder() try { inputStream = contentResolver.openInputStream(uri) val reader = BufferedReader(InputStreamReader(inputStream)) // Read a line of text. var line = reader.readLine() // Read the entire file while (line != null) { // Append the line read to StringBuilder object. Also, append a new-line stringBuilder.append(line).append('\n') // Again read the next line and store in variable line line = reader.readLine() } } catch (e: IOException) { e.printStackTrace() } return stringBuilder.toString()}在活动中获取 JSON 数据
private var getDataFromFile =registerForActivityResult(ActivityResultContracts.StartActivityForResult()) { result: ActivityResult -> if (result.resultCode == RESULT_OK) { val uri = result.data?.data val fileContents = readTextFromUri(uri!!) Toast.makeText(this@MainActivity, fileContents, Toast.LENGTH_SHORT).show() } }使用导入按钮恢复您的数据
binding.btnImport.setOnClickListener { openFileManager()}恭喜，您的数据是从 JSON 文件导入的，您现在可以将其插入到数据库中，或以适合应用程序用途的任何方式使用它。
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