Android保存PDF到外部存储遇EPERM权限错误，求解决

尝试将PDF文件保存到外部存储时，出现以下错误：

Caused by: android.system.ErrnoException: open failed: EPERM (Operation not permitted)

1) 权限检查逻辑 #

应用启动时会执行存储权限检查：

private fun initAndCheckPermissions() {
    bmp = BitmapFactory.decodeResource(resources, R.drawable.logo_nuin_nomb_subt)
    scaledbmp = Bitmap.createScaledBitmap(bmp, 140, 140, false)
    if (checkPermissions()) {
        // 权限授予后提示
        Toast.makeText(requireContext(), "Permissions Granted..", Toast.LENGTH_SHORT).show()
    } else {
        requestPermission()
    }
}

fun requestPermission() {
    ActivityCompat.requestPermissions(
        requireActivity(),
        arrayOf(
            Manifest.permission.READ_EXTERNAL_STORAGE,
            Manifest.permission.WRITE_EXTERNAL_STORAGE
        ), PERMISSION_CODE
    )
}

override fun onRequestPermissionsResult(
    requestCode: Int,
    permissions: Array<out String>,
    grantResults: IntArray
) {
    super.onRequestPermissionsResult(requestCode, permissions, grantResults)
    if (requestCode == PERMISSION_CODE) {
        if (grantResults.size > 0) {
            if (grantResults[0] == PackageManager.PERMISSION_GRANTED && grantResults[1]
                == PackageManager.PERMISSION_GRANTED) {
                Toast.makeText(requireContext(), "Permission Granted..", Toast.LENGTH_SHORT).show()
            } else {
                requireActivity().finish()
            }
        }
    }
}

PDF生成逻辑 #

用户点击按钮时，生成包含文本和图片的PDF文件：

@RequiresApi(Build.VERSION_CODES.KITKAT)
fun generatePDF() {
    var pdfDocument: PdfDocument = PdfDocument()
    var paint: Paint = Paint()
    var title: Paint = Paint()
    var myPageInfo: PdfDocument.PageInfo? =
        PdfDocument.PageInfo.Builder(pageWidth, pageHeight, 1).create()
    var myPage: PdfDocument.Page = pdfDocument.startPage(myPageInfo)
    var canvas: Canvas = myPage.canvas
    canvas.drawBitmap(scaledbmp, 56F, 40F, paint)
    title.typeface = Typeface.create(Typeface.DEFAULT, Typeface.NORMAL)
    title.textSize = 15F
    title.color = ContextCompat.getColor(requireContext(), R.color.purple_200)
    canvas.drawText("A portal for IT professionals.", 209F, 100F, title)
    canvas.drawText("Geeks for Geeks", 209F, 80F, title)
    title.typeface = Typeface.defaultFromStyle(Typeface.NORMAL)
    title.color = ContextCompat.getColor(requireContext(), R.color.purple_200)
    title.textSize = 15F
    title.textAlign = Paint.Align.CENTER
    canvas.drawText("This is sample document which we have created", 396F, 560F, title)
    pdfDocument.finishPage(myPage)
    val file: File = File(Environment.getExternalStorageState(), "GFG.pdf")
    pdfDocument.writeTo(FileOutputStream(file))
    Toast.makeText(requireContext(), "PDF file generated..", Toast.LENGTH_SHORT).show()
    pdfDocument.close()
}

核心问题 #

错误触发自以下代码行：

val file: File = File(Environment.getExternalStorageState(), "GFG.pdf")

对应的错误信息：

Caused by: android.system.ErrnoException: open failed: EPERM (Operation not permitted)

解决方案 #

1. 修复路径参数错误

Environment.getExternalStorageState()返回的是存储状态字符串（如mounted），并非存储目录路径。需替换为正确的目录获取方法：

• Android 9及以下：使用Environment.getExternalStorageDirectory()
• Android 10+：受Scoped Storage限制，需按以下方案调整

2. 适配Android 10+存储策略

方案A：使用应用专属外部存储（无需额外权限）

此目录下的文件仅当前应用可访问，卸载应用时会被自动删除，无需申请存储权限：

// 获取应用专属文档目录
val dir = requireContext().getExternalFilesDir(Environment.DIRECTORY_DOCUMENTS)
val file = File(dir, "GFG.pdf")

方案B：保存到公共目录（需权限适配）

若必须保存到公共目录：

• Android 10-12：在AndroidManifest.xml的<application>标签中添加android:requestLegacyExternalStorage="true"，兼容旧存储模式
• Android 13+：申请READ_MEDIA_*系列权限，写入公共目录需使用MediaStore API；或申请MANAGE_EXTERNAL_STORAGE权限（需通过Google Play审核）

3. 权限逻辑优化

Android 10+版本中，即使申请了WRITE_EXTERNAL_STORAGE权限，在Scoped Storage模式下也无法直接写入公共目录，需按上述方案调整存储路径或权限策略。

内容的提问来源于stack exchange，提问作者Janzek