File Writer Compat


1.1.0 (Apr 11, 2023)
Apr 7, 2023
Apr 16, 2023
Akexorcist (akexorcist)
Akexorcist (akexorcist)
Source code


File Writer Compat

Android file writing helper library for API Level 21+



implementation 'com.akexorcist.filewritercompat:core:1.1.0'

// If you want to handle the runtime permission requesting from the library
implementation 'com.akexorcist.filewritercompat:permission:1.1.0'


  • Write files to these directories:
    • Internal app-specific file (/data/data/<package_name>/files/)
    • Internal app-specific cache (/data/data/<package_name>/cache/)
    • External app-specific file (/<external_storage>/Android/data/<package_name>/files/)
    • External app-specific cache (/<external_storage>/Android/data/<package_name>/cache/)
    • External shareable file (/<external_storage>/<directory_type>/)
  • Support for API level 21 - 33
  • Auto-create subdirectories
  • Built-in permission handling (additional dependency is required)
  • Auto media scanner triggers when saving a file in an external shareable directory


Common usage

suspend fun saveFileToInternalAppSpecificFile(
    activity: FragmentActivity,
    data: ByteArray,
    filename: String
) {
    val writer = FileWriterCompat.Builder.createInternalAppSpecificFile(
        fileNameWithExtension = filename,
        // (Optional) Auto-create sub directory if not exist
        // or skip this method to store the file in parent directory
    val result: FileResult<Uri, InternalAppSpecificFile.ErrorReason> = writer.write(activity, data)

All supported directories

// Internal app-specific file
val executor: InternalAppSpecificFile.Executor = FileWriterCompat.Builder
    .createInternalAppSpecificFile(/* ... */)
val result: FileRequest<Uri, InternalAppSpecificFile.ErrorReason> = executor.write(/* ... */)

// Internal app-specific cache
val executor: InternalAppSpecificCache.Executor = FileWriterCompat.Builder
    .createInternalAppSpecificCache(/* ... */)
val result: FileRequest<Uri, InternalAppSpecificCache.ErrorReason> = executor.write(/* ... */)

// External app-specific file
val executor: ExternalAppSpecificFile.Executor = FileWriterCompat.Builder
    .createExternalAppSpecificFile(/* ... */)
val result: FileRequest<Uri, ExternalAppSpecificFile.ErrorReason> = executor.write(/* ... */)

// External app-specific cache
val executor: ExternalAppSpecificCache.Executor = FileWriterCompat.Builder
    .createExternalAppSpecificCache(/* ... */)
val result: FileRequest<Uri, ExternalAppSpecificCache.ErrorReason> = executor.write(/* ... */)

// External shareable file
val executor: ExternalShareableFile.Executor = FileWriterCompat.Builder
    .createExternalShareableFile(/* ... */)
val result: FileRequest<Uri, ExternalShareableFile.ErrorReason> = executor.write(/* ... */)

Internal app-specific file's parameter


  • Filename with extension (String) - e.g, "image.jpg"


  • Child path (String) - e.g, "sample/exported"

Internal app-specific cache's parameter


  • Filename with extension (String) - e.g, "image.jpg"


  • Child path (String) - e.g, "sample/exported"

External app-specific file's parameter


  • Filename with extension (String) - e.g, "image.jpg"


  • Directory type (String) - e.g, Environment.DIRECTORY_PICTURES
  • Child path (String) - e.g, "sample/exported"

External app-specific cache's parameter


  • Filename with extension (String) - e.g, "image.jpg"


  • Child path (String) - e.g, "sample/exported"

External shareable file's parameter


  • Directory type (String) - e.g, Environment.DIRECTORY_PICTURES
  • Filename with extension (String) - e.g, "image.jpg"


  • Child path (String) - e.g, "sample/exported"
  • Storage permission request handing (StoragePermissionRequest) - e.g, NoOperationStoragePermissionRequest

Write external storage permission in external shareable file

The Manifest.permission.WRITE_EXTERNAL_STORAGE_PERMISSION must be granted when running on Android 10 or lower. No permission is required for Android 11 or higher.

There are two solutions to handle the runtime permission requesting in this library:

  1. Call the runtime permission requesting before calling this library when running on Android 10 or lower.
  2. Create a custom StoragePermissionRequest and inject it in ExternalShareableFile.Builder.
val customStoragePermissionRequest: StoragePermissionRequest = /* ... */
val executor: ExternalShareableFile.Executor = FileWriterCompat.Builder.createExternalShareableFile(/* ... */)

There are two built-in storage permission requests depending on what you want:

  • NoOperationStoragePermissionRequest - No operation, just check the permission.
  • PekoStoragePermissionRequest - Request the permission with Peko library
    • com.akexorcist.filewritercompat:permission:<latest_version is required.

You can customize this operation by your own:

object CustomStoragePermissionRequest: StoragePermissionRequest {
    override suspend fun requestWriteExternalStoragePermission(activity: FragmentActivity): Boolean {
        /* Any operation with boolean result */

Data type

There are 4 overloaded methods for the write method:

suspend fun write(activity: FragmentActivity, data: ByteArray): FileResult<Uri, ErrorReaon>
suspend fun write(activity: FragmentActivity, data: String): FileResult<Uri, ErrorReaon>
suspend fun write(activity: FragmentActivity, data: Any): FileResult<Uri, ErrorReaon>
suspend fun <DATA> write(activity: FragmentActivity, data: DATA, writer: (DATA, File) -> Unit): FileResult<Uri, ErrorReaon>

Additionally, you can create your custom data writer function for any data type.

For example:

val customWriter = { data: Int, file: File ->
  if (!file.exists()) {
  val fos = FileOutputStream(file)
  ObjectOutputStream(fos).use {

val data: Int = 1024
val activity: FragmentActivity
val executor: WriterExecutor<Uri, ErrorReason> = /* ... */
val result: FileResult<Uri, ErrorReason> = executor.write(activity, data, customWriter)

Error handling

When the write method is called, the result from this method will be FileResult<Uri, ErrorReason>.

The ErrorReason depends on what kind of directory you are using. For example, the result will be FileResult<Uri, ExternalShareableFile.ErrorReason> when you create the file writer with ExternalShareableFile.Builder.

val executor: ExternalShareableFile.Executor = /* ... */
val result: FileResult<Uri, ExternalShareableFile.ErrorReason> = executor.write(/* ... */)
when (result) {
    is FileResult.Success<Uri> -> {
        /* File was saved */
        val uri: Uri = result.result
    is FileResult.Error<ExternalShareableFile.ErrorReason> -> {
        /* File was not saved for some reason */
        when (result.reason) {
            is ExternalShareableFile.ErrorReason.WriteExternalStoragePermissionDenied -> {
                /* WRITER_EXTERNAL_STORAGE permission was denied */
            is ExternalShareableFile.ErrorReason.InvalidDirectoryType -> {
                /* Invalid directory type parameter */
            /* ... */

Each type of directory has a different error reason.


Minimum SDK version cannot be smaller than version 23 declared in library [com.markodevcic:peko:<version>]

This can happen when you use com.akexorcist.filewritercompat:permission, as the Peko library has a minimum SDK version at 23.

To solve this problem, declare the <uses-sdk> tag in your Android manifest to force usage:


  <uses-sdk tools:overrideLibrary="com.markodevcic.peko"/>

  <!-- ... -->


Copyright 2023 Akexorcist

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this work except in compliance with the License. You may obtain a copy of the License in the LICENSE file, or at:

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.