Native file documents

Category: Modules
Subcategory: Messaging


View file documents on the device. Access the file system of the native device. Share documents to other apps on the device. Resize and crop images. Use a text file on the device as log.


Demo url


Access the file system of the native device. View file documents on the device, as temporary solution until the Mendix platform supports this.

Due to the nature of this module, it comes with a disclaimer and warning, by using this module you accept and agree to it:

This module provides a convenient way for viewing files and images. However, it is an advanced, highly technical module! You need to create a custom build to use it, it does not work in the Make It Native app!

The module is free to use, as is, and we will update it regularly for new Mendix releases.

Unfortunately, we cannot provide extended support on using this module. The functions are documented and a sample project will be available too.

Be advised that incorrect usage of the JavaScript actions in this module can cause issues in your app, like deleting files that you did not create yourself. We do not accept any liability or responsibility!

If you are interested we are of course willing to provide assistance, you may contact use here:


Since you’re still reading, now comes the good stuff!

Typical usage scenario

To work with file documents on the native device

Features and limitations

JavaScript actions:

  • copyFile
  • cropImage
  • cropImageCleanupTempFiles
  • deleteItem
  • downloadFile
  • exists
  • getFileDocumentUrl
  • getFullPath
  • getPlatform
  • IsNativeFileSystemAvailable
  • mkdir
  • moveFile (also can rename files)
  • openDocumentPicker
  • readDir
  • readFile
  • resizeImage
  • saveToMendixFileDocument
  • shareOpen
  • stopDownload
  • viewFile
  • writeFile
  • writeTextFile

Each action is documented in the module. Most have a writeToLog parameter, which controls whether the log details are written to NativeActionLog. Snippet Snippet_SyncDebug_NativeActionLog shows the log on the native app.

Just make sure to call IsNativeFileSystemAvailable at least once in your app. This is good practice anyway, it also allows your app to fail gracefully when a developer attempts to use the functionality in the Make It Native app.


  • PDF viewer

Viewing file documents and images

It is possible to synchronize FileDocument entity types to the device. However, currently the viewFile JS action does not work with them because the file on the device has lost the file extension. The extension is necessary for the library to work correctly.

To come around this issue, nanoflow SUB_ViewDocument is available. It can be called with any specialization of FileDocument and will copy the file on the device to its original name and start the viewer.

Supported file types are PDF, JPG, PNG. Most Office types are supported too but on Android these open in the specific app.

Unsupported file types are treated differently on each platform: On Android nothing will happen at all on older versions, but recent Android versions throw an error when file cannot be viewed. On iOS, the viewer will open but not show any contents.

Viewing PDF documents

On Android the PDF will be opened in a separate app when using the viewFile JS action. The PDF Viewer widget allows PDFs to be viewed without leaving the Mendix app. The only property is the path to the file. The same restrictions apply as with viewing other documents: the extension must be correct. On top of that, the path must be specified differently for iOS and Android.

To make viewing PDFs easy, nanoflow SUB_CopyPdfForViewing is available. Similar to SUB_ViewDocument, it will copy the file on the device to its original name. However, the PDF viewer is a widget so the nanoflow will return the path to the file as result. 

Create your own page context object and store the path in an unlimited string attribute. Configure that attribute on the widget property and it will work.

Again, make sure to cleanup the viewer temp files often!

Reading contents of a file

For some libraries, the contents of the file need to be passed in base64 encoded format. The readFile JS action does just that.

For ease of use, two nanoflows are provided:

  • SUB_ReadFileBase64: Reads content from the passed FileDocument directly.
  • SUB_ReadFileBase64WithCopy: First copies the file to a temp file, similar to viewing documents.

When using the readFile JS action in real life situations, it turned out that copying the file before reading its contents is not required.

So it is expected SUB_ReadFileBase64 can be used in all situations. As fallback, SUB_ReadFileBase64WithCopy is provided as well.

Temp files cleanup

 The viewFile action cannot tell if and when the viewer was closed. So there will be temporary copies on the device. Nanoflow SUB_DeleteFileViewerTempDirectory deletes the temporary stuff so be sure to call that flow regularly. This also applies when using the PDF Viewer widget and resizing images.

Document picking on the device

With JavaScript action openDocumentPicker the user can select documents to be used in the Mendix app. The result has a uri, which can be saved into a Mendix FileDocument using JavaScript action saveToMendixFileDocument. The sample project has an  example of this.

Resizing images

Quite often images need to be small for sharing and larger to store full details on the server. Of course the image size can be limited while taking a picture but what if you want a hires picture and share a smaller sized one? The JS action resizeImage can be used to resize an image. It requires a path to a file on the device so the Mendix Image object must first be prepared using nanoflow SUB_CopyMendixFileDocumentForViewing. The returned path can be used to resize the image to a new file. The JS action returns an object with the new image dimensions, the file name and the file path. You can use the file path as parameter for JS action saveToMendixFileDocument to store the resized image in a Mendix Image object. Again, this creates temporary files in the app storage so be sure to clear the temp directory. The parameters are described in detail on the JS action itself. The demo app has an example on taking a hires picture and resizing it.

Cropping images

While taking a picture, the image can be cropped on the camera. The JS action cropImage allows you to crop an image stored earlier as Mendix Image object. Note that this action too requires a path to a file so the Mendix Image object must first be prepared using nanoflow SUB_CopyMendixFileDocumentForViewing. The returned path can be used as input for cropImage. This JS action starts a UI where the user can drag and pinch-zoom to adjust the content. Upon completion, a Mendix object is returned which contains a full path to the result image. This image can be stored into a new Mendix image object using saveToMendixFileDocument. Be sure to delete the file yourself as the crop library does not know when we're done with it. The result size you specify also defines the aspect ration of the crop frame shown to the user. Note that the result width/height may be larger than the screen size of the device. The frame is scaled to the screen using the dimensions you specify. There is also a cleanup JS action, cropImageCleanupTempFiles, The crop library can use temporary files, calling the cleanup JS action makes sure these are deleted as well. The demo app has a sample of cropping an image and saving the result in a new image.

Sharing content

With JavaScript action shareOpen the user can share content outside the app. Note that the share JavaScript action in NanoflowCommons allows you to share single texts, so if that is your requirement, no need for anything more. With shareOpen, you can share documents as well. The sample project has an  example of this.

Limitation: Some apps handle the content passed to them better than others. For example, the iOS default mail app will accept subject, body message and one or more images or documents in one shareOpen call. WhatsApp on iOS will ignore any documents as soon as texts are passed as well. Currently the only way around this is to share any images or documents in a separate shareOpen call. Be sure to test on both platforms to check whether the result matches the requirements of your app!

Writing to a text file and use it as a simple log file

Resolving production issues can be quite difficult, especially intermittent issues. There are logging frameworks but mostly they will store the logdata on the cloud. For some organizations that can conflict with security policies as detailed logging can contain sensitive data.

For this situation, a simple logging has been added that uses text files on the device to record the logging. These files are kept in the app container itself. In the example, the logfiles can be viewed on the device and shared to other apps. Of course it is also possible to store the logfile as Mendix FileDocument.

Please note this is not a full-fledged logging framework, use it if policies prohibit the use of cloud frameworks. 

JavaScript action writeTextFile is used to write the data to a file.

To make logging easier, several nanoflows are available in the Nanoflows file logger, to initialize a logfile and log data to it. A cleanup function is also available, which can be called when opening the app or at any other suitable point in your process. The default implementation creates a new logfile everyday. If desired there is a function to start a new log file for the same day.

These nanoflows can be used as is or serve as an example to create your own logging implementation.

The sample project has a fully working example of all features.



Download the Mendix appstore module.

Make sure that the NativeActionLog synchronization setting is set to 'Nothing’. (Native navigation profile, Sync configuration button)

Custom logic to turn logging on or off

Previously, an attribute on Administration.Account was used to turn logging on or off. This caused issues in apps where a specialization of Account is used. So the native part of the module does not retrieve Account anymore. Account is used as parameter in several places, allowing a specialization to be used as well.

To control logging, nanoflow SUB_IsLoggingEnabled calls nanoflow Application.SUB_NativeFileDocuments_IsLoggingEnabled and expects a boolean return value. In the demo app, this nanoflow just retrieves the Account for the current user and returns Account/OfflineDebug. (See screenshot.)

After installing or upgrading the module, you will get an error because most probably you don't have that nanoflow.


  • Create nanoflow Application.SUB_NativeFileDocuments_IsLoggingEnabled and make it return a boolean value. Retrieve Account for the current user and return Account/OfflineDebug to keep things the same as they were before the upgrade. Retrieve your own specialization of Account if applicable.
  • Create a nanoflow with any name that suits you and make that return a boolean value. Change nanoflow SUB_IsLoggingEnabled to call your nanoflow. Everytime you update NativeFileDocuments you will need to make that change again. (Hopefully in the future this change will stick.)
  • Change nanoflow SUB_IsLoggingEnabled to include your logic to determine a boolean value that controls logging. Least desirable option as your logic will be gone after upgrading the module. Best to use a nanoflow call for that purpose.

Native build

Create a native build using the native builder UI. You need at least version 1.0.78 and allow it to update the native template if it prompts you for the update. The additional native module dependencies will be included automatically during the native build for Mx9.

When building for Mx8, use npm install to include the native dependencies react-native-fs, react-native-file-viewer, react-native-share and react-native-document-picker. Check the native dependency files in javascriptsource\nativefiledocuments\actions\ for the right version!

Also run pod install in the ios folder again for iOS builds.

Android specific

You need to add a query to the Android Manifest for Android 11 and up. Place it directly before the close tag, see screenshot. Note that recent versions of the native template add a similar intent by default so you no longer need to do this manually.


Version: 4.1.0
Framework Version: 9.12.2
Release Notes: Added image crop action
Version: 4.0.0
Framework Version: 9.12.1
Release Notes: *** Breaking change *** Write to log flag is no longer determined directly from Account. In apps where a specialization of Account is used this caused issues in the native app. After upgrading you will see an error that nanoflow Application.SUB_NativeFileDocuments_IsLoggingEnabled does not exist. See documentation for details. Marked JS actions as native only.
Version: 3.3.0
Framework Version: 9.6.5
Release Notes: Write to text files. Use a text file as basic logfile.
Version: 3.2.1
Framework Version: 9.6.5
Release Notes: Optimizatin for using readFile JS action. See documentation.
Version: 3.2.0
Framework Version: 9.6.5
Release Notes: You need to build your native app again because native dependencies have been added - Added PDF viewer widget to view PDFs without leaving the app. - Added nanoflow SUB_CopyPdfForViewing to allow easy use of the PDF viewer widget easier. - Added getPlatform JS action - Added resizeImage JS action - Added readFile JS action and nanoflow SUB_ReadFileBase64 - Fixed JS action exception handling