Writing to and reading from text files in App Inventor programs

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15 Responses

  1. Roberto says:

    I need some help. I used the exact code above in a program running on an Xperia Z2, but neither the append to file neither the save file where able to actually create a file in the phone memory. I really can’t find out what’s going wrong. Do you have any suggestions?

    • Edward M says:

      My guess:
      1. The file is in the phone’s memory but in a different location than expected. I downloaded an app named “File Manager” (there are several like this) from the Google Play store and use that to look at the folders/files on the phone. I suspect you have already done that. Or mount the phone’s file storage as a hard drive, by connecting to a PC with a USB cable, which you probably already tried too.
      2. Or the App Inventor functionality has changed. I will be looking at file operations again soon and will see if they have made changes. There have been some updates recently, such as use of the new AI Companion.


  2. Colin Walsh says:

    Hi Ed,
    Sorry to bother you over the holidays but, the same thing is happening to me as Roberto.
    While connected to MIT AI2 wirelessly the File component works fine it saves my data to “/AppInventor/data/filename.txt” and I can read it no problem, but If I package the app to an .apk nothing happens, no file saved, no error message, nothing.
    I’ve used ES file explorer and can’t find any files with names I’ve used.
    If I type in the path “/AppInventor/data/myfilename.txt” into the packaged app it works, so maybe its a problem with the path?
    I hope you can help and anyway have a nice one Ed.

    • Edward M says:

      Hi Colin,
      I am out this weekend but i will look at that on Tuesday of the coming week. Your findings on this are interesting and suggest there is something not implemented properly by Appinventor as the code, obviously, should work the same in AI2 Companion or as a compiled .apk file.

      If file i/o does not work in the .apk file, there may be a work around. There used to be a code library in the Google Play store that can be used by Appinventor programs. This code library supports file read/write, and is accessed through the Start Activity block component. I suspect the library is still available – I just need to find it! One way or another, I think we can find a solution so this works!

      More in the next few days!


      • Edward M says:

        Some progress!

        IF the phone has an actual micro SD card installed, and IF the file name is prefaced with a forward slash “/”, then the file is created on the SD card in its root directly.

        Example filename:

        This works the same way in both AI2 Companion and as a built .apk file.

        If you change the filename to
        It is created and stored on the sdcard in the /download folder.

        I have also gotten this to work on the Nexus 5 and now know where the file is. Not yet sure how to copy it back to a Windows PC, though.

        Much progress has been made. I’ll be making a new blog post once I get this all sorted out! We will get this working for you!


    • Edward M says:

      Colin and Roberto,
      I do not yet have this solved – however, it appears the file has been created and retained on the phone – but where?

      I made a small app to create a file and write one line of text to the file. I ran one version using AI2 Companion and looked at the phone’s file using a File Manager app (on the phone). The file I created “testfile2.txt” was located inside the Appinventor/data directory. However, when I look at this phone’s file directory when plugging the phone over USB into a computer, the file “textfile2.txt” is not visible in the directory!

      I plugged the phone in to Windows – and the file is not there. I plugged into Mac OS X and used Android File Transfer to look at the Android file system on the phone and “textfile2.txt” is not visible there either.

      I went back to the File Manager app on the phone and it still sees the file.

      I created a separate test app and built it as an .apk file, installed that, and had the same result. This version creates a “textfile3.txt” file. I can run my test app and read the textfile3.txt into my program just fine, meaning it must exist somewhere.

      What I think is happening is that Android works with more than one kind of file system. Parts of the file structure are “partitioned” using a Windows FAT32 compatible file system – and this is visible when the device is plugged into to Windows or into Mac OS X (with the write software installed on Mac OS X). However, Android also uses a Linux-based filed system called EXT4 and this is, I think, not visible to Windows or Mac OS X.

      I think I can get an EXT4 driver for either my Windows or Mac computers and will check this out further.


    • Edward M says:

      Some additional info – I tried to run the AI2 companion version of my file i/o app on an old Android 2.2 phone that has an SD card slot – but no micro SD card installed.

      When I run the test code, it gives an error that it cannot access /mnt/sdcard/AppInventor/data/textfile2.txt – which is correct because on that phone, the SD card is not installed.

      I can not run the .apk version since all downloads go to the sdcard. I do have a spare micro SD card somewhere around. I have a hunch if I install that, this might actually run and the file may be hidden on it.

      I vaguely think that Android 2.2 may have used the FAT32 file system and did not have the EXT2, 3 or 4 file systems.

  3. Tobias says:

    Thanks for the tutorial.
    I want to fill the file the whole text of a website. Is this possible?

    • Edward M says:

      Do you mean you want to copy a remote web site text to the phone? Or you want to create a bunch of html text files on your phone?


  4. please help! can i save files on dropbox ?
    i need a way to let my app to read text file from dropbox

    • Edward M says:

      Am trying to think of a way to solve this … App Inventor itself cannot do a lot with Dropbox but there may be some ways to work with this.

      1. On Windows and Mac OS X, the Dropbox file transfer program runs in the background. As new files are added to the Dropbox, they are synchronized to and from the Dropbox server and your computer. I do not know if the Android Dropbox app works this way, but if it does, it may be possible to read and write files in the Android folder that holds the Dropbox file.

      2. There is way using the Sharing component (See Social | Sharing in the Palette) to hand a file to another “Sharing” app. The way this works is that Android apps register something called and “intent” – meaning a list of functions that they can provide other applications. Let’s say we have an app that would like to send an EMAIL message. You can use the Sharing component. This leads to Android displaying a list of applications that can “Share” items (Gmail is one of them, in this case). You select GMail (And even make it the default for future sharing) and you can pass to it a piece of text or an entire file. What I am thinking is that Sharing might also bring up the Android Dropbox app and you might be able to send a file to Dropbox for uploading to Dropbox. This does not solve the problem with getting or reading a file from Dropbox, but is a possible idea for the other direction.

      I will add this to my list of items to experiment with and see if I might come up with something later.


  1. May 2, 2015

    […] post is a major update to a previous post on reading and writing text files using App Inventor. This revision includes information on how to locate the text files you create in your App Inventor […]

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