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Totally confused. Trying to save / load files in Android

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  1. edzillion

    edzillion New Member This Topic's Starter

    Nov 11, 2009
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    I have read through numerous tutorials, which all tell me a little bit but I am lost on the overall picture. So how about I start at the start.

    I have a Java app I wrote that saves a string of data as a csv file: data.txt - I want to be able to open this file in my android app, so the first thing I did was use the 'push' option in eclipse to save it onto the device. i could save it and view it on the sdcard, but when trying to dave to the app data folder (data/data/package) it seems to work but I cannot see the file there.

    So after reading around I saw this piece of code:

    Code (Text):
    1.         try { // catches IOException below
    2.             final String TESTSTRING = new String("Hello Android");
    4.             // ##### Write a file to the disk #####
    5.             /* We have to use the openFileOutput()-method
    6.             * the ActivityContext provides, to
    7.             * protect your file from others and
    8.             * This is done for security-reasons.
    9.             * We chose MODE_WORLD_READABLE, because
    10.             * we have nothing to hide in our file */
    11.             FileOutputStream fOut = openFileOutput("samplefile.txt",
    12.             MODE_WORLD_READABLE);
    13.             OutputStreamWriter osw = new OutputStreamWriter(fOut);
    15.             // Write the string to the file
    16.             osw.write(TESTSTRING);
    17.             /* ensure that everything is
    18.             * really written out and close */
    19.             osw.flush();
    20.             osw.close();
    21.             // ##### Read the file back in #####
    23.             /* We have to use the openFileInput()-method
    24.             * the ActivityContext provides.
    25.             * Again for security reasons with
    26.             * openFileInput(...) */
    27.             FileInputStream fIn = openFileInput("samplefile.txt");
    28.             InputStreamReader isr = new InputStreamReader(fIn);
    29.             /* Prepare a char-Array that will
    30.             * hold the chars we read back in. */
    31.             char[] inputBuffer = new char[TESTSTRING.length()];
    32.             // Fill the Buffer with data from the file
    33.             isr.read(inputBuffer);
    34.             // Transform the chars to a String
    35.             String readString = new String(inputBuffer);
    37.             // Check if we read back the same chars that we had written out
    38.             boolean isTheSame = TESTSTRING.equals(readString);
    40.             // WOHOO lets Celebrate =)
    41.             Log.i("File Reading stuff", "success = " + isTheSame);
    43.         } catch (IOException ioe) {
    44.             ioe.printStackTrace();
    45.         }
    46.     }
    which works fine, though I cannot seem to see the file (I presume this is because it is located in the data/data/package/ folder and I cannot see that through eclipse DDMS.

    >> Aside: I seem to have a lot of trouble accessing the file explorer using eclipse. It seems v. tempermental - sometimes I can see all the files and folders, other times I cannot open any of the folders (though it does list data, sdcard and system), with no discernable reason. I just did a test: loaded up the emulator on its own with wipe data set to 'on' and I can access the data folder but no subfolders of it :mad:

    Anyway, When I try to use this same code to read my data.txt file from the sdcard I get the error: File sdcard/data.txt contains a path separator (I also tried the path /sdcard/data.txt but got the same error.

    I read somewhere that openFileInput will not work with the sdcard.

    This is really a kind of kludge just to test the data, since in the finished product the app wont read data from the sdcard. Am I missing something, should I serialise the data as XML? What is the best practice here?


  2. galt

    galt Well-Known Member

    Oct 26, 2009
    Likes Received:
    If your final app will not need to read the card, why not just create your data in a resource file as a string or array, or whatever form best matches the ultimate data source ?
  3. edzillion

    edzillion New Member This Topic's Starter

    Nov 11, 2009
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    Good point. I guess I was getting tunnel vision there;

    What if, say, an application had episodic content? How would the app be updated? Can a server push an update other than the usual android market updates, or would the user have to initiate an update from a webserver or something ...
  4. khooke

    khooke Member

    Aug 31, 2009
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    your app could call a remote web service on your server on startup or some other timed basis to check for available downloadable new content?
  5. eialbur

    eialbur New Member

    Mar 29, 2011
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    I need an answer as well - in fact I am running into a number of developers in this situation.

    I do not want to package my 'data' files as a Resource - I want them out on the file system (and I don't want copies of the data files left as a Resource). I want to be able to update and add to the data files without having to reinstall the app.

    For example - Mahjongg on Linux. You can change the tile set (or add to the tile sets) just by dropping a specially formated file into a specific directory. I want to do something like that. I want to have different data files the user can choose to 'install' into this directory (different data files should be different items in the Marketplace).

    I have found a number of other developers wanting this capability, but I haven't seen any solutions yet. I'm new to Android ... can some give me an answer (or point me in the right direction) ?

    P.S. I do not want to set up my own server and write my own data download code.
  6. alostpacket

    alostpacket Over Macho Grande? VIP Member

    Nov 29, 2009
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    Lots of apps do this actually...

    You could maybe start here:

    PackageManager | Android Developers

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