覆盖我的应用程序中的文件

Question

When I start the application I will invoke a web service and save a file returned by the service in my app. For offline purposes i want to have a file in my app, in case the web service is down.

My question is: I want to overwrite the file i have, with the file I received from the web service. How should i do this? Where should i save the files to be able to perform this task?

I was saving the file received in my internal storage, but the offline file I don´t know where i should save it. Any code? Indications? New to this.

Answer 1

I would suggest:

• Keep your file inside of your project (APK)
• On first start, copy this file to local storage
• On successful web API return, copy (and overwrite) the file on local storage.
• Always read from the file on local storage

You should save files in your application's internal storage directory by using getExternalStorageDirectory which will put your files in this location: /Android/data/<package_name>/files/ . This is the best location to put files because when your application is uninstalled, the files in this directory will also be removed.

More info see: http://developer.android.com/guide/topics/data/data-storage.html#filesExternal and http://developer.android.com/training/basics/data-storage/files.html

Answer 2

There are basically two locations in android you can use to save files. The external storage accessible to the user and all the applications, or the private directory dedicated to your app. For your purpose the later seems more appropriate.

For manipulating files in your private storage see the openFileInput and openFileOutput (and other) methods in the Context class.

Save example:

FileOutputStream fos = context.openFileOutput("my-file", Context.MODE_PRIVATE);
fos.write(bytes);
fos.close();

Load example:

File f = new File(context.getFilesDir(),"my-file");
if (f.exists()) {
    byte[] bytes = new byte[(int)f.length()];
    FileInputStream fis = context.openFileInput(f.getName());
    fis.read(bytes);
    fis.close();
}