Android：如何删除另一个包中的共享首选项

Question

In my android application I coded to read shared data of another Android application and then to delete that data from shared preferences. My code as follows :

try {

     con = createPackageContext("com.testapp.ws", 0);
     SharedPreferences pref = con.getSharedPreferences("demopref", Context.MODE_PRIVATE);
     ipAdr = pref.getString("demostring", "No Value");
     pref.edit().remove("demopref").commit();
   }

This shows following error:

06-12 11:52:07.400: E/ApplicationContext(3587): Couldn't rename file /data/data/com.testapp.ws/shared_prefs/demopref.xml to backup file /data/data/com.testapp.ws/shared_prefs/demopref.xml.bak

I used this method in my other application to make shared data

 public void shareData(){
    String strShareValue = ip;
    SharedPreferences prefs = getSharedPreferences("demopref",Context.MODE_WORLD_READABLE);
    SharedPreferences.Editor editor = prefs.edit();
    editor.putString("demostring", strShareValue);
    editor.commit();
}

How can I do that ? Is there anything to add Manifest file ?

Thanks!

Answer 1

If you use android:sharedUserId in your manifest files it should work. This is a permissions issue I've been running into myself.

To do this, you simply need to add a tag such as android:sharedUserId="com.example.you" to your <manifest> tag in your AndroidManifest.xml file for both of your applications (and the com.example.you has to be the same in both apps, of course).

Example start of the manifest file:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="package.name"
    android:versionCode="1"
    android:versionName="1.0"
    android:sharedUserId="com.example.you" >
...

For an indepth description of the way to get this working see my answer on How can I share a SharedPreferences file across two different android apps?

Answer 2

You need to use MODE_WORLD_READABLE instead of MODE_PRIVATE . Read the docs for further information.

Here's a tutorial to check further if you have any more mistakes.

Answer 3

While the other solutions here will technically work in most circumstances, the framework that Android has provided to you for sharing data between processes/applications is the ContentProvider . It may seem like a lot of extra abstraction, but it's the one that is guaranteed to work.

While the interface for this component mirrors the calls into a database, the underlying data structure can be anything you like. In specific, you can return a MatrixCursor in response to queries that provides the contents of your SharedPreferences object, and you can implement a URI scheme for delete/update calls that can be used to modify the preferences from other applications.

Here is a link to a blog post from another developer who used MatrixCursor to share preferences.

HTH

Answer 4

I've been struggling with SharedPreferences the last three days, but I think I finally solved it for myself. Here's a few tips and gotchas you should try out that might help you (and loads of other stackoverflow users).

Please note that all my observations are for ICS (4.0.2 and 4.0.4).

1. If you change the android:sharedUserId , delete the app as file/folder permissions will be incorrect. So you shouldn't change that value if you have already relased the app.
2. If you change the Context.MODE_* values, delete the app's data (or the whole app) to ensure file permissions aren't incorrect.
3. If you use android:sharedUserId , be sure to sign the apps with the same certificate .
4. Use a different filename for the preferences in the two apps. I had problems with the app just reading the local shared preferences even though I used createPackageContex() .

This is what worked for me in the end:

1. I used the same android:sharedUserId for the two apps. (Not the same android:process .)
2. I used Context.MODE_WORLD_READABLE for both reading and writing local prefs, and for reading the other app's prefs.
3. I used Context.CONTEXT_IGNORE_SECURITY when calling createPackageContext() .