How do I take advantage of Android's "Clear Cache" button

Question

In Android's settings, in the "Manage Applications" activity when clicking on an app, the data is broken down into Application, Data, and cache. There is also a button to clear the cache. My app caches audio files and I would like the user to be able to clear the cache using this button. How do I store them so they get lumped in with the cache and the user can clear them? I've tried storing files using both of the following techniques:

newFile = File.createTempFile("mcb", ".mp3", context.getCacheDir());


newFile = new File(context.getCacheDir(), "mcb.mp3");
newFile.createNewFile();

In both cases, these files are listed as Data and not Cache.

Answer 1

I can't reproduce your problem, perhaps something else is wrong.

Using the following application, I was able to create a file in the cache directory and then clear it using the Manage Applications function under Settings. I didn't have to change anything in the manifest and from what I can tell, you really shouldn't mess with the android:allowClearUserData option.

public class CreateCacheFile extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        Button button = (Button) findViewById(R.id.CreateFileButton);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                File file = new File(
                        CreateCacheFile.this.getCacheDir(), "temp.txt");

                try {
                    file.createNewFile();
                    FileWriter fw = new FileWriter(file);
                    BufferedWriter bw = new BufferedWriter(fw);
                    bw.write("Hello World");
                    bw.newLine();
                    bw.close();

                } catch (IOException e) {
                    Toast.makeText(
                            CreateCacheFile.this, 
                            "Error!", 
                            Toast.LENGTH_SHORT).show();
                }
            }
        });
    }
}

After running the application (and clicking the button to create the file):

$ adb -d shell
# ls /data/data/com.example.CreateCacheFile/cache
temp.txt
# cat /data/data/com.example.CreateCacheFile/cache/temp.txt
Hello World
# 

Manage Applications reports that 4KB of space is in use for Cache. After clicking the button to clear it:

# ls /data/data/com.example.CreateCacheFile/cache
# cat /data/data/com.example.CreateCacheFile/cache/temp.txt
temp.txt: No such file or directory
# 

At this point Manage Applications reports that 0KB of space is in use for Cache.

Answer 2

I think you have to make use of android:allowClearUserData and android:manageSpaceActivity under your <application> tag to see that option in 'Manage Applications'. See http://developer.android.com/guide/topics/manifest/application-element.html for more information.

Alternatively, have an option for clearing cache in your activity.