Question

I’m trying to export my application’s database to SDcard. It works excellent for emulator, bur not for my phone.

    OnClickListener mExportListener = new OnClickListener(){
public void onClick(View v){
    try {
        File sd = Environment.getExternalStorageDirectory();
        File data = Environment.getDataDirectory();
        if (sd.canWrite()) {
            String currentDBPath = "\\data\\com.mypck.myapp\\databases\\database";
            String backupDBPath = "database.db";
            File currentDB = new File(data, currentDBPath);
            File backupDB = new File(sd, backupDBPath);

            if (currentDB.exists()) {
                FileChannel src = new FileInputStream(currentDB).getChannel();
                FileChannel dst = new FileOutputStream(backupDB).getChannel();
                dst.transferFrom(src, 0, src.size());
                src.close();
                dst.close();
            }else{
             String msg = activity.getResources().getString(R.string.something_wrong);        
             Toast toast = Toast.makeText(getApplicationContext(), msg, Toast.LENGTH_LONG);  
             toast.show();
            }
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
}
};

This currentDB.exists() returns false on the phone, but I checked the file – it exists.
What is wrong with my phone?

Answer 1

You are supplying File wrong parameters. From Android doc:

File(String parent, String child) 
    parent - The parent pathname string
    child - The child pathname string 

In your code:

parent => \\data  
child => \\data\\com.mypck.myapp\\databases\\database  
resulting path => \\data\\data\\com.mypck.myapp\\databases\\database => wrong

It could be like this:

String sd = Environment.getExternalStorageDirectory();
if (sd.canWrite()) {
    String currentDBPath = "data/data/com.mypck.myapp/databases/your_database_name.db";
    String backupDBPath = sd + "/your_output_file_name.db";
    File currentDB = new File(currentDBPath);
    File backupDB = new File(backupDBPath);
    /* ... */

It surprises me this works on emulator, I doubt that. It probably creates an empty file becuase at least this line makes some sort of sense, although your variables are not what you named them:

File backupDB = new File(sd, backupDBPath);

Also you should probably create a finally block and do some FileChannel clean up in there.