Android Tutorial - Chapter 5 Saving Data

P1_KeyValue.java

// use SharedPreferences APIs for small collection of data

// 1. using key
SharedPreferences pref = anyContext.getSharedPreferences(getString(R.string.preference_file_key), Context.MODE_PRIVATE);

// 2. activity's default
SharedPreferences pref = getAcitivy().getPreferences(Copntext.MODE_PRIVATE);

// Write
SharedPreferences.Editor editor = pref.edit();
editor.putInt(getString(R.string.saved_high_score), highScore);
editor.commit();

// Read
long highScore = pref.getInt(getString(R.string.saved_high_score), defaultValue);

P2_DeleteFile.java

myFile.delete();
myContext.deleteFile(fileName); // internal storage

// internal storage - deleted with uninstall
// getExternalFilesDir - deleted with uninstall
// getExternalStoragePublicDirectory - kept
// getCacheDir - delete on a regular basis

P2_ExternalStoragePermission.xml

<manifest>
  <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
  <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" /><!-- if only read is needed -->
</manifest>

P2_SavingFiles.java

// internal storage - always available. belongs to app.
// external storage - not always available. world readable
// change [android:installLocation] settings to allow installation on external storage

// easy way
File file = new File(context.getFielsDir(), filename);
File tempFile = new File(context.getCacheDir(), filename);  // system may delete without warning
File photo = new File(Environment.getExternalFilesDir(Environment.DIRECTORY_PICTURES), albumname);  // uninstall-cascade
File photo = new File(Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES), albumname); // uninstall-safe

// another way
FileOutputStream os;
try {
  os = openFileOutput(filename, Context.MODE_PRIVATE);
  os.write(string.getBytes());
  os.close();
} catch (Exception e) {
  e.printStackTrace();
}

// cache
try {
  File file = File.createTempFile(filename, null, context.getCacheDir());
} catch (IOException e) {
  // error creating file
}

// availability of external storage
String state = Environment.getExternalStorageState();
if (Environment.MEDIA_MOUNTED.equals(state) {}  // writable?
if (Environment.MEDIA_MOUNTED.equals(state) || Environemtn.MEDIA_MOUNTED_READ_ONLY.equals(state)) {}  // readable?

P3_SQL.java

public final class FeedReaderContract {
  public FeedReaderContract() {}  // prevent accidental instantiation
  
  public static abstract class FeedEntry implements BaseColumns {
    public static final String TABLE_NAME = "entry";
    public static final String COLUMN_NAME_ENTRY_ID = "entryid";
    public static final String COLUMN_NAME_TITLE = "title";
  }
}