Bernard Bernard - 1 year ago 85
Android Question

Saving Android Activity state

I've been playing around with the Android SDK, and I am a little unclear on saving an application's state. So given this minor re-tooling of the 'Hello, Android' example:


import android.os.Bundle;
import android.widget.TextView;

public class HelloAndroid extends Activity {
/** Called when the activity is first created. */
public void onCreate(Bundle savedInstanceState) {

mTextView = new TextView(this);

if (savedInstanceState == null) {
mTextView.setText("Welcome to HelloAndroid!");
} else {
mTextView.setText("Welcome back.");


private TextView mTextView = null;

I thought that might be all one needed to do for the simplest case, but it always gives me the first message, no matter how I navigate away from the app.

I'm sure it's probably something simple like overriding
or something like that, but I've been poking away in the documentation for 30 minutes or so and haven't found anything obvious, so I would appreciate any help.

Answer Source

You need to override onSaveInstanceState(Bundle savedInstanceState) and write the application state values you want to change to the Bundle parameter like this:

public void onSaveInstanceState(Bundle savedInstanceState) {
  // Save UI state changes to the savedInstanceState.
  // This bundle will be passed to onCreate if the process is
  // killed and restarted.
  savedInstanceState.putBoolean("MyBoolean", true);
  savedInstanceState.putDouble("myDouble", 1.9);
  savedInstanceState.putInt("MyInt", 1);
  savedInstanceState.putString("MyString", "Welcome back to Android");
  // etc.

The Bundle is essentially a way of storing a NVP ("Name-Value Pair") map, and it will get passed in to onCreate() and also onRestoreInstanceState() where you'd extract the values like this:

public void onRestoreInstanceState(Bundle savedInstanceState) {
  // Restore UI state from the savedInstanceState.
  // This bundle has also been passed to onCreate.
  boolean myBoolean = savedInstanceState.getBoolean("MyBoolean");
  double myDouble = savedInstanceState.getDouble("myDouble");
  int myInt = savedInstanceState.getInt("MyInt");
  String myString = savedInstanceState.getString("MyString");

You would usually use this technique to store instance values for your application (selections, unsaved text, etc.).

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