Today's goals

• Administrivia
  • Layout part 3-4 & reflection due Thur 26-Jan
  • Practice quiz 3 out, due Sunday 10pm
• Quick Layout demo with Spot the Heron (branch: layout-ii)
• Questions on last of Properties of People - Vision?
• Storage
  • Bundles
  • Shared Preferences
• Android Security

Demo of Programatic Layout

One thing that we didn't cover well is how to set up layout params/constraints programatically. So let's demo it now! To follow along:

1. Clone Spot the Heron if you have not already
2. Switch to branch layout-ii using git checkout layout-ii
   • If you made changes and it complains about conflicts you may need to
     • commit your changes to your local repo (git add/git commit) but don't git push (you won't be able to)
     • do a git stash push to temporarily store your changes, then git stash pop later to get them back*
     • re-clone STH in a different directory

Here are resources on git branches and git conflict resolution

Recap

• We created a toolbar in a separate .xml file.
• We used the inflater to turn the .xml button bar into a "live" View object.
• We created LayoutParams to lay the button bar out correctly in the parent
• We found the main parent view by it's id.
• We attached the button bar View to the parent.

Today's goals

• Administrivia
  • Layout part 3-4 & reflection due Thur 26-Jan
  • Practice quiz 3 out, due Sunday 10pm
• Quick Layout demo with Spot the Heron (branch: layout-ii)
• Questions on last of Properties of People - Vision?
• Storage
  • Bundles
  • Shared Preferences
• Android Security

So you got lots of apps..

So you got lots of apps..

So you got lots of apps..

Storage options

There are two main types different storage options to save data -

• Short term volatile memory
  • Data that goes away when the phone is turned off
• Long term memory
  • Data that can be recovered when the phone is turned off and back on

Short Term Storage option

Bundle

• Usually stores a small amount of data
• Saved RIGHT before the memory is cleared.
• Typically used when you want to safely transfer data between activities or between an activity and a fragment.
• The Bundle is sent back when the activity starts running again.
• A Bundle is destroyed if the user force quits the app/phone is turned off.

More on Activity state and ejection from memory

What is in the Bundle?

You, the application developer, decides what needs to be stored

Values are mapped to unique KEYS (for set/retrieve)

The Bundle is like a Map<String, Object> that only supports Serializable objects (like primitives and String)

Bundles: Code Example

public abstract class MainActivity extends AppCompatActivity {
  @Override
  public void onSaveInstanceState(Bundle outState) {
      super.onSaveInstanceState(outState);
      outState.putString("OUR_KEY", "bundles? bundles!!!");
  }
  @Override
  protected void onRestoreInstanceState(Bundle savedInstanceState) {
      super.onRestoreInstanceState(savedInstanceState);
      String whatWeSaved = savedInstanceState.getString("OUR_KEY");
      // whatWeSaved would contain "bundles? bundles!!!"
  }
}

Modifying Doodle

To save which Tab/Activity shown in Doodle we could modify AbstractMainActivity.java to store it in a Bundle

protected static final String CURRENT_TAB_ID_KEY = "ACTIVITY_TAB_ID";
private TabView mNav = findViewById(R.id.bottom_nav);
protected void onSaveInstanceState(Bundle outState) {
  super.onSaveInstanceState(outState);
  // Get the current tab id, and store it with CURRENT_TAB_ID_KEY
  outState.putInt(CURRENT_TAB_ID_KEY, getTabId());
}
protected void onRestoreInstanceState(Bundle outState) {
  // get the tab from the bundle at CURRENT_TAB_ID_KEY, defaulting to
  // R.id.action_part_1 & set the nav accordinly!
  int current = outState.getInt(CURRENT_TAB_ID_KEY, R.id.action_part_1);
  mNav.setSelectedItemId(current);
}

We will see this more in Accessibility

Bundles & Code

• Bundle management is occuring at the Activity layer, not to be confused with any individual View.
• When the user closes the app, right before it closes and its memory is cleared, Android invokes onSaveInstanceState(Bundle outState) on the activity, providing a reference to the activity for the app to save values into.
• When the user opens the app again, Android invokes onRestoreInstanceState(Bundle savedInstanceState) returning the same bundle from earlier.

(Read more here)

Bundles & Code

• Bundle data is transient - it will go away if the app is completely unloaded from memory.
  • Typically small amounts of data.
  • Used to share information between activities.

How can we store things for longer??!?!?

Long Term Storage

Longer term, persistent storage stay around even if the phone is turned off.

Shared Preferences

• Store private primitive data in key-value pairs. Internal Storage
• Store private data on the device memory. External Storage
• Store public data on the shared external storage. SQLite Databases
• Store structured data in a private database. Network Connection
• Store data on the web with your own network server.

From Android documentation

Long Term Storage

Note that the app could write/read its state to longer term storage whenever it is being closed/opened ...

Shared Preferences

Stores data in persistent internal memory on the phone.

Like Bundle, also stored in Key Value pairs

SharedPreferences documentation

Shared Preferences

To see what is in your shared preferences

1. start the Device File Explorer (View->Tool windows->Device File Explorer)
2. Use the toggles to open up the following folders

data
  data
    <packagename> for your app, such as cse340.askforhelp
      shared_prefs
        <packagename>.PREFERENCES.xml

Shared Preferences

Creating the Shared Preferences File

protected SharedPreferences getPrefs() {
  if ( mSharedPreferences == null ) {
      try {
          Context context = getApplicationContext();
          mSharedPreferences = context.getSharedPreferences(context.getPackageName() + ".PREFERENCES",
                  Context.MODE_PRIVATE);
      } catch (Exception e) {
          //failed to edit shared preferences file
          showToast(R.string.shared_pref_error);
      }
  }
  return mSharedPreferences;
}

Shared Preferences

Saving to/restoring from the Shared Preferences file.

Example (if we chose to store in SharedPreferences)

// setting data
SharedPreferences.Editor editor = getPrefs().edit();
editor.putInt(CURRENT_TAB_ID_KEY, mTabId);
editor.apply();  // have to force the write.
// getting data, the last parameter is the default.
mTabId = getPrefs().getInt(CURRENT_TAB_ID_KEY, 1);

We will see this in Accessibility

Shared Preferences

Other types you can read/write

editor.putBoolean("key", booleanValue);
editor.putInt("key", intValue);
editor.putString("key", strintValue);
editor.putStringSet(key, stringSetValue);

END OF DECK