The whole toolkit part III

name: inverse
layout: true
class: center, middle, inverse
---
# The Whole Toolkit Part III
## Storage

Lauren Bricker

CSE 340 Spring 2022
---
layout:false

[//]: # (Outline Slide)
# Goals

- Get input from the user (part 1)
- Produce output for the user (part 2)
- **How to store application specific data** (part 3)

---
# The Whole Toolkit Architecture

- Input
  - Input models (events)
  - Event dispatch
  - Event handling (state machine)
  - Callbacks to application
- Output
  - Interactor Hierarchy design & use
  - Drawing models (`onDraw()`)
  - Layout (`onLayout()` or `XML`)
  - Damage and redraw process
- **Storage**
  - Bundles
  - SharedPreferences

---
# 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](https://developer.android.com/reference/android/os/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.

.footnote[More on [Activity state and ejection from memory](https://developer.android.com/guide/components/activities/activity-lifecycle#asem)]
---
# 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

```java
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!!!"
  }
}
```

---
# 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.

.footnote[From [Android documentation](https://android-doc.github.io/guide/topics/data/data-storage.html)]
---

# Long Term Storage

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

--
... but that is time consuming and would delay the OS launching new things...

---
# Shared Preferences

Stores data in persistent internal memory on the phone.

Like `Bundle`, also stored in Key Value pairs

[SharedPreferences](https://developer.android.com/reference/android/content/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

```java
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)

```java
// 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);

```

---
# Shared Preferences