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One way to persist data in Android is by using SharedPreferences. In this video we'll introduce and start implementing SharedPreferences.
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Now that we know about
the activity lifecycle,
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we can start to learn about
saving data in Android.
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Within Android, there are several
approaches for us to save our data and
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we cover them in detail in another
course on data persistence.
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Of these approaches, the easiest
one to use is shared preferences.
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Shared preferences are used to
store key value pairs for our apps.
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Some typical uses for a shared preference
could be to save a user's name,
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keep track of which theme a user prefers,
or
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to store a counter of how many
times a user has opened our app.
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Let's explore shared preferences
with a new application.
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I'm going to call the app
SharedpreferencesApp and then hit Next.
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Hit Next again, pick Empty Activity,
hit Next and then click Finish.
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In this app, we're going to create
an edit text that saves its value
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even if we completely close the app.
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Let's start by creating an edit text.
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In activity_main.xml,
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which is in the res folder in
the layout directory, let's start
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by getting rid of the Hello World text
view by clicking it and hitting Delete.
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Then let's add a plain text text field to
the top of our app centered horizontally.
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Next, let's click up here to change
the layout width to match parent and
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then scroll down over here
to make sure we have an ID.
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Great!
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Lastly, let's create a field for
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our edit text inside mainactivity.java.
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We'll write private EditText and
we'll call it mEditText.
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Alt Enter to import edit text.
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Then in the bottom of onCreate, we'll type
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mEditText = in parentheses EditText,
findviewbyID,
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and the ID of our edit text,
which is editText.
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Looks good.
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Before we go on to implementing shared
preferences, I'm going to quickly run
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the app so I can showcase a behavior
you wouldn't normally expect.
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Here we have the app.
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I'm going to type in some text and
then rotate the app.
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[SOUND] Knowing that Android destroys and
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recreates activities when they rotate and
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that we didn't implement anything
that would save this value,
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this text should not
persist through a rotation.
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So why did it persist through a rotation?
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It turns out that any views,
text views, buttons, check boxes,
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etc., that have a unique ID would
have their instant state saved and
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restored automatically by Android.
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Cool, but
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if we leave the activity by
hitting the back button and
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then open a new activity or a new instance
of our app, we get an empty edit text.
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We still need to use shared preferences
to persist our data through the activity
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being destroyed.
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Let's start by creating a field for
our shared preferences object.
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At the top of the class, type private
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SharedPreferences and
we'll call it m SharedPreferences.
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Then and on Create, let's initialize
our shared preferences object
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by typing mSharedPreferences
= getSharedPreferences.
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We can see that the first
parameter is a string called Name.
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This will be the name of our
shared preferences file.
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It's usually a good idea to set this
to your package name plus .preferences.
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Just make sure that your
preferences name will be unique
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among all the SharedPreferences out there.
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The second parameter is an integer,
which represents the mode.
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We'll use mode private so
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our shared preferences file can be
accessed by only our application.
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Also, all of the other
modes are deprecated.
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Now that we know what parameters to use,
let's finish creating our object.
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For the first parameter,
type PREFS_FILE in
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all caps to let Android Studio know that
this is a private static final string.
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And then type ,_Context.MODE_PRIVATE for
the mode.
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Next, let's put our cursor back on
PREFS_FILE and hit Alt Enter to have
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Android Studio generate the variable, and
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now we can type in the value
we talked about earlier.
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The package name, which for
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me is
com.teamtreehouse.sharedpreferencesapp and
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ahead.preferences.
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Great, now that we have access
to our shared preferences,
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let's store our string.
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All share preferences objects have
an editor, and we need to use that editor,
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when we want to add any key value
pairs to our shared preferences.
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Let's create a field for
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our shared preferences editor by
going to the top of the class and
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typing private SharedPreferences.Editor
and we'll call it mEditor.
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Then, let's initialize our field and
the bottom of onCreate by typing MEditor
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= mSharedPreferences.edit.
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We're ready to start using this editor but
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let's take a short break and then see how
to use this to save and retrieve data.
6:31
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