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Android Android Activity Lifecycle Introducing SharedPreferences Saving and Retrieving Data with SharedPreferences

Posted by Ja'Nel Johnson
Ja'Nel Johnson
10,314 Points

Can someone help me make sense of Shared Preferences? I can't figure out the challenges.

Challenge 1: We'd like to persist the value of a CheckBox by using SharedPreferences. Start by declaring a constant for the file name of our preferences called PREFS_FILE. Then declare a constant for the key we'll require; call it KEY_CHECKBOX.

I went back to the video and followed along, but my answer is still wrong.

The error message keeps telling me to declare all constants.

Any suggestions?

MainActivity.java 
import android.view.View;
import android.os.Bundle;

public class MainActivity extends Activity {
  private static final STRING PREFS_FILE = "KEY_CHECKBOX";


  public CheckBox mCheckBox;

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);



    mCheckBox = (CheckBox) findViewById(R.id.checkBox);
  }
}

5 Answers

Kevin Faust
Kevin Faust
15,353 Points
Kevin Faust
Kevin Faust
15,353 Points

Hey Ja'Nel,

First thing I'd like to point out is that it should be "String" not "STRING"

Secondly, our PREFS_FILE constant should be equal to our packagename + .preferences. Remember that? It's just good naming convention.

Thirdly, we need a constant variable that holds the value of the state of our checbox. That is where you put KEY_CHECKBOX

In more visual terms look below:

private static final String PREFS_FILE = "com.packagename.preferences";
  private static final String KEY_CHECKBOX = "KEY_CHECKBOX";

Hope that helped!

SharedPreferences was pretty tricky for me at first hehe

Ja'Nel Johnson
Ja'Nel Johnson
10,314 Points

Hey, Kevin!

Would you mind helping me with the next part? I'm following along but my answer isn't right.

Challenge 2: Now declare a SharedPreferences field named mSharedPreferences and an Editor field named mEditor. Then initialize both of these fields in the onCreate method.

import android.view.View;
import android.os.Bundle;

public class MainActivity extends Activity {
  private Editor mEditor;
  private SharedPreferences mSharedPreferences;
  private static final String PREFS_FILE = "com.packagename.preferences";
  private static final String KEY_CHECKBOX = "KEY_CHECKBOX";

  public CheckBox mCheckBox;

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    mCheckBox = (CheckBox) findViewById(R.id.checkBox);
    mEditor = getEditor();
    mSharedPreferences = getSharedPreferences();
  }
}
Kevin Faust
Kevin Faust
15,353 Points
Kevin Faust
Kevin Faust
15,353 Points

//Edited code for markup

Kevin Faust
Kevin Faust
15,353 Points
Kevin Faust
Kevin Faust
15,353 Points

Hi Tina Bryan,

Context.MODE_PRIVATE has nothing to do with public/private variables. This is simply a paramater that the getSharedPreferences requires

[ http://goo.gl/g0GTqz ]

From the android docs, "Use 0 or MODE_PRIVATE for the default operation, MODE_WORLD_READABLE and MODE_WORLD_WRITEABLE to control permissions."

Tina Maddox
Tina Maddox
28,102 Points
Tina Maddox
Tina Maddox
28,102 Points

Thanks Kevin! Not sure why I didn't get this notice until now but thank you for the information!

Kevin Faust
Kevin Faust
15,353 Points
Kevin Faust
Kevin Faust
15,353 Points

Hi Ja'Nel,

It should be 

  private SharedPreferences.Editor mEditor;

instead of just 

  private Editor mEditor;

Secondly your forgetting to put some things inside your getSharedPreferences("code should be in here")

mSharedPreferences = getSharedPreferences(PREFS_FILE, Context.MODE_PRIVATE);

Do you remember that? And then we initialize the mEditor variable by calling edit() on our mSharedPreferences

 mEditor = mSharedPreferences.edit();
Tina Maddox
Tina Maddox
28,102 Points
Tina Maddox
Tina Maddox
28,102 Points

Hello Kevin (and Ja'Nel, whats up girl? :) ),

I am a little confused with the second line above:

mSharedPreferences = getSharedPreferences(PREFS_FILE, Context.MODE_PRIVATE);

When we declared it was 'public', so why is it 'private' here?

Carl Sergile
Carl Sergile
16,570 Points
Carl Sergile
Carl Sergile
16,570 Points

Hey having a hard time with this problem. On the second out of the four task. I've created the variables. I guess I just don't know where to plug it in. Here is my code:

import android.view.View;
import android.os.Bundle;

public class MainActivity extends Activity {

  public CheckBox mCheckBox;
    private static final String PREFS_FILE = "com.packagename.preferences";
  private static final String KEY_CHECKBOX = "KEY_CHECKBOX";
  private SharedPreferences mSharedPreferences;
  private SharedPreferences.Editor mEditor;

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    mCheckBox = (CheckBox) findViewById(R.id.checkBox);
    mEditor = mSharedPreferences.edit();
    mSharedPreferences = getSharedPreferences(PREFS_FILE, Context.MODE_PRIVATE);
  }
}

UPDATED. Still showing a null error.

Kevin Faust
Kevin Faust
15,353 Points
Kevin Faust
Kevin Faust
15,353 Points

my account is paused so i cant see what the question for part 2 is asking (if you could copy and paste it that would be helpful).

in terms of posting code here, just wrap your code in three black ticks with the language ur using. so for example:

```java
code```

btw you should do:

//swap order
mSharedPreferences = getSharedPreferences(PREFS_FILE, Context.MODE_PRIVATE);
mEditor = mSharedPreferences.edit();

because your calling edit() on mSharedPreferences when mSharedPreferences isnt initialized yet

Julie Carere
Julie Carere
3,858 Points
Julie Carere
Julie Carere
3,858 Points

One thing I noticed was missing on the answers here that I found in the video, is to put private SharedPreferences mSharedPreferences;

So a complete correct solution is here:

import android.view.View;
import android.os.Bundle;

public class MainActivity extends Activity {
  private SharedPreferences mSharedPreferences;
  private SharedPreferences.Editor mEditor;  
  public CheckBox mCheckBox;
  private static final String PREFS_FILE = "com.packagename.preferences";
  private static final String KEY_CHECKBOX = "KEY_CHECKBOX";

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    mCheckBox = (CheckBox) findViewById(R.id.checkBox);
    mSharedPreferences = getSharedPreferences(PREFS_FILE, Context.MODE_PRIVATE);
    mEditor = mSharedPreferences.edit();
  }
}
TERRENCE MAVHUNGA
TERRENCE MAVHUNGA
6,053 Points
TERRENCE MAVHUNGA
TERRENCE MAVHUNGA
6,053 Points

thank you Kevin