在活动之间使用SharedPreferences

Question

I have a configuration page which has a form on it. When the button is pressed, I want to save that value to a SharedPreference. This SharedPreference value then needs to be accessed from elsewhere in my app.

I am trying to save the value like the below. I want to save the collectionID so I can use it elsewhere

public class ConfigPage extends Activity {

    public static final String PREFS_NAME = "MyPrefsFile";

    Button   mButton;
    EditText mEdit;
    String collectionID;
    String key = "GregKey";

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.config);
        getActionBar().hide();

        mButton = (Button)findViewById(R.id.setCollection);
        mEdit   = (EditText)findViewById(R.id.collectionName);

        mButton.setOnClickListener(
                new View.OnClickListener()
                {
                    public void onClick(View view)
                    {
                        collectionID = mEdit.getText().toString();
                        Log.d("EditText", collectionID);
                        SharedPreferences settings =
                                getSharedPreferences(PREFS_NAME, 0);
                        SharedPreferences.Editor editor = settings.edit();
                        editor.putString(key, collectionID);
                        editor.commit();
                    }
                });

    }
}

Once it has been saved, I then need to access it in another class, however I can't figure out how to do this. The example above crashes the application at the moment so something isn't quite right

Answer 1

I want to save the collectionID so I can use it elsewhere

Use mButton Button onClick event for saving EditText text in SharedPreferences as :

 mButton.setOnClickListener( new View.OnClickListener()
         {
            public void onClick(View view)
             {
                collectionID = mEdit.getText().toString();
                 Log.d("EditText", collectionID);
                 // save value here in SharedPreferences
                 SharedPreferences settings = 
                            ConfigPage.this.getSharedPreferences(PREFS_NAME, 0);
                 SharedPreferences.Editor editor = settings.edit();
                 editor.putString(collectionID, collectionID);
                 editor.commit();
               }
         });

Answer 2

Your crash occurs because your value is null :

String savedID;

You need to add a value to the variable:

String savedID = "somevalue";

Also, your key is null as long as the Button is not pressed which will also lead to a crash.

The putString(String key, String value) method enables you to store a specific value with a specific key , that can later be used to reaccess the stored value.

Example:

String key = "somekey";
String value = "yourvaluetostore";

SharedPreferences settings = getSharedPreferences(PREFS_NAME, 0);
SharedPreferences.Editor editor = settings.edit();
editor.putString(key, value); // store the value
editor.commit();

In another Activity:

String key = "somekey";
SharedPreferences sharedPreferences = getSharedPreferences(PREFS_NAME, 0);

// get the value "" is default
String value = sharedPreferences.getString(key, ""); 

All you need in the other Activity is the key you stored the value with. With this key, you can pull the correct stored value out of the SharedPreferences . --> The key is needed to identify the value.

Answer 3

Since you are using the part of code :

SharedPreferences settings = getSharedPreferences(PREFS_NAME, 0);
SharedPreferences.Editor editor = settings.edit();
editor.putString(collectionID, savedID);
editor.commit();

Log.d("Saved as", savedID);

in the onCreate method, that translates to

...
editor.putString(null, null);
Log.d("Saved as", null);

Correct your code so that you fill those elements before. I guess you wanted to make the save in the OnClick part

Answer 4

Yes something its not quite right here because as i see you are saving nothing. on shared pref you should have a "key" which will be use to identify the saved value in your example it should be something like this

public class ConfigPage extends Activity {

public static final String PREFS_NAME = "MyPrefsFile";
public static final String COLLECTIONID_KEY = "COLLECTIONID_KEY";
Button   mButton;
EditText mEdit;
String collectionID;
String savedID;

public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.config);
    getActionBar().hide();

    mButton = (Button)findViewById(R.id.setCollection);
    mEdit   = (EditText)findViewById(R.id.collectionName);

    mButton.setOnClickListener(
            new View.OnClickListener()
            {
                public void onClick(View view)
                {
                    collectionID = mEdit.getText().toString();
                    Log.d("EditText", collectionID);
                }
            });

    SharedPreferences settings = getSharedPreferences(PREFS_NAME, 0);
    SharedPreferences.Editor editor = settings.edit();
    editor.putString(COLLECTIONID_KEY, collectionID);
    editor.commit();

    Log.d("Saved as", COLLECTIONID_KEY);
}

}

then to retrieve it :

SharedPreferences sharedPreferences = getSharedPreferences(PREFS_NAME, 0);
String mySavedCollectionID = sharedPreferences.getString(COLLECTIONID_KEY);

and make sure that its done on the Onclick event otherwise you might end up with crash again because after the on-click event in your code the lines below will run anyway and save null!