Shared Preferences | Android Developer Tutorial (Part 13)

We saw in an earlier tutorial (Part 12) how data can be stored in SQLDB. However, many applications may provide a way to capture user preferences on the settings of a specific application or an activity. For supporting this, Android provides a simple set of APIs. 

Preferences are typically name value pairs. They can be stored as “Shared Preferences” across various activities in an application (note currently it cannot be shared across processes). Or it can be something that needs to be stored specific to an activity (which is not discussed here). 

The context object lets you retrieve SharedPreferences through the methodContext.getSharedPreferences(). 

In my example, I will set 2 preferences i.e. MyName and MyWallpaper in one activity i.eManageSharedPref.java. Retrieve these values in the next activity – ViewSharedPrefs.java. The second activity displays my preferred name in a list view and also resets the android wallpaper to the image that I had set as a preferred wallpaper in the first activity. When you run this application, if you come back to the home, you will see the wall paper is reset. 

Here is the code in ManageSharesPrefs:

SharedPreferences myPrefs = this.getSharedPreferences("myPrefs",MODE_WORLD_READABLE);
        SharedPreferences.Editor prefsEditor = myPrefs.edit();
        prefsEditor.putString(MY_NAME"Sai");
        prefsEditor.putString(MY_WALLPAPER"f664.PNG");
        prefsEditor.commit();
        
First, I obtain a SharedPreferences object making it readable by all. The first parameter is a name of a file that stores my preferences. This automatically creates the xml file if it does not exist and then stores in the same. 

Next, I edit it. That creates an editor object, using which I input my preferences. Here, for the wall paper, I have put an image name. I also need to push the actual image file into the android storage which I do this way.

adb push <local> <remote>

In this case it is 

adb push f664.PNG /data/misc/wallpaper/f664.PNG

This command creates a folder called wallpaper in /data/misc and copies the f664.PNG file from my current location to the android storage.

When I click the “View Shared Preferences” button, I am taken to the next activity. Here is the code in ViewSharedPrefs that gets executed:

        SharedPreferences myPrefs = this.getSharedPreferences("myPrefs",MODE_WORLD_READABLE);
        String prefName = myPrefs.getString(MY_NAME"nothing");
        String wallPaper = myPrefs.getString(MY_WALLPAPERnull);
        
        if(wallPaper != null) {
            try {
                  Bitmap bm = BitmapFactory.decodeFile("/data/misc/wallpaper/"+wallPaper);
                  Log.d(getClass().getSimpleName(),"Wallpaper name is: "+ wallPaper);
                  setWallpaper(bm);
                  Toast.makeText(this"Wall paper has been changed." +
                              "You may go to the home screen to view the same", Toast.LENGTH_LONG).show();
            } catch (FileNotFoundException fe){
                  Log.e(getClass().getSimpleName(),"File not found");
            } catch (IOException ie) {
                  Log.e(getClass().getSimpleName()," IO Exception");
            }
            
        }
        ArrayList<String> results = new ArrayList<String>();
        results.add("Your Preferred name is: " + prefName);
      this.setListAdapter(new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1,results));

There are 3 steps to understand here:

1.    Step 1: Retrieve the shared prefs data from the object.

        SharedPreferences myPrefs = this.getSharedPreferences("myPrefs",MODE_WORLD_READABLE);
        String prefName = myPrefs.getString(MY_NAME"nothing");
        String wallPaper = myPrefs.getString(MY_WALLPAPERnull);

2.    Step 2: Display the name
        ArrayList<String> results = new ArrayList<String>();
        results.add("Your Preferred name is: " + prefName);
      this.setListAdapter(new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1,results));

3.    Step 3: Reset the wall paper.
        if(wallPaper != null) {
            try {
                  Bitmap bm = BitmapFactory.decodeFile("/data/misc/wallpaper/"+wallPaper);
                  Log.d(getClass().getSimpleName(),"Wallpaper name is: "+ wallPaper);
                  setWallpaper(bm);
                  Toast.makeText(this"Wall paper has been changed." +
                              "You may go to the home screen to view the same", Toast.LENGTH_LONG).show();
            } catch (FileNotFoundException fe){
                  Log.e(getClass().getSimpleName(),"File not found");
            } catch (IOException ie) {
                  Log.e(getClass().getSimpleName()," IO Exception");
            }
            
        }

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