Question

I have in preferences.xml following EditTextPreference:

  <EditTextPreference
     android:name="@string/pref_test"
     android:defaultValue="0.6"
     android:inputType="numberDecimal"
     android:key="editTestPref"
     android:maxLength="5"
     android:summary=""
     android:title="@string/pref_test" />

In one of my activities I read the value.
But the problem is if the user enters nothing (“”), my app crashes. Sure I could do a if statement in the activity to check if its empty string, but I want to do following:

In Preferences.java I get changes of the preferenceEditText. There I want to set a default value if the user enters “”:

if (preference.getKey().equals("editTestPref")) {

            if(newValue.equals(""))
            {
                final SharedPreferences.Editor prefsEditor = prefs.edit();
                prefsEditor.putString("editTestPref", "1");
                prefsEditor.commit();

                summary = "0.6"; // to update the summary of preference
            }
            else
            {
                summary= (String) newValue;
            }
        }

I also tried this code:

SharedPreferences customSharedPreference = getSharedPreferences(
         "myCustomSharedPrefs", Activity.MODE_PRIVATE);
SharedPreferences.Editor editor = customSharedPreference
                        .edit();
editor.putString("editTestPref", "1");
editor.commit();

Both do not work, they do not update the sharedPreference value. It is still “”.

Answer 1

Implement SharedPreferences.OnSharedPreferenceChangeListener like so:

public class YourPrefsActivity extends PreferenceActivity implements SharedPreferences.OnSharedPreferenceChangeListener {

    // ... your existing code ...

    @Override
    protected void onResume() {
        super.onResume();

        SharedPreferences sharedPreferences = PreferenceManager.getDefaultSharedPreferences(this);
        // Set up a listener whenever a key changes
        sharedPreferences.registerOnSharedPreferenceChangeListener(this);
    }

    @Override
    public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) {
    if ("editTestPref".equals(key)) {
            String val = sharedPreferences.getString("editTestPref", "");
            if (val == null || val.trim().equals("")) {
                val = "0.6"; // <-- your default value
                sharedPreferences.edit().putString(key, val).commit();
            }
        }
    }
}

The method is called when the user changed the preferences value, and checks if he entered an empty string. If so, the value is replaced by your default value.