Using SharedPreferences in Android Things

Question

I am attempting to use SharedPreferences in my Things application, but it always returns 0 for some reason. My setter is getting is logging tht it pushed the right data using the editor, but every read, even after restarting the activity, is always 0. I can't find a reason why Things wouldn't allow use of SharedPreferences, even with a needed permission change, so I'm kind of at a loss. It's obviously my code, but I can't figure out why.

My goal is to use a TextView which is touchable to simply update the date when touched. No buttons, no real interaction, and it's simple and clean. But if SharedPreferences doesn't work, this gets more difficult.

I have been all over different ways of instantiating the SharedPreferences object, in OnCreate, each time I use it to no effect. I have also used a global and local editor to the Activity, to no effect. Writes seem to succeed, but reads always return 0 for getLong(). I switch from apply() to commit() thinking maybe it's just a timing problem. However, exiting and starting the activity again doesn't show a value either, it's still 0.

What is included is the latest based on what I found in the Android documentation based on what I know about Java. The first is just what I believe to be relevant to the question. The second code sample is the full activity.

public class DataViewActivity extends Activity {
    private static final String TAG = DataViewActivity.class.getSimpleName();

    TextView m_textViewTemperature;
    TextView m_textViewWaterLevel;
    TextView m_textViewIronAddition;
    TextView m_textViewWaterChange;
    TextView m_textViewFilterChange;
    Handler m_exitHandler = new Handler();

    SharedPreferences m_preferences;

    public static final String PREFERENCES = "aquarium";
    public static final String WATER_CHANGE = "waterchange";
    public static final String FILTER_CHANGE = "filterchange";
    public static final String IRON_ADD = "ironaddition";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Log.d(TAG, "onCreate");
        setContentView(R.layout.activity_data_view);

        m_preferences = getSharedPreferences(PREFERENCES, Context.MODE_PRIVATE);
        m_textViewTemperature = findViewById(R.id.textViewTemperatureData);
        m_textViewWaterLevel = findViewById(R.id.textViewWaterLevelData);
        m_textViewFilterChange = findViewById(R.id.textViewFilterChangeDateData);
        m_textViewIronAddition = findViewById(R.id.textViewIronAdditionDateData);
        m_textViewWaterChange = findViewById(R.id.textViewWaterChangeDateData);

        m_textViewWaterChange.setOnTouchListener(new View.OnTouchListener() {
            @SuppressLint("ClickableViewAccessibility")
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                if (event.getAction() == MotionEvent.ACTION_DOWN) {
                    Long time = Calendar.getInstance().getTimeInMillis();
                    SharedPreferences.Editor e = m_preferences.edit();
                    e.putLong(WATER_CHANGE, time);
                    e.commit();
                    Log.i(TAG, "Stored " + time + " to shared preferences for last water change");
                    updateWaterChangeDate();
                }

                return false;
            }
        });
    }

    private void updateWaterChangeDate()
    {
        Calendar c = Calendar.getInstance();
        Long item = m_preferences.getLong("WaterChange", 0);
        Log.d(TAG, "Got " + item + " for last water change millis");
        c.setTimeInMillis(item);
        SimpleDateFormat df = new SimpleDateFormat("EEE, MMM d");
        m_textViewWaterChange.setText(df.format(c.getTime()));
    }

package com.home.pete.aquarium;

import androidx.appcompat.app.AppCompatActivity;
import androidx.localbroadcastmanager.content.LocalBroadcastManager;

import android.annotation.SuppressLint;
import android.app.Activity;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.content.SharedPreferences;
import android.os.Bundle;
import android.os.Handler;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.widget.TextView;

import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Timer;
import java.util.TimerTask;
import java.util.prefs.Preferences;

import static com.home.pete.aquarium.Constants.VIEW_TIMEOUT;
import static java.lang.Long.getLong;

/**
 * Skeleton of an Android Things activity.
 * <p>
 * Android Things peripheral APIs are accessible through the class
 * PeripheralManagerService. For example, the snippet below will open a GPIO pin and
 * set it to HIGH:
 *
 * <pre>{@code
 * PeripheralManagerService service = new PeripheralManagerService();
 * mLedGpio = service.openGpio("BCM6");
 * mLedGpio.setDirection(Gpio.DIRECTION_OUT_INITIALLY_LOW);
 * mLedGpio.setValue(true);
 * }</pre>
 * <p>
 * For more complex peripherals, look for an existing user-space driver, or implement one if none
 * is available.
 *
 * @see <a href="https://github.com/androidthings/contrib-drivers#readme">https://github.com/androidthings/contrib-drivers#readme</a>
 */
public class DataViewActivity extends Activity {
    private static final String TAG = DataViewActivity.class.getSimpleName();

    TextView m_textViewTemperature;
    TextView m_textViewWaterLevel;
    TextView m_textViewIronAddition;
    TextView m_textViewWaterChange;
    TextView m_textViewFilterChange;
    Handler m_exitHandler = new Handler();

    SharedPreferences m_preferences;

    public static final String PREFERENCES = "aquarium";
    public static final String WATER_CHANGE = "waterchange";
    public static final String FILTER_CHANGE = "filterchange";
    public static final String IRON_ADD = "ironaddition";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Log.d(TAG, "onCreate");
        setContentView(R.layout.activity_data_view);

        m_preferences = getSharedPreferences(PREFERENCES, Context.MODE_PRIVATE);
        m_textViewTemperature = findViewById(R.id.textViewTemperatureData);
        m_textViewWaterLevel = findViewById(R.id.textViewWaterLevelData);
        m_textViewFilterChange = findViewById(R.id.textViewFilterChangeDateData);
        m_textViewIronAddition = findViewById(R.id.textViewIronAdditionDateData);
        m_textViewWaterChange = findViewById(R.id.textViewWaterChangeDateData);

        m_textViewWaterChange.setOnTouchListener(new View.OnTouchListener() {
            @SuppressLint("ClickableViewAccessibility")
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                if (event.getAction() == MotionEvent.ACTION_DOWN) {
                    Long time = Calendar.getInstance().getTimeInMillis();
                    SharedPreferences.Editor e = m_preferences.edit();
                    e.putLong(WATER_CHANGE, time);
                    e.commit();
                    Log.i(TAG, "Stored " + time + " to shared preferences for last water change");
                    updateWaterChangeDate();
                }

                return false;
            }
        });

        m_textViewIronAddition.setOnTouchListener(new View.OnTouchListener() {
            @SuppressLint("ClickableViewAccessibility")
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                if (event.getAction() == MotionEvent.ACTION_DOWN) {
                    Long time = Calendar.getInstance().getTimeInMillis();
                    SharedPreferences.Editor e = m_preferences.edit();
                    e.putLong(IRON_ADD, time);
                    e.commit();
                    Log.i(TAG, "Stored " + time + " to shared preferences for last iron addition");
                    updateIronAdditionDate();
                }

                return false;
            }
        });

        m_textViewFilterChange.setOnTouchListener(new View.OnTouchListener() {
            @SuppressLint("ClickableViewAccessibility")
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                if (event.getAction() == MotionEvent.ACTION_DOWN) {
                    Long time = Calendar.getInstance().getTimeInMillis();
                    SharedPreferences.Editor e = m_preferences.edit();
                    e.putLong(FILTER_CHANGE, time);
                    e.commit();
                    Log.i(TAG, "Stored " + time + " to shared preferences for last filter change");
                    updateFilterChangeDate();
                }

                return false;
            }
        });

        LocalBroadcastManager.getInstance(this).registerReceiver(temperatureUpdate, new IntentFilter("temperature"));
        LocalBroadcastManager.getInstance(this).registerReceiver(waterlevelUpdate, new IntentFilter("waterlevel"));

        updateFilterChangeDate();
        updateIronAdditionDate();
        updateWaterChangeDate();

        m_exitHandler.postDelayed(exitViewOnTimeout, VIEW_TIMEOUT);
    }

    @Override
    protected void onDestroy() {
        Log.d(TAG, "onDestroy");
        super.onDestroy();
    }

    private void updateFilterChangeDate()
    {
        Calendar c = Calendar.getInstance();
        Long item = m_preferences.getLong("FilterChange", 0);
        c.setTimeInMillis(item);
        SimpleDateFormat df = new SimpleDateFormat("EEE, MMM d");
        m_textViewFilterChange.setText(df.format(c.getTime()));
    }

    private void updateWaterChangeDate()
    {
        Calendar c = Calendar.getInstance();
        Long item = m_preferences.getLong("WaterChange", 0);
        Log.d(TAG, "Got " + item + " for last water change millis");
        c.setTimeInMillis(item);
        SimpleDateFormat df = new SimpleDateFormat("EEE, MMM d");
        m_textViewWaterChange.setText(df.format(c.getTime()));
    }

    private void updateIronAdditionDate()
    {
        Calendar c = Calendar.getInstance();
        Long item = m_preferences.getLong("IronAddition", 0);
        c.setTimeInMillis(item);
        SimpleDateFormat df = new SimpleDateFormat("EEE, MMM d");
        m_textViewIronAddition.setText(df.format(c.getTime()));
    }

    public void exitView(View view)
    {
        Log.d(TAG, "Closing view");
        m_exitHandler.removeCallbacks(exitViewOnTimeout);
        finish();
    }

    private BroadcastReceiver temperatureUpdate = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent)
        {
            Double value = intent.getDoubleExtra("ACTION", 0.0);
            m_textViewTemperature.setText(value.toString() + " \u2109");
        }
    };

    private BroadcastReceiver waterlevelUpdate = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent)
        {
            Integer value = intent.getIntExtra("ACTION", 0);
            String text;
            if (value > 2760)
                text = "full";
            else if (value > 2750)
                text = "-1 cm";
            else if (value > 2730)
                text = "-2 cm";
            else
                text = value.toString();

            m_textViewWaterLevel.setText(text);
        }
    };

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

    private Runnable exitViewOnTimeout = new Runnable() {
        @Override
        public void run() {
            Log.d(TAG, "Closing view due to timeout handler");
            finish();
        }
    };
}

Logging shows that a valid millis value is stored in the Long in the OnTouchListener, which is called when I touch the TextView. Every call to updateWaterChangeDate() logs 0 for item and the Date is always the 1st of 1970.

2019-06-22 09:20:20.483 2614-2614/com.home.pete.aquarium I/DataViewActivity: Stored 1561213220471 to shared preferences for last water change
2019-06-22 09:20:20.484 2614-2614/com.home.pete.aquarium D/DataViewActivity: Got 0 for last water change millis
...
2019-06-22 09:20:25.647 2614-2614/com.home.pete.aquarium D/DataViewActivity: onDestroy
2019-06-22 09:20:26.710 2614-2614/com.home.pete.aquarium D/MainActivity: Viewing settings
2019-06-22 09:20:26.737 2614-2614/com.home.pete.aquarium D/DataViewActivity: onCreate
2019-06-22 09:20:26.834 2614-2614/com.home.pete.aquarium D/DataViewActivity: Got 0 for last water change millis

Answer 1

The method getLong returns a long, the second parameter to the method you're calling is not a reference to be filled, but the default value to be returned in case the preference is not found.

Your code is simply not checking the return value from shared preferences.