在Android Things中使用SharedPreferences

Question

我正在嘗試在我的Things應用程序中使用SharedPreferences，但是由於某種原因它總是返回0。 我的設置者正在使用它記錄編輯器記錄的正確數據，但是每次讀取（即使在重新啟動活動之后也始終為0）。我無法找到事物為何不允許使用SharedPreferences的原因，即使使用需要更改權限，所以我有點茫然。 顯然，這是我的代碼，但是我不知道為什么。

我的目標是使用可觸摸的TextView，以在觸摸時簡單地更新日期。 沒有按鈕，沒有真正的交互，並且簡單干凈。 但是，如果SharedPreferences不起作用，這將變得更加困難。

每次使用OnCreate都無效時，我一直在使用不同的方法來實例化OnCreate中的SharedPreferences對象。 我也對Activity使用了全局和本地編輯器，但沒有任何效果。 寫入似乎成功，但是讀取總是為getLong（）返回0。 我從apply（）切換到commit（），這可能只是時間問題。 但是，再次退出並開始活動也不顯示任何值，它仍然是0。

根據我對Java的了解，所包含的內容基於我在Android文檔中找到的最新內容。 首先是我認為與這個問題有關的東西。 第二個代碼示例是完整活動。

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();
        }
    };
}

記錄顯示有效的Millis值存儲在OnTouchListener的Long中，當我觸摸TextView時會調用它。 每次對updateWaterChangeDate（）的調用都會為該項目記錄0，而Date始終是1970年1月1日。

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

方法getLong返回一個很長的第二個參數，該參數不是要填充的引用，而是在未找到首選項的情況下返回的默認值。

您的代碼只是不檢查共享首選項的返回值。