Java 在Android中使用SharedReference

我试图在我的Things应用程序中使用SharedReferences，但由于某些原因，它总是返回0。我的setter正在使用编辑器记录它推送的正确数据，但是每次读取，即使在重新启动活动之后，也始终为0。我找不到一个原因来解释为什么事情不允许使用SharedReference，即使需要更改权限，所以我有点不知所措。这显然是我的代码，但我不明白为什么

我的目标是使用一个可触摸的文本视图，在触摸时只需更新日期。没有按钮，没有真正的互动，而且简单干净。但如果SharedReference不起作用，这就变得更加困难

在OnCreate中，我使用了各种不同的方法来实例化SharedReferences对象，每次都是徒劳地使用它。我还使用了一个全局和本地编辑器来编辑活动，但没有效果。写入似乎成功，但对于getLong（），读取始终返回0。我从apply（）切换到commit（），认为这可能只是一个时间问题。但是，退出并再次启动活动也不会显示值，它仍然是0

所包含的内容是基于我对Java的了解，在Android文档中找到的最新内容。第一个是我认为与这个问题有关的问题。第二个代码示例是完整的活动

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()));
    }

---

getLong方法返回一个long，您调用的方法的第二个参数不是要填充的引用，而是在找不到首选项的情况下要返回的默认值

---

您的代码根本没有检查共享首选项的返回值。

谢谢。我实际上有两个问题，一个是忽略返回值，另一个是我没有在getter中使用静态字符串常量，并且键不匹配。修复了这两个问题，现在可以正常工作了。非常感谢你。

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();
        }
    };
}

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