Fragment中第一次调用SharedPreferences为空
SharedPreferences are empty when called for the first time in Fragment
我有一个示例 android 应用程序，根据位置（邮政编码）和在设置 (SharedPreference) 中设置的温度单位，应用程序显示 7 天的天气。
应用程序第一次获取温度并检查SharedPreference中设置的温度单位时，它似乎是空的并且isMetric设置为TRUE。 Utility.isMetric 可以改进以表示没有从 SharedPreference 获取数据，但我的问题是为什么在 Utility.isMetric 从 ForecastFragment 的 onCreateView 中第一次调用时 SharedPreference 为空？
Utility.isMetric 访问 SharedPreference
SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(context);
ForecastFragment 调用 Utility.isMetric
boolean isMetric = Utility.isMetric(getActivity());
我有 logcat 展示了这种行为，如果您想看到，请告诉我。
因为没有最大限制。字符，完整代码可以在 https://github.com/gosaliajigar/CSC519/tree/master/CSC519-HW6
访问
预测片段
public class ForecastFragment extends Fragment implements LoaderCallbacks<Cursor> {
private SimpleCursorAdapter mForecastAdapter;
private static final int FORECAST_LOADER = 0;
private String mLocation;
// For the forecast view we're showing only a small subset of the stored data.
// Specify the columns we need.
private static final String[] FORECAST_COLUMNS = {
// In this case the id needs to be fully qualified with a table name, since
// the content provider joins the location & weather tables in the background
// (both have an _id column)
// On the one hand, that's annoying. On the other, you can search the weather table
// using the location set by the user, which is only in the Location table.
// So the convenience is worth it.
WeatherEntry.TABLE_NAME + "." + WeatherEntry._ID,
WeatherEntry.COLUMN_DATETEXT,
WeatherEntry.COLUMN_SHORT_DESC,
WeatherEntry.COLUMN_MAX_TEMP,
WeatherEntry.COLUMN_MIN_TEMP,
LocationEntry.COLUMN_LOCATION_SETTING
};
// These indices are tied to FORECAST_COLUMNS. If FORECAST_COLUMNS changes, these
// must change.
public static final int COL_WEATHER_ID = 0;
public static final int COL_WEATHER_DATE = 1;
public static final int COL_WEATHER_DESC = 2;
public static final int COL_WEATHER_MAX_TEMP = 3;
public static final int COL_WEATHER_MIN_TEMP = 4;
public static final int COL_LOCATION_SETTING = 5;
public ForecastFragment() {
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Add this line in order for this fragment to handle menu events.
setHasOptionsMenu(true);
}
@Override
public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
inflater.inflate(R.menu.forecastfragment, menu);
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.action_refresh) {
updateWeather();
return true;
}
return super.onOptionsItemSelected(item);
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
final String[] columns = {WeatherEntry.COLUMN_DATETEXT,
WeatherEntry.COLUMN_SHORT_DESC,
WeatherEntry.COLUMN_MAX_TEMP,
WeatherEntry.COLUMN_MIN_TEMP
};
final int[] viewIDs = {R.id.list_item_date_textview,
R.id.list_item_forecast_textview,
R.id.list_item_high_textview,
R.id.list_item_low_textview
};
// The SimpleCursorAdapter will take data from the database through the
// Loader and use it to populate the ListView it's attached to.
mForecastAdapter = new SimpleCursorAdapter(
getActivity(),
R.layout.list_item_forecast,
null,
columns,
viewIDs,
0);
mForecastAdapter.setViewBinder(new SimpleCursorAdapter.ViewBinder() {
@Override
public boolean setViewValue(View view, Cursor cursor, int columnIndex) {
boolean isMetric = Utility.isMetric(getActivity());
switch (columnIndex) {
case COL_WEATHER_MAX_TEMP: {
String high = Utility.formatTemperature(
cursor.getDouble(cursor.getColumnIndex(WeatherEntry.COLUMN_MAX_TEMP)), isMetric);
((TextView) view).setText(high);
return true;
}
case COL_WEATHER_MIN_TEMP: {
// we have to do some formatting and possibly a conversion
String low = Utility.formatTemperature(
cursor.getDouble(cursor.getColumnIndex(WeatherEntry.COLUMN_MIN_TEMP)), isMetric);
((TextView) view).setText(low);
return true;
}
case COL_WEATHER_DATE: {
String dateString = Utility.formatDate(
cursor.getString(cursor.getColumnIndex(WeatherEntry.COLUMN_DATETEXT)));
((TextView) view).setText(dateString);
return true;
}
}
return false;
}
});
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
// Get a reference to the ListView, and attach this adapter to it.
ListView listView = (ListView) rootView.findViewById(R.id.listview_forecast);
listView.setAdapter(mForecastAdapter);
listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> adapterView, View view, int position, long l) {
Cursor cursor = mForecastAdapter.getCursor();
if (cursor != null && cursor.moveToPosition(position)) {
Intent intent = new Intent(getActivity(), DetailActivity.class)
.putExtra(DetailActivity.DATE_KEY, cursor.getString(COL_WEATHER_DATE));
startActivity(intent);
}
}
});
return rootView;
}
@Override
public void onActivityCreated(Bundle savedInstanceState) {
getLoaderManager().initLoader(FORECAST_LOADER, null, this);
super.onActivityCreated(savedInstanceState);
}
private void updateWeather() {
String location = Utility.getPreferredLocation(getActivity());
// update weather only if location is not an EMPTY string
if (location != null
&& location.length() > 0) {
new FetchWeatherTask(getActivity()).execute(location, SettingsActivity.FORECAST_DAYS);
}
}
@Override
public void onResume() {
super.onResume();
if (mLocation != null && !mLocation.equals(Utility.getPreferredLocation(getActivity()))) {
getLoaderManager().restartLoader(FORECAST_LOADER, null, this);
}
}
@Override
public Loader<Cursor> onCreateLoader(int id, Bundle args) {
// This is called when a new Loader needs to be created. This
// fragment only uses one loader, so we don't care about checking the id.
// To only show current and future dates, get the String representation for today,
// and filter the query to return weather only for dates after or including today.
// Only return data after today.
String startDate = WeatherContract.getDbDateString(new Date());
// Sort order: Ascending, by date.
String sortOrder = WeatherEntry.COLUMN_DATETEXT + " ASC";
mLocation = Utility.getPreferredLocation(getActivity());
if (mLocation == null || mLocation.length() == 0) {
mLocation = "00000";
}
Uri weatherForLocationUri = WeatherContract.WeatherEntry.buildWeatherLocationWithStartDate(mLocation, startDate);
Log.d(getString(R.string.app_name), weatherForLocationUri.toString());
// Now create and return a CursorLoader that will take care of
// creating a Cursor for the data being displayed.
return new CursorLoader(
getActivity(),
weatherForLocationUri,
FORECAST_COLUMNS,
null,
null,
sortOrder
);
}
@Override
public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
mForecastAdapter.swapCursor(data);
}
@Override
public void onLoaderReset(Loader<Cursor> loader) {
mForecastAdapter.swapCursor(null);
}
}
实用程序
public class Utility {
public static String getPreferredLocation(Context context) {
SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(context);
return prefs.getString(context.getString(R.string.pref_location_key),
context.getString(R.string.pref_location_default));
}
public static boolean isMetric(Context context) {
SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(context);
return prefs.getString(context.getString(R.string.pref_units_key),
context.getString(R.string.pref_units_metric))
.equals(context.getString(R.string.pref_units_metric));
}
static String formatTemperature(double temperature, boolean isMetric) {
double temp;
if ( !isMetric ) {
temp = 9*temperature/5+32;
} else {
temp = temperature;
}
return String.format("%.0f", temp);
}
static String formatDate(String dateString) {
Date date = WeatherContract.getDateFromDb(dateString);
return DateFormat.getDateInstance().format(date);
}
}
我已将 logcat 放入两个文件（Utility 和 ForecastFragment）中以演示该问题。这是 logcat 首次加载 ForecastFragment onCreateView 时，安装应用程序时。
07-05 17:35:57.562 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:35:57.563 21604-21604/com.example.android.weather.app D/JIGAR: isMetric true
这是 logcat 当 ForecastFragment onCreateView 加载时，按下刷新按钮后。
07-05 17:36:44.433 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.435 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.435 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.436 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.445 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.449 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.450 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.452 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.458 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.458 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.458 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.458 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.459 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.460 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.460 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.460 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.461 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.461 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.461 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.461 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.462 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.462 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.462 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.463 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.463 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.464 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.464 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.464 21604-21604/com.example.android.weather.app D/JIGAR: {}
我现在已经从以上两个位置删除了 Log.d 语句，但非常欢迎您放置日志语句。
注意：这是一个家庭作业应用程序，文件中显示了 TO DO 及其完整的应用程序，但在玩应用程序和理解代码时，我在应用程序中发现了这个错误并试图理解它发生的原因。这是作业或任何提交的 NOT 部分。
你的sharedPreferences为空的原因是你一开始没有成功输入任何东西。
我建议以这种方式使用 sharedPreferences，因为这对我有用：
import android.content.SharedPreferences;
在你的函数中：
SharedPreferences preferences = getApplicationContext().getSharedPreferences("AppPref", MODE_PRIVATE);
SharedPreferences.Editor editor = preferences.edit();
editor.putString("**Input your data here**", **tag your data/give it a name*);//example editor.putString("userPassword", password);
editor.commit();//this one places your string into the sharedpreferences instance you created
为了在创建时访问您的共享首选项：
private String data; //this receives your data from sharedpref
@Override
protected void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
SharedPreferences conn = getSharedPreferences("AppPref", MODE_PRIVATE);
data = conn.getString("**your data tag**","");
}
希望这对您有所帮助。如果您希望存储会话中的值，则需要专门为运行时输入的数据创建一个 sharedpreferences 实例。我不太擅长技术解释，所以如果您有任何疑问，请要求澄清。
感谢 Dennis 和 Kaze，我的 android 应用程序正在 SettingActivity extends PreferenceActivity 中的 addPreferencesFromResource(R.xml.pref_general) 帮助下从 xml 文件加载默认共享首选项activity 当有人点击“设置”按钮时它会启动，因此在按下“设置”按钮之前不会填充共享首选项。
你关于填充默认首选项的问题让我研究了它是如何填充的，它应该使用 PreferenceManager.setDefaultValues 在 ForecastFragment onCreate 中填充，如下所示......
PreferenceManager.setDefaultValues(context, R.xml.pref_general, false);
这解决了我的问题。我会给你的答案投票！谢谢
您应该使用 PreferenceManager 中的以下方法从 xml 加载默认值（正如您在评论中所述，默认值是从 xml 加载的）。
static void setDefaultValues(Context context, int resId, boolean readAgain)
Sets the default values from an XML preference file by reading the values defined by each Preference item's android:defaultValue attribute.
我有一个示例 android 应用程序，根据位置（邮政编码）和在设置 (SharedPreference) 中设置的温度单位，应用程序显示 7 天的天气。
应用程序第一次获取温度并检查SharedPreference中设置的温度单位时，它似乎是空的并且isMetric设置为TRUE。 Utility.isMetric 可以改进以表示没有从 SharedPreference 获取数据，但我的问题是为什么在 Utility.isMetric 从 ForecastFragment 的 onCreateView 中第一次调用时 SharedPreference 为空？
Utility.isMetric 访问 SharedPreference
SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(context);
ForecastFragment 调用 Utility.isMetric
boolean isMetric = Utility.isMetric(getActivity());
我有 logcat 展示了这种行为，如果您想看到，请告诉我。
因为没有最大限制。字符，完整代码可以在 https://github.com/gosaliajigar/CSC519/tree/master/CSC519-HW6
访问预测片段
public class ForecastFragment extends Fragment implements LoaderCallbacks<Cursor> {
private SimpleCursorAdapter mForecastAdapter;
private static final int FORECAST_LOADER = 0;
private String mLocation;
// For the forecast view we're showing only a small subset of the stored data.
// Specify the columns we need.
private static final String[] FORECAST_COLUMNS = {
// In this case the id needs to be fully qualified with a table name, since
// the content provider joins the location & weather tables in the background
// (both have an _id column)
// On the one hand, that's annoying. On the other, you can search the weather table
// using the location set by the user, which is only in the Location table.
// So the convenience is worth it.
WeatherEntry.TABLE_NAME + "." + WeatherEntry._ID,
WeatherEntry.COLUMN_DATETEXT,
WeatherEntry.COLUMN_SHORT_DESC,
WeatherEntry.COLUMN_MAX_TEMP,
WeatherEntry.COLUMN_MIN_TEMP,
LocationEntry.COLUMN_LOCATION_SETTING
};
// These indices are tied to FORECAST_COLUMNS. If FORECAST_COLUMNS changes, these
// must change.
public static final int COL_WEATHER_ID = 0;
public static final int COL_WEATHER_DATE = 1;
public static final int COL_WEATHER_DESC = 2;
public static final int COL_WEATHER_MAX_TEMP = 3;
public static final int COL_WEATHER_MIN_TEMP = 4;
public static final int COL_LOCATION_SETTING = 5;
public ForecastFragment() {
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Add this line in order for this fragment to handle menu events.
setHasOptionsMenu(true);
}
@Override
public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
inflater.inflate(R.menu.forecastfragment, menu);
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.action_refresh) {
updateWeather();
return true;
}
return super.onOptionsItemSelected(item);
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
final String[] columns = {WeatherEntry.COLUMN_DATETEXT,
WeatherEntry.COLUMN_SHORT_DESC,
WeatherEntry.COLUMN_MAX_TEMP,
WeatherEntry.COLUMN_MIN_TEMP
};
final int[] viewIDs = {R.id.list_item_date_textview,
R.id.list_item_forecast_textview,
R.id.list_item_high_textview,
R.id.list_item_low_textview
};
// The SimpleCursorAdapter will take data from the database through the
// Loader and use it to populate the ListView it's attached to.
mForecastAdapter = new SimpleCursorAdapter(
getActivity(),
R.layout.list_item_forecast,
null,
columns,
viewIDs,
0);
mForecastAdapter.setViewBinder(new SimpleCursorAdapter.ViewBinder() {
@Override
public boolean setViewValue(View view, Cursor cursor, int columnIndex) {
boolean isMetric = Utility.isMetric(getActivity());
switch (columnIndex) {
case COL_WEATHER_MAX_TEMP: {
String high = Utility.formatTemperature(
cursor.getDouble(cursor.getColumnIndex(WeatherEntry.COLUMN_MAX_TEMP)), isMetric);
((TextView) view).setText(high);
return true;
}
case COL_WEATHER_MIN_TEMP: {
// we have to do some formatting and possibly a conversion
String low = Utility.formatTemperature(
cursor.getDouble(cursor.getColumnIndex(WeatherEntry.COLUMN_MIN_TEMP)), isMetric);
((TextView) view).setText(low);
return true;
}
case COL_WEATHER_DATE: {
String dateString = Utility.formatDate(
cursor.getString(cursor.getColumnIndex(WeatherEntry.COLUMN_DATETEXT)));
((TextView) view).setText(dateString);
return true;
}
}
return false;
}
});
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
// Get a reference to the ListView, and attach this adapter to it.
ListView listView = (ListView) rootView.findViewById(R.id.listview_forecast);
listView.setAdapter(mForecastAdapter);
listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> adapterView, View view, int position, long l) {
Cursor cursor = mForecastAdapter.getCursor();
if (cursor != null && cursor.moveToPosition(position)) {
Intent intent = new Intent(getActivity(), DetailActivity.class)
.putExtra(DetailActivity.DATE_KEY, cursor.getString(COL_WEATHER_DATE));
startActivity(intent);
}
}
});
return rootView;
}
@Override
public void onActivityCreated(Bundle savedInstanceState) {
getLoaderManager().initLoader(FORECAST_LOADER, null, this);
super.onActivityCreated(savedInstanceState);
}
private void updateWeather() {
String location = Utility.getPreferredLocation(getActivity());
// update weather only if location is not an EMPTY string
if (location != null
&& location.length() > 0) {
new FetchWeatherTask(getActivity()).execute(location, SettingsActivity.FORECAST_DAYS);
}
}
@Override
public void onResume() {
super.onResume();
if (mLocation != null && !mLocation.equals(Utility.getPreferredLocation(getActivity()))) {
getLoaderManager().restartLoader(FORECAST_LOADER, null, this);
}
}
@Override
public Loader<Cursor> onCreateLoader(int id, Bundle args) {
// This is called when a new Loader needs to be created. This
// fragment only uses one loader, so we don't care about checking the id.
// To only show current and future dates, get the String representation for today,
// and filter the query to return weather only for dates after or including today.
// Only return data after today.
String startDate = WeatherContract.getDbDateString(new Date());
// Sort order: Ascending, by date.
String sortOrder = WeatherEntry.COLUMN_DATETEXT + " ASC";
mLocation = Utility.getPreferredLocation(getActivity());
if (mLocation == null || mLocation.length() == 0) {
mLocation = "00000";
}
Uri weatherForLocationUri = WeatherContract.WeatherEntry.buildWeatherLocationWithStartDate(mLocation, startDate);
Log.d(getString(R.string.app_name), weatherForLocationUri.toString());
// Now create and return a CursorLoader that will take care of
// creating a Cursor for the data being displayed.
return new CursorLoader(
getActivity(),
weatherForLocationUri,
FORECAST_COLUMNS,
null,
null,
sortOrder
);
}
@Override
public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
mForecastAdapter.swapCursor(data);
}
@Override
public void onLoaderReset(Loader<Cursor> loader) {
mForecastAdapter.swapCursor(null);
}
}
实用程序
public class Utility {
public static String getPreferredLocation(Context context) {
SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(context);
return prefs.getString(context.getString(R.string.pref_location_key),
context.getString(R.string.pref_location_default));
}
public static boolean isMetric(Context context) {
SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(context);
return prefs.getString(context.getString(R.string.pref_units_key),
context.getString(R.string.pref_units_metric))
.equals(context.getString(R.string.pref_units_metric));
}
static String formatTemperature(double temperature, boolean isMetric) {
double temp;
if ( !isMetric ) {
temp = 9*temperature/5+32;
} else {
temp = temperature;
}
return String.format("%.0f", temp);
}
static String formatDate(String dateString) {
Date date = WeatherContract.getDateFromDb(dateString);
return DateFormat.getDateInstance().format(date);
}
}
我已将 logcat 放入两个文件（Utility 和 ForecastFragment）中以演示该问题。这是 logcat 首次加载 ForecastFragment onCreateView 时，安装应用程序时。
07-05 17:35:57.562 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:35:57.563 21604-21604/com.example.android.weather.app D/JIGAR: isMetric true
这是 logcat 当 ForecastFragment onCreateView 加载时，按下刷新按钮后。
07-05 17:36:44.433 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.435 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.435 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.436 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.445 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.449 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.450 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.452 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.458 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.458 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.458 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.458 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.459 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.460 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.460 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.460 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.461 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.461 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.461 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.461 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.462 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.462 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.462 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.463 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.463 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.464 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.464 21604-21604/com.example.android.weather.app D/JIGAR: {}
07-05 17:36:44.464 21604-21604/com.example.android.weather.app D/JIGAR: {}
我现在已经从以上两个位置删除了 Log.d 语句，但非常欢迎您放置日志语句。
注意：这是一个家庭作业应用程序，文件中显示了 TO DO 及其完整的应用程序，但在玩应用程序和理解代码时，我在应用程序中发现了这个错误并试图理解它发生的原因。这是作业或任何提交的 NOT 部分。
你的sharedPreferences为空的原因是你一开始没有成功输入任何东西。
我建议以这种方式使用 sharedPreferences，因为这对我有用：
import android.content.SharedPreferences;
在你的函数中：
SharedPreferences preferences = getApplicationContext().getSharedPreferences("AppPref", MODE_PRIVATE);
SharedPreferences.Editor editor = preferences.edit();
editor.putString("**Input your data here**", **tag your data/give it a name*);//example editor.putString("userPassword", password);
editor.commit();//this one places your string into the sharedpreferences instance you created
为了在创建时访问您的共享首选项：
private String data; //this receives your data from sharedpref
@Override
protected void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
SharedPreferences conn = getSharedPreferences("AppPref", MODE_PRIVATE);
data = conn.getString("**your data tag**","");
}
希望这对您有所帮助。如果您希望存储会话中的值，则需要专门为运行时输入的数据创建一个 sharedpreferences 实例。我不太擅长技术解释，所以如果您有任何疑问，请要求澄清。
感谢 Dennis 和 Kaze，我的 android 应用程序正在 SettingActivity extends PreferenceActivity 中的 addPreferencesFromResource(R.xml.pref_general) 帮助下从 xml 文件加载默认共享首选项activity 当有人点击“设置”按钮时它会启动，因此在按下“设置”按钮之前不会填充共享首选项。
你关于填充默认首选项的问题让我研究了它是如何填充的，它应该使用 PreferenceManager.setDefaultValues 在 ForecastFragment onCreate 中填充，如下所示......
PreferenceManager.setDefaultValues(context, R.xml.pref_general, false);
这解决了我的问题。我会给你的答案投票！谢谢
您应该使用 PreferenceManager 中的以下方法从 xml 加载默认值（正如您在评论中所述，默认值是从 xml 加载的）。
static void setDefaultValues(Context context, int resId, boolean readAgain)
Sets the default values from an XML preference file by reading the values defined by each Preference item's android:defaultValue attribute.