Question

我有一个非常不完整的android项目，其中设置选项有一个列表首选项。我想要做的是 - 从列表中永久隐藏字符黑名单选项，但它将在内部工作。为此，我做了

<EditTextPreference android:key="preference_character_blacklist"
        android:title="Character blacklist"
        android:visibility="gone"/>

但它不起作用。相反，当我在运行项目后进入设置时显示错误。设置看起来像this-file：///home/Piyal/Desktop/Screenshot.png 我的preference.xml是 -

<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">

<!-- GENERAL SETTINGS -->
<PreferenceCategory android:title="General settings">

    <CheckBoxPreference android:key="preference_capture_continuous"
        android:title="Continuous preview"
        android:entries="@array/capturemodes" />

    <ListPreference android:title="Recognize"
        android:key="sourceLanguageCodeOcrPref"
        android:entries="@array/languagenames"
        android:entryValues="@array/iso6393" />

</PreferenceCategory>

<!-- TRANSLATION SETTINGS -->
<PreferenceCategory android:title="Translation settings"
                    >

    <CheckBoxPreference android:key="preference_translation_toggle_translation"
        android:title="Translate"/>

    <ListPreference android:key="targetLanguageCodeTranslationPref"  
        android:title="Translate to"
        android:dependency="preference_translation_toggle_translation"
        android:entries="@array/translationtargetlanguagenames_google" 
        android:entryValues="@array/translationtargetiso6391_google" />

    <ListPreference android:key="preference_translator" 
        android:title="Translator"
        android:dependency="preference_translation_toggle_translation"
        android:entries="@array/translators" 
        android:entryValues="@array/translators"

         />


</PreferenceCategory>

<!-- ADVANCED SETTINGS -->
<PreferenceCategory android:title="Advanced settings">

    <ListPreference android:key="preference_ocr_engine_mode"
        android:title="OCR engine"
        android:entries="@array/ocrenginemodes"
        android:entryValues="@array/ocrenginemodes"/>

    <ListPreference android:key="preference_operator_mode"
        android:title="Operator"
        android:entries="@array/operatormodes"
        android:entryValues="@array/operatormodes"
        />

    <CheckBoxPreference
        android:key="preferences_auto_focus"
        android:title="Autofocus"/>

    <CheckBoxPreference
        android:key="preferences_play_beep"
        android:title="Beep"/>

    <EditTextPreference android:key="preference_character_blacklist"
        android:title="Character blacklist"/>

    <EditTextPreference

        android:key="preference_character_whitelist"
        android:title="Character whitelist"

        />


 <!-- 
    <CheckBoxPreference
        android:key="preference_toggle_light"
        android:title="Light"/>
-->

    <ListPreference android:key="preference_page_segmentation_mode"
        android:title="Page segmentation"
        android:entries="@array/pagesegmentationmodes"
        android:entryValues="@array/pagesegmentationmodes" />

    <CheckBoxPreference
        android:key="preferences_reverse_image"
        android:title="Reversed camera image"
        android:summary="(For devices with only a front camera)"/>

</PreferenceCategory>

  </PreferenceScreen>`

这是我的偏好 -

    public class PreferencesActivity extends PreferenceActivity implements
  OnSharedPreferenceChangeListener {

  // Preference keys not carried over from R.M Theis project project
  public static final String KEY_OPERATOR_MODE = "preference_operator_mode";


  // Preference keys not carried over from ZXing project
  public static final String KEY_SOURCE_LANGUAGE_PREFERENCE = 

  "sourceLanguageCodeOcrPref";
  public static final String KEY_TARGET_LANGUAGE_PREFERENCE =  

"targetLanguageCodeTranslationPref";
  public static final String KEY_TOGGLE_TRANSLATION = 

"preference_translation_toggle_translation";
  public static final String KEY_CONTINUOUS_PREVIEW = 

"preference_capture_continuous";
  public static final String KEY_PAGE_SEGMENTATION_MODE = 

"preference_page_segmentation_mode";
  public static final String KEY_OCR_ENGINE_MODE = "preference_ocr_engine_mode";
  public static final String KEY_CHARACTER_BLACKLIST = 

"preference_character_blacklist";
  public static final String KEY_CHARACTER_WHITELIST = 

"preference_character_whitelist";
  public static final String KEY_TOGGLE_LIGHT = "preference_toggle_light";
  public static final String KEY_TRANSLATOR = "preference_translator";

  // Preference keys carried over from ZXing project
  public static final String KEY_AUTO_FOCUS = "preferences_auto_focus";
  public static final String KEY_HELP_VERSION_SHOWN = 

"preferences_help_version_shown";
  public static final String KEY_NOT_OUR_RESULTS_SHOWN = 

"preferences_not_our_results_shown";
  public static final String KEY_REVERSE_IMAGE = "preferences_reverse_image";
  public static final String KEY_PLAY_BEEP = "preferences_play_beep";
  public static final String KEY_VIBRATE = "preferences_vibrate";

  public static final String TRANSLATOR_BING = "Bing Translator";
  public static final String TRANSLATOR_GOOGLE = "Google Translate";

  //private CheckBoxPreference checkBoxPreferenceContinuousPreview;
  private ListPreference listPreferenceSourceLanguage;
  //private CheckBoxPreference checkBoxTranslate;
  private ListPreference listPreferenceTargetLanguage;  
  private ListPreference listPreferenceTranslator;
  private ListPreference listPreferenceOcrEngineMode;
  //private CheckBoxPreference checkBoxBeep;
  private EditTextPreference editTextPreferenceCharacterBlacklist;
  private EditTextPreference editTextPreferenceCharacterWhitelist;
  private ListPreference listPreferencePageSegmentationMode;
  //private CheckBoxPreference checkBoxReversedImage;

  private ListPreference listPreferenceOperatorMode;

  private static SharedPreferences sharedPreferences;

  /**
   * Set the default preference values.
   * 
   * @param Bundle
   *            savedInstanceState the current Activity's state, as passed by
   *            Android
   */
  @Override
  protected void onCreate(Bundle savedInstanceState) 
  {
    super.onCreate(savedInstanceState);
    getWindow().setBackgroundDrawableResource(R.drawable.background_holo_dark);
    addPreferencesFromResource(R.xml.preferences);

    sharedPreferences = PreferenceManager.getDefaultSharedPreferences(this);

    //checkBoxPreferenceContinuousPreview = (CheckBoxPreference) 

getPreferenceScreen().findPreference(KEY_CONTINUOUS_PREVIEW);
    listPreferenceSourceLanguage = (ListPreference) 

getPreferenceScreen().findPreference(KEY_SOURCE_LANGUAGE_PREFERENCE);
    //checkBoxTranslate = (CheckBoxPreference) 

getPreferenceScreen().findPreference(KEY_TOGGLE_TRANSLATION);
    listPreferenceTargetLanguage = (ListPreference) 

getPreferenceScreen().findPreference(KEY_TARGET_LANGUAGE_PREFERENCE);
    listPreferenceTranslator = (ListPreference) 

getPreferenceScreen().findPreference(KEY_TRANSLATOR);    
    listPreferenceOcrEngineMode = (ListPreference) 

getPreferenceScreen().findPreference(KEY_OCR_ENGINE_MODE);
    listPreferenceOperatorMode = (ListPreference)  

getPreferenceScreen().findPreference(KEY_OPERATOR_MODE);

    //checkBoxBeep = (CheckBoxPreference) 

getPreferenceScreen().findPreference(KEY_PLAY_BEEP);
    editTextPreferenceCharacterBlacklist = (EditTextPreference) 
getPreferenceScreen().findPreference(KEY_CHARACTER_BLACKLIST);
    editTextPreferenceCharacterWhitelist = (EditTextPreference) 
getPreferenceScreen().findPreference(KEY_CHARACTER_WHITELIST);
    listPreferencePageSegmentationMode = (ListPreference) 
getPreferenceScreen().findPreference(KEY_PAGE_SEGMENTATION_MODE);
    //checkBoxReversedImage = (CheckBoxPreference) 
getPreferenceScreen().findPreference(KEY_REVERSE_IMAGE);

    // Create the entries/entryvalues for the translation target language list.
    initTranslationTargetList();

  }

  /**
   * Interface definition for a callback to be invoked when a shared
   * preference is changed. Sets summary text for the app's preferences. Summary  
text values show the
   * current settings for the values.
   * 
   * @param sharedPreferences
   *            the Android.content.SharedPreferences that received the change
   * @param key
   *            the key of the preference that was changed, added, or removed
   */
  @Override
  public void onSharedPreferenceChanged(SharedPreferences sharedPreferences,
      String key) {    
    // Update preference summary values to show current preferences
    if (key.equals(KEY_TRANSLATOR)) {
      listPreferenceTranslator.setSummary(sharedPreferences.getString(key, 
CaptureActivity.DEFAULT_TRANSLATOR));
    } else if(key.equals(KEY_SOURCE_LANGUAGE_PREFERENCE)) {

      // Set the summary text for the source language name

  listPreferenceSourceLanguage.
setSummary(LanguageCodeHelper.getOcrLanguageName(getBaseContext(),  
sharedPreferences.getString(key,         
CaptureActivity.DEFAULT_SOURCE_LANGUAGE_CODE)));

      // Retrieve the character blacklist/whitelist for the new language
      String blacklist = OcrCharacterHelper.getBlacklist(sharedPreferences, 
listPreferenceSourceLanguage.getValue());
      String whitelist = OcrCharacterHelper.getWhitelist(sharedPreferences, 
listPreferenceSourceLanguage.getValue());

      // Save the character blacklist/whitelist to preferences
      sharedPreferences.edit().putString(KEY_CHARACTER_BLACKLIST, 
blacklist).commit();
      sharedPreferences.edit().putString(KEY_CHARACTER_WHITELIST, 
whitelist).commit();

      // Set the blacklist/whitelist summary text
      editTextPreferenceCharacterBlacklist.setSummary(blacklist);
      editTextPreferenceCharacterWhitelist.setSummary(whitelist);

    } else if (key.equals(KEY_TARGET_LANGUAGE_PREFERENCE)) {

listPreferenceTargetLanguage.
setSummary(LanguageCodeHelper.getTranslationLanguageName(this,  
sharedPreferences.getString(key,        
CaptureActivity.DEFAULT_TARGET_LANGUAGE_CODE)));
        } else if (key.equals(KEY_PAGE_SEGMENTATION_MODE)) {

listPreferencePageSegmentationMode.setSummary(sharedPreferences.getString(key,  
CaptureActivity.DEFAULT_PAGE_SEGMENTATION_MODE));
    } else if (key.equals(KEY_OCR_ENGINE_MODE)) {
      listPreferenceOcrEngineMode.setSummary(sharedPreferences.getString(key,  
CaptureActivity.DEFAULT_OCR_ENGINE_MODE));
    }
    else if (key.equals(KEY_OPERATOR_MODE))
    {
        listPreferenceOperatorMode.setSummary(sharedPreferences.getString(key, 
CaptureActivity.DEFAULT_OPERATOR_MODE));
    }  
    else if (key.equals(KEY_CHARACTER_BLACKLIST)) {  

      // Save a separate, language-specific character blacklist for this language
      OcrCharacterHelper.setBlacklist(sharedPreferences, 
          listPreferenceSourceLanguage.getValue(), 
          sharedPreferences.getString(key, 
OcrCharacterHelper.getDefaultBlacklist(listPreferenceSourceLanguage.getValue())));

      // Set the summary text
    editTextPreferenceCharacterBlacklist.
setSummary(sharedPreferences.getString(key, 
OcrCharacterHelper.getDefaultBlacklist(listPreferenceSourceLanguage.getValue())));

    } else if (key.equals(KEY_CHARACTER_WHITELIST)) {

      // Save a separate, language-specific character blacklist for this language
      OcrCharacterHelper.setWhitelist(sharedPreferences, 
          listPreferenceSourceLanguage.getValue(), 
          sharedPreferences.getString(key, 
OcrCharacterHelper.getDefaultWhitelist(listPreferenceSourceLanguage.getValue())));

      // Set the summary text
      editTextPreferenceCharacterWhitelist.
setSummary(sharedPreferences.getString(key, 
OcrCharacterHelper.getDefaultWhitelist  
(listPreferenceSourceLanguage.getValue())));

    }

    // Update the languages available for translation based on the current 
translator selected.
    if (key.equals(KEY_TRANSLATOR)) {
      initTranslationTargetList();
    }

  }

  /**
   * Sets the list of available languages and the current target language for 
translation. Called
   * when the key for the current translator is changed.
   */
  void initTranslationTargetList() {
    // Set the preference for the target language code, in case we've just 
switched from Google
    // to Bing, or Bing to Google.
    String currentLanguageCode = 
sharedPreferences.getString(KEY_TARGET_LANGUAGE_PREFERENCE, 
        CaptureActivity.DEFAULT_TARGET_LANGUAGE_CODE);

    // Get the name of our language
    String currentLanguage = 
LanguageCodeHelper.getTranslationLanguageName(getBaseContext(), 
        currentLanguageCode);
    String[] translators = getResources().getStringArray(R.array.translators);
    String translator = sharedPreferences.getString(KEY_TRANSLATOR, 
CaptureActivity.DEFAULT_TRANSLATOR);
    String newLanguageCode = "";
    if (translator.equals(translators[0])) { // Bing
      // Update the list of available languages for the currently-chosen 
translation API.

listPreferenceTargetLanguage.
setEntries(R.array.translationtargetlanguagenames_microsoft);
      listPreferenceTargetLanguage.
setEntryValues(R.array.translationtargetiso6391_microsoft);

      // Get the corresponding code for our language name
      newLanguageCode = TranslatorBing.toLanguage(currentLanguage);
    } else if (translator.equals(translators[1])) { // Google
      // Update the list of available languages for the currently-chosen 
translation API.
      listPreferenceTargetLanguage.
setEntries(R.array.translationtargetlanguagenames_google);
      listPreferenceTargetLanguage.
setEntryValues(R.array.translationtargetiso6391_google);

      // Get the corresponding code for our language name      
      newLanguageCode = TranslatorGoogle.toLanguage(currentLanguage);
    }

    // Store the code as the target language preference
    String newLanguageName = LanguageCodeHelper.
getTranslationLanguageName(getBaseContext(),
        newLanguageCode);
    listPreferenceTargetLanguage.
setValue(newLanguageName); // Set the radio button in the list

sharedPreferences.edit().putString(PreferencesActivity.KEY_TARGET_LANGUAGE_PREFERENCE, 
        newLanguageCode).commit();
    listPreferenceTargetLanguage.setSummary(newLanguageName);
  }

  /**
   * Sets up initial preference summary text
   * values and registers the OnSharedPreferenceChangeListener.
   */
  @Override
  protected void onResume() {
    super.onResume();
    // Set up the initial summary values
    listPreferenceTranslator.
setSummary(sharedPreferences.getString(KEY_TRANSLATOR, 
CaptureActivity.DEFAULT_TRANSLATOR));
    listPreferenceSourceLanguage.
setSummary(LanguageCodeHelper.getOcrLanguageName(getBaseContext(), 
sharedPreferences.getString     
(KEY_SOURCE_LANGUAGE_PREFERENCE, CaptureActivity.DEFAULT_SOURCE_LANGUAGE_CODE)));
    listPreferenceTargetLanguage.
setSummary(LanguageCodeHelper.getTranslationLanguageName(getBaseContext(), 
sharedPreferences.getString 
(KEY_TARGET_LANGUAGE_PREFERENCE, CaptureActivity.DEFAULT_TARGET_LANGUAGE_CODE)));
    listPreferencePageSegmentationMode.
setSummary(sharedPreferences.getString(KEY_PAGE_SEGMENTATION_MODE,
    CaptureActivity.DEFAULT_PAGE_SEGMENTATION_MODE));
    listPreferenceOcrEngineMode.
setSummary(sharedPreferences.getString(KEY_OCR_ENGINE_MODE, 
CaptureActivity.DEFAULT_OCR_ENGINE_MODE));
    listPreferenceOperatorMode.
setSummary(sharedPreferences.getString(KEY_OPERATOR_MODE, 
CaptureActivity.DEFAULT_OPERATOR_MODE));
    editTextPreferenceCharacterBlacklist.
setSummary(sharedPreferences.getString(KEY_CHARACTER_BLACKLIST,     
OcrCharacterHelper.getDefaultBlacklist(listPreferenceSourceLanguage.getValue())));
   editTextPreferenceCharacterWhitelist.
setSummary(sharedPreferences.getString
(KEY_CHARACTER_WHITELIST,OcrCharacterHelper.getDefaultWhitelist 
(listPreferenceSourceLanguage.getValue())));

    // Set up a listener whenever a key changes
    getPreferenceScreen().
getSharedPreferences().registerOnSharedPreferenceChangeListener(this);
  }

  /**
   * Called when Activity is about to lose focus. Unregisters the
   * OnSharedPreferenceChangeListener.
   */
  @Override
  protected void onPause() {
    super.onPause();
    getPreferenceScreen().
getSharedPreferences().unregisterOnSharedPreferenceChangeListener(this);
  }
}

`

添加后的堆栈跟踪。getPreferenceScreen（）removePreference（editTextPreferenceCharacterBlacklist）;

在onCreate（）中

。

05-30 17:42:00.546: E/AndroidRuntime(379): FATAL EXCEPTION: main

05-30 17:42:00.546: E/AndroidRuntime(379): java.lang.RuntimeException: Unable to start 
activity  
ComponentInfo{automated.card.recharge.ocr/automated.card.
recharge.ocr.PreferencesActivity}: java.lang.NullPointerException
05-30 17:42:00.546: E/AndroidRuntime(379):  at 
android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)

05-30 17:42:00.546: E/AndroidRuntime(379):  at 
android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)

05-30 17:42:00.546: E/AndroidRuntime(379):  at 
android.app.ActivityThread.access$1500(ActivityThread.java:117)

05-30 17:42:00.546: E/AndroidRuntime(379):  at 
android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)

05-30 17:42:00.546: E/AndroidRuntime(379):  at 
android.os.Handler.dispatchMessage(Handler.java:99)

05-30 17:42:00.546: E/AndroidRuntime(379):  at android.os.Looper.loop(Looper.java:123)

05-30 17:42:00.546: E/AndroidRuntime(379):  at 
android.app.ActivityThread.main(ActivityThread.java:3683)

05-30 17:42:00.546: E/AndroidRuntime(379):  at 
java.lang.reflect.Method.invokeNative(Native Method)

05-30 17:42:00.546: E/AndroidRuntime(379):  at 
java.lang.reflect.Method.invoke(Method.java:507)

05-30 17:42:00.546: E/AndroidRuntime(379):  at 
com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)

05-30 17:42:00.546: E/AndroidRuntime(379):  at 
com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)

05-30 17:42:00.546: E/AndroidRuntime(379):  at dalvik.system.NativeStart.main(Native 
Method)

05-30 17:42:00.546: E/AndroidRuntime(379): Caused by: java.lang.NullPointerException

05-30 17:42:00.546: E/AndroidRuntime(379):  at 
android.preference.PreferenceGroup.removePreferenceInt(PreferenceGroup.java:181)

05-30 17:42:00.546: E/AndroidRuntime(379):  at 

android.preference.PreferenceGroup.removePreference(PreferenceGroup.java:174) 

05-30 17:42:00.546: E/AndroidRuntime(379):  at 
automated.card.recharge.ocr.PreferencesActivity.onCreate(PreferencesActivity.java:103)

05-30 17:42:00.546: E/AndroidRuntime(379):  at 
android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)

05-30 17:42:00.546: E/AndroidRuntime(379):  at 
android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)

05-30 17:42:00.546: E/AndroidRuntime(379):  at  
com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)

05-30 17:42:00.546: E/AndroidRuntime(379):  at dalvik.system.NativeStart.main(Native  
Method)

05-30 17:42:00.546: E/AndroidRuntime(379): Caused by: java.lang.NullPointerException

05-30 17:42:00.546: E/AndroidRuntime(379):  at 
android.preference.PreferenceGroup.removePreferenceInt(PreferenceGroup.java:181)

05-30 17:42:00.546: E/AndroidRuntime(379):  at 
android.preference.PreferenceGroup.removePreference(PreferenceGroup.java:174)

05-30 17:42:00.546: E/AndroidRuntime(379):  at 
automated.card.recharge.ocr.PreferencesActivity.onCreate(PreferencesActivity.java:103)

05-30 17:42:00.546: E/AndroidRuntime(379):  at 
android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)

05-30 17:42:00.546: E/AndroidRuntime(379):  at 
android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)

Answer 1

你应该可以删除：

<EditTextPreference android:key="preference_character_blacklist"
        android:title="Character blacklist"
        android:visibility="gone"/>

来自您的preferences.xml的

。这将阻止它出现在“设置”菜单中。

要使设置在内部工作，我建议您阅读SharedPreferences。 Android Storage Options Guide将说明如何使用SharedPreferences存储和检索设置值。

我修改了以下示例来存储上面链接的指南中的字符串：

public class Calc extends Activity {
    public static final String PREFS_NAME = "MyPrefsFile";

    @Override
    protected void onCreate(Bundle state){
       super.onCreate(state);
       . . .

       // Restore preferences
       SharedPreferences settings = getSharedPreferences(PREFS_NAME, 0);
       String silent = settings.getString("character_blacklist", "");
    }

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

      // We need an Editor object to make preference changes.
      // All objects are from android.context.Context
      SharedPreferences settings = getSharedPreferences(PREFS_NAME, 0);
      SharedPreferences.Editor editor = settings.edit();
      //Some test characters for the blacklist
      mBlackListChars = "a,g,t,h,f";
      editor.putString("character_blacklist", mBlackListChars);

      // Commit the edits
      editor.commit();
    }
}

请注意，您可能希望在onCreate()和onStop()之外调用这些方法，这纯粹是为了说明。另外，我会提请您注意SharedPreferences可以处理StringSet的事实，这可能对您存储多个字符有用。请参阅getStringSet()中的SharedPreferences方法。

<强>更新

为了保留首选项但只是将其隐藏起来，您可以以编程方式将其删除。看起来有点像黑客，但考虑将其添加到'PreferenceActivity'中的'OnCreate（）'

getPreferenceScreen().removePreference(editTextPreferenceCharacterBlacklist);

<强>更新

看起来您的问题是由editTextPreferenceCharacterBlacklist为空引起的。问题，因为在您运行我指定的行时，它尚未设置为您的实例变量。你可以尝试按如下方式找到它：

getPreferenceScreen().removePreference(getPreferenceScreen().findPreference(KEY_CHARACTER_BLACKLIST));

隐藏列表首选项中的选项

1 个答案: