我使用了preferenceActivity的一个特殊实现，它允许使用标题并且与旧的Android版本兼容。我想要完成的是我希望在ListPreference时重置CheckBoxPreference的值未选中，但只要调用setValue()或setEntries()，我就会获得null pointer Exception。这是我的代码：
import java.util.List;
import android.annotation.SuppressLint;
import android.content.Intent;
import android.content.SharedPreferences;
import android.content.SharedPreferences.OnSharedPreferenceChangeListener;
import android.os.Build;
import android.os.Bundle;
import android.preference.CheckBoxPreference;
import android.preference.ListPreference;
import android.preference.PreferenceManager;
import android.util.Log;
import com.actionbarsherlock.app.SherlockPreferenceActivity;
public class FragmentPreferences extends SherlockPreferenceActivity implements
OnSharedPreferenceChangeListener {
private static final String TAG = "FragmentPreferences";
private boolean themeIsDirty = false;
private ListPreference prefDspProfile;
@SuppressLint("NewApi")
@SuppressWarnings("deprecation")
@Override
protected void onCreate(Bundle savedInstanceState) {
setTheme(ActivityOriginal.THEME);
super.onCreate(savedInstanceState);
// Load the preferences from an XML resource
if (Build.VERSION.SDK_INT < Build.VERSION_CODES.HONEYCOMB) {
addPreferencesFromResource(R.xml.preference_general);
addPreferencesFromResource(R.xml.preference_layout);
addPreferencesFromResource(R.xml.preference_audio);
addPreferencesFromResource(R.xml.preference_dsp);
addPreferencesFromResource(R.xml.preference_error);
}
// turn off unaccessible dsp effects based on android version
if (Build.VERSION.SDK_INT > Build.VERSION_CODES.ICE_CREAM_SANDWICH_MR1) {
if (!android.media.audiofx.AcousticEchoCanceler.isAvailable()) {
setEchoCancelerAsIncompatible();
}
if (!android.media.audiofx.NoiseSuppressor.isAvailable()) {
setNoiseSuppressorAsIncompatible();
}
if (!android.media.audiofx.AutomaticGainControl.isAvailable()) {
setGainControlAsIncompatible();
}
} else {
setEchoCancelerAsIncompatible();
setNoiseSuppressorAsIncompatible();
setGainControlAsIncompatible();
}
}
private void setGainControlAsIncompatible() {
CheckBoxPreference prefDspAutomaticGainControl = (CheckBoxPreference) getPreferenceScreen()
.findPreference("pref_dsp_automatic_gain_control");
prefDspAutomaticGainControl.setChecked(false);
prefDspAutomaticGainControl
.setSummaryOff(R.string.pref_dsp_automatic_gain_control_incompatible);
prefDspAutomaticGainControl.setEnabled(false);
}
private void setNoiseSuppressorAsIncompatible() {
CheckBoxPreference prefDspNoiseSuppressor = (CheckBoxPreference) getPreferenceScreen()
.findPreference("pref_dsp_noise_suppressor");
prefDspNoiseSuppressor.setChecked(false);
prefDspNoiseSuppressor
.setSummaryOff(R.string.pref_dsp_noise_suppressor_incompatible);
prefDspNoiseSuppressor.setEnabled(false);
}
private void setEchoCancelerAsIncompatible() {
CheckBoxPreference prefDspEchoCanceler = (CheckBoxPreference) getPreferenceScreen()
.findPreference("pref_dsp_echo_canceler");
prefDspEchoCanceler.setChecked(false);
prefDspEchoCanceler
.setSummaryOff(R.string.pref_dsp_echo_canceler_incompatible);
prefDspEchoCanceler.setEnabled(false);
}
@SuppressLint("NewApi")
@Override
public void onBuildHeaders(List<Header> target) {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
loadHeadersFromResource(R.xml.preference_headers, target);
for (Header header : target) {
switch (header.titleRes) {
case R.string.prefs_header1_title:
header.iconRes = ActivityOriginal.getIcon(
getSupportActionBar().getThemedContext(),
"ic_menu_pref_general");
break;
case R.string.prefs_header2_title:
header.iconRes = ActivityOriginal.getIcon(
getApplicationContext(), "ic_menu_pref_layout");
break;
case R.string.prefs_header3_title:
header.iconRes = ActivityOriginal.getIcon(
getApplicationContext(), "ic_menu_pref_sound");
break;
case R.string.prefs_header4_title:
header.iconRes = ActivityOriginal.getIcon(
getApplicationContext(), "ic_menu_pref_error");
break;
case R.string.prefs_header5_title:
header.iconRes = ActivityOriginal.getIcon(
getApplicationContext(), "ic_menu_pref_dsp");
break;
}
}
}
}
@Override
public void onStop() {
/*
* Toast.makeText(this.getApplicationContext(),
* getString(R.string.reset_to_make_changes), Toast.LENGTH_LONG).show();
*/
super.onStop();
}
@Override
public void onSharedPreferenceChanged(SharedPreferences sharedPreferences,
String key) {
Log.i(TAG, "changed key is : " + key);
SharedPreferences prefs = PreferenceManager
.getDefaultSharedPreferences(this);
if ("pref_dsp_bass_boost".equals(key)
|| "pref_dsp_low_pass_filter".equals(key)) {
initPrefsDsp();
if (prefs.getBoolean("pref_dsp_bass_boost", true)
&& prefs.getBoolean("pref_dsp_low_pass_filter", true)) {
prefDspProfile.setValue("0");
prefDspProfile = null;
Log.i(TAG, "set the pref_dsp_profile to 0 ");
} else {
prefDspProfile.setValue("1");
prefDspProfile = null;
Log.i(TAG, "set the pref_dsp_profile to 1 ");
}
}
if ("pref_dsp_profile".equals(key)) {
initPrefsDsp();
if ("0".equals(prefDspProfile.getValue())) {
CheckBoxPreference prefDspBassBoost = (CheckBoxPreference) findPreference("pref_dsp_low_pass_filter");
prefDspBassBoost.setChecked(true);
CheckBoxPreference prefDspLowPassFilter = (CheckBoxPreference) findPreference("pref_dsp_bass_boost");
prefDspLowPassFilter.setChecked(true);
}
}
if ("theme_preference".equals(key)) {
Log.i(this.getClass().getName(), "themeIsDirty");
themeIsDirty = true;
Intent in = new Intent();
in.putExtra("themeIsDirty", themeIsDirty);
setResult(RESULT_OK, in);
PreferenceManager.getDefaultSharedPreferences(this)
.unregisterOnSharedPreferenceChangeListener(this);
}
}
private void initPrefsDsp() {
/*
* CharSequence[] dspEntries = getResources().getStringArray(
* R.array.prefs_dsp_entries); CharSequence[] dspValues =
* getResources().getStringArray( R.array.prefs_dsp_values);
*/
CharSequence[] dspEntries = { "Dark grey", "Light grey" };
CharSequence[] dspValues = { "0", "1" };
prefDspProfile = (ListPreference) findPreference("pref_dsp_profile");
if (prefDspProfile == null) {
Log.i(TAG, "prefDspProfile is null");
return;
}
prefDspProfile.setEntries(dspEntries);
prefDspProfile.setEntryValues(dspValues);
}
@Override
protected void onResume() {
super.onResume();
PreferenceManager.getDefaultSharedPreferences(this)
.registerOnSharedPreferenceChangeListener(this);
/*
* getPreferenceScreen().getSharedPreferences()
* .registerOnSharedPreferenceChangeListener(this);
*/
}
@Override
public void onBackPressed() {
// the following block will warn user after back button is pressed
PreferenceManager.getDefaultSharedPreferences(this)
.unregisterOnSharedPreferenceChangeListener(this);
/*
* getPreferenceScreen().getSharedPreferences()
* .unregisterOnSharedPreferenceChangeListener(this);
*/
Intent in = new Intent();
in.putExtra("themeIsDirty", themeIsDirty);
setResult(RESULT_OK, in);
super.onBackPressed();
}
@Override
protected void onPause() {
super.onPause();
}
}
preference_dsp.xml
<?xml version="1.0" encoding="utf-8"?>
<ListPreference
android:defaultValue="0"
android:dialogTitle="@string/pref_dsp_title_dialog"
android:entries="@array/prefs_dsp_entries"
android:entryValues="@array/prefs_dsp_values"
android:key="pref_dsp_profile"
android:summary="@string/pref_dsp_summary"
android:title="@string/pref_dsp_title" />
<CheckBoxPreference
android:defaultValue="true"
android:key="pref_dsp_low_pass_filter"
android:summaryOff="@string/pref_dsp_low_pass_filter_disabled"
android:summaryOn="@string/pref_dsp_low_pass_filter_enabled"
android:title="@string/pref_dsp_low_pass_filter_title" />
<CheckBoxPreference
android:defaultValue="true"
android:key="pref_dsp_bass_boost"
android:summaryOff="@string/pref_dsp_bass_boost_disabled"
android:summaryOn="@string/pref_dsp_bass_boost_enabled"
android:title="@string/pref_dsp_bass_boost_title" />
<CheckBoxPreference
android:defaultValue="true"
android:key="pref_dsp_echo_canceler"
android:summaryOff="@string/pref_dsp_echo_canceler_disabled"
android:summaryOn="@string/pref_dsp_echo_canceler_enabled"
android:title="@string/pref_dsp_echo_canceler_title" />
<CheckBoxPreference
android:defaultValue="true"
android:key="pref_dsp_noise_suppressor"
android:summaryOff="@string/pref_dsp_noise_suppressor_disabled"
android:summaryOn="@string/pref_dsp_noise_suppressor_enabled"
android:title="@string/pref_dsp_noise_suppressor_title" />
<CheckBoxPreference
android:defaultValue="false"
android:key="pref_dsp_automatic_gain_control"
android:summaryOff="@string/pref_dsp_automatic_gain_control_disabled"
android:summaryOn="@string/pref_dsp_automatic_gain_control_enabled"
android:title="@string/pref_dsp_automatic_gain_control_title" />
<ListPreference
android:defaultValue="2.0f"
android:dialogTitle="@string/prefs_dsp_sound_gain_dialog_title"
android:entries="@array/prefs_dsp_sound_gain_entries"
android:entryValues="@array/prefs_dsp_sound_gain_values"
android:key="prefs_dsp_sound_gain"
android:summary="@string/prefs_dsp_sound_gain_summary"
android:title="@string/prefs_dsp_sound_gain_title" />
我无法在网上找到关于如何动态修改preference值的完整示例。
答案 0 :(得分：4)
尝试（例如布尔值）：
SharedPreferences.Editor prefs = PreferenceManager.getDefaultSharedPreferences(this).edit();
prefs.putBoolean("your_pref", false);
prefs.commit();
答案 1 :(得分：1)
findPreference("pref_dsp_profile")正在返回null。基于您目前共享的代码不明显的原因，没有名为pref_dsp_profile的首选项可访问。也许你的情况不成立（Build.VERSION.SDK_INT < Build.VERSION_CODES.HONEYCOMB），或者这些偏好不在这些文件中。