不要将此标记为重复，因为我在互联网上找不到任何有用的内容。
我已在我的Android应用中实现了首选项屏幕。我想在用户点击编辑文本首选项时添加一个功能，如果他填充该字段 ＆＃34; CONFIRM＆＃34; 然后应用程序的数据库将被清空，但我不知道如何从对话框中捕获用户输入。
到目前为止我有什么
if (preference instanceof EditTextPreference) {
if (preference.getKey().matches("pref_reset_savings")){
if(((EditTextPreference) preference).getText().matches("CONFIRM")){
Log.i("reset", "confirmed");
}
}
}
给我一个NullPointerException
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.musa.mymoneybox/activities.Settings}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.preference.Preference.setOnPreferenceChangeListener(android.preference.Preference$OnPreferenceChangeListener)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2817)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593)
at android.os.Handler.dispatchMessage(Handler.java:105)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6541)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.preference.Preference.setOnPreferenceChangeListener(android.preference.Preference$OnPreferenceChangeListener)' on a null object reference
at activities.Settings.bindPreferenceSummaryToValue(Settings.java:49)
at activities.Settings.access$000(Settings.java:14)
at activities.Settings$PrefFragment.onCreate(Settings.java:40)
at android.app.Fragment.performCreate(Fragment.java:2593)
at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1234)
at android.app.FragmentManagerImpl.addAddedFragments(FragmentManager.java:2415)
at android.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2194)
at android.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManager.java:2148)
at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:2049)
at android.app.FragmentManagerImpl.dispatchMoveToState(FragmentManager.java:3044)
at android.app.FragmentManagerImpl.dispatchActivityCreated(FragmentManager.java:2991)
at android.app.FragmentController.dispatchActivityCreated(FragmentController.java:178)
at android.app.Activity.performCreateCommon(Activity.java:6969)
at android.app.Activity.performCreate(Activity.java:6977)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1213)
我的设置活动全码
package activities;
import android.os.Bundle;
import android.preference.EditTextPreference;
import android.preference.Preference;
import android.preference.PreferenceFragment;
import android.preference.PreferenceManager;
import android.util.Log;
import com.musa.mymoneybox.R;
import configs.AppCompatPreferenceActivity;
public class Settings extends AppCompatPreferenceActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
android.support.v7.app.ActionBar actionBar = getSupportActionBar();
actionBar.setDisplayHomeAsUpEnabled(true);
this.runOnUiThread(new Runnable() {
public void run() {
//Load Settings Fragment
getFragmentManager().beginTransaction().replace(android.R.id.content, new PrefFragment()).commit();
}});
}
public static class PrefFragment extends PreferenceFragment {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
addPreferencesFromResource(R.xml.pref_main);
bindPreferenceSummaryToValue(findPreference("pref_sound"));
bindPreferenceSummaryToValue(findPreference("pref_notifications"));
}
}
private static void bindPreferenceSummaryToValue(Preference preference) {
preference.setOnPreferenceChangeListener(sBindPreferenceSummaryToValueListener);
sBindPreferenceSummaryToValueListener.onPreferenceChange(preference,
PreferenceManager
.getDefaultSharedPreferences(preference.getContext())
.getBoolean(preference.getKey(), true));
}
private static Preference.OnPreferenceChangeListener sBindPreferenceSummaryToValueListener = new Preference.OnPreferenceChangeListener() {
@Override
public boolean onPreferenceChange(Preference preference, Object newValue) {
if (newValue instanceof Boolean) {
boolean isChecked = (boolean) newValue;
if(preference.getKey().matches("pref_notifications")){
if (isChecked){
Log.i("Notifications", "True");
} else {
Log.i("Notifications", "False");
}
}
if (preference instanceof EditTextPreference) {
if (preference.getKey().matches("pref_reset_savings")){
if(((EditTextPreference) preference).getText().matches("CONFIRM")){
Log.i("reset", "confirmed");
}
}
}
}
return true;
}
};
}
我们将非常感谢任何帮助！
答案 0 :(得分：1)
在使用之前尝试将preference投射到EditTextPreference：
if (preference instanceof EditTextPreference) {
EditTextPreference newPreference = (EditTextPreference) preference;
if (newPreference.getKey().matches("pref_reset_savings")){
if(newPreference.getText().matches("CONFIRM")){
Log.i("reset", "confirmed");
}
}
}
希望它有所帮助。
答案 1 :(得分：0)
您在设置首选项的侦听器时收到NullPointerException，这意味着您的首选项为null。如果您的首选项键与findPreference()方法中的参数匹配，请检查首选项XML。
在您的监听器中，您在首选项上调用getText()，可能会返回null，因为您输入的值尚未存储在首选项中。顺便说一下，当您不使用正则表达式来比较字符串时，可以使用equals()代替matches()。
if (newValue.equals("CONFIRM")){
Log.i("reset", "confirmed");
}