当我使用findPreference(key)获取首选项的特定部分并动态添加值时,我得到的是null。
我不知道我在做什么错。我尝试了其他使用findPreference()方法的方法。我浏览了有关Stackoverflow的教程和问答,但都没有成功。
这是我的SettingsActivity代码:
public class SettingsActivity extends AppCompatActivity {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
FragmentManager fm = getSupportFragmentManager();
SettingsFragment sf = new SettingsFragment();
fm.beginTransaction()
.replace(R.id.content, sf)
.commit();
setContentView(R.layout.activity_settings);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
sf.addCustomList("pref_key_calendar", new CharSequence[]{"One", "Two", "Three"}, new CharSequence[]{ "1", "2", "3" });
}
public static class SettingsFragment extends PreferenceFragmentCompat {
@Override
public void onCreatePreferences(Bundle savedInstanceState, String rootkey) {
setPreferencesFromResource(R.xml.pref_settings, rootkey);
}
public void addCustomList(String key, CharSequence[] entries, CharSequence[] entryValues) {
ListPreference customListPref = (ListPreference) findPreference(key);
customListPref.setEntries(entries);
customListPref.setEntryValues(entryValues);
}
}
}
这是带有参考的XML:
<?xml version="1.0" encoding="utf-8"?>
<PreferenceScreen
xmlns:android="http://schemas.android.com/apk/res/android">
<PreferenceCategory
android:title="Main"
android:key="pref_key_settings_main">
<ListPreference
android:key="pref_key_calendar"
android:title="@string/pref_key_calendar"
android:summary="@string/pref_key_calendar_descr"
/>
<SwitchPreference
android:key="pref_key_review"
android:title="@string/pref_key_review"
android:summary="@string/pref_key_review_descr"
/>
<Preference
android:key="pref_key_review_time"
android:title="@string/pref_key_review_time"
android:summary="@string/pref_key_review_time_descr"
/>
<ListPreference
android:key="pref_key_read"
android:title="@string/pref_key_read"
android:summary="@string/pref_key_read_descr"
android:defaultValue="2"
android:entries="@array/pref_read_list_titles"
android:entryValues="@array/pref_read_list_values"
/>
</PreferenceCategory>
</PreferenceScreen>
我将不得不用安装的日历列表替换new CharSequence[]{"One", "Two", "Three"}
-这就是为什么必须从SettingsActivity类调用sf.addCustomList
的原因。
当我进入设置屏幕时,就会发生此错误(addCustomList()函数中setEntries()执行时的行号点):
FATAL EXCEPTION: main
Process: com.package1.novamowa, PID: 22093
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.package1.novamowa/com.silverdragon.kalafono.SettingsActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.preference.ListPreference.setEntries(java.lang.CharSequence[])' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3194)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3302)
at android.app.ActivityThread.-wrap12(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1891)
at android.os.Handler.dispatchMessage(Handler.java:108)
at android.os.Looper.loop(Looper.java:166)
at android.app.ActivityThread.main(ActivityThread.java:7425)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:245)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:921)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.preference.ListPreference.setEntries(java.lang.CharSequence[])' on a null object reference
at com.silverdragon.kalafono.SettingsActivity$SettingsFragment.addCustomList(SettingsActivity.java:47)
at com.silverdragon.kalafono.SettingsActivity.onCreate(SettingsActivity.java:35)
at android.app.Activity.performCreate(Activity.java:7383)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1218)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3147)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3302)
at android.app.ActivityThread.-wrap12(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1891)
at android.os.Handler.dispatchMessage(Handler.java:108)
at android.os.Looper.loop(Looper.java:166)
at android.app.ActivityThread.main(ActivityThread.java:7425)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:245)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:921)
我想知道-这个项目是从另一个项目复制而软件包名称已更改。它不应该影响findPreference()的执行,对吗? 请帮忙!
编辑:我已经解决了这个问题。
@SuppressLint("ValidFragment")
public static class SettingsFragment extends PreferenceFragmentCompat {
SettingsActivity invoker;
@SuppressLint("ValidFragment")
public SettingsFragment(SettingsActivity invoker) {
super();
this.invoker = invoker;
}
@Override
public void onCreatePreferences(Bundle savedInstanceState, String rootkey) {
setPreferencesFromResource(R.xml.pref_settings, rootkey);
CalendarList cl = invoker.getListOfCalendars();
String[] ids = cl.ids.toArray(new String[cl.ids.size()]);
String[] names = cl.names.toArray(new String[cl.names.size()]);
ListPreference customListPref = (ListPreference) findPreference("pref_key_calendar");
customListPref.setEntries(names);
customListPref.setEntryValues(ids);
}
}
使用invoker
作为参数将构造函数添加到SettingsFragments允许我回调getListOfCalendars()函数,并使用结果将其添加到层次结构中的相应ListPreference点。
我不知道为什么IDE强迫我添加此@SuppressLint(“ ValidFragment”)批注,但是程序可以正常工作,所以我不在乎:)。
如果有人认为我的解决方案不正确,我将很高兴听到您的建议。
干杯!