我是使用 PreferenceActivity 的新手。
任务:允许用户从首选项中选择程序布局
问题:在 PreferenceList 中选择一个选项会导致 NullPointerException
出现异常:在 android.preference.ListPreference.onDialogClosed()
(缩短)代码:
private static final String PREF_LAYOUT_KEY = "PrefLayout";
private static final int DEFAULT_LAYOUT = LayoutHelper.LAYOUT_DOUBLE ;
private static int mListLayout = DEFAULT_LAYOUT ;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
SharedPreferences pref = PreferenceManager.getDefaultSharedPreferences(this);
pref.registerOnSharedPreferenceChangeListener(this);
mListLayout = pref.getInt(PREF_LAYOUT_KEY, DEFAULT_LAYOUT);
}
@Override
public void onSharedPreferenceChanged(SharedPreferences pref,
String key) {
Log.v(TAG, "OnSharedPreferencesChanged run" ); // TODO Testing Purposes
if( key.equals( PREF_LAYOUT_KEY ) ){
mListLayout = pref.getInt(key, DEFAULT_LAYOUT);
}
}
[偏好活动]
public class Preferences extends PreferenceActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
addPreferencesFromResource(R.xml.pref);
}
}
[res/xml/pref.xml]
<PreferenceCategory
android:title="@string/pref_cat1_title">
<ListPreference
android:title="@string/pref_layout_name"
android:summary="@+id/pref_chosen_layout"
android:key="PrefLayout"
android:entries="@array/prefLayoutOptions"
android:entryValues="@array/prefLayoutOptionsValues"
/>
</PreferenceCategory>
[字符串.xml]
<string name="pref_cat1_title">Layout</string>
<string name="pref_layout_name">"Layout of list"</string>
<array name="prefLayoutOptions">
<item>Layout 1 (single)</item>
<item>Layout 2 (double)</item>
<item>Layout 3 (triple)</item>
<item>Layout 4 (quad)</item>
</array>
<array name="prefLayoutOptionsValues">
<item>50</item>
<item>51</item>
<item>52</item>
<item>53</item>
</array>
记录 OnSharedPreferencesChanged 正在运行的那段代码永远不会到达那里。
谁能看到我哪里出错了?
编辑。这是堆栈跟踪的顶部:
E/AndroidRuntime( 2707): java.lang.NullPointerException
E/AndroidRuntime( 2707): at android.preference.ListPreference.onDialogClosed(ListPreference.java:218)
E/AndroidRuntime( 2707): at android.preference.DialogPreference.onDismiss(DialogPreference.java:384)
E/AndroidRuntime( 2707): at android.app.Dialog$ListenersHandler.handleMessage(Dialog.java:1047)
E/AndroidRuntime( 2707): at android.os.Handler.dispatchMessage(Handler.java:99)