当从ListPreference中选择选项时,PreferenceActivity会给出NullPointerException

Question

我是新手使用PreferenceActivity.

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);
    }
}

[PreferenceActivity]

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>

[strings.xml中]

<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>

记录运行OnSharedPreferencesChanged的代码位从未到达.

谁能看到我出错的地方？

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)

Answer 1

mListLayout = pref.getInt(PREF_LAYOUT_KEY, DEFAULT_LAYOUT);

这将失败,因为首选项是字符串,而不是int.

<array name="prefLayoutOptions">
<array name="prefLayoutOptionsValues">

将这些更改为<string-array>.这是一个展示a的使用的示例项目ListPreference.

Answer 2

我遇到了同样的问题.您似乎只能使用字符串值:http: //code.google.com/p/android/issues/detail？id = 2096

/哈坎