从 ListPreference 中选择选项时,PreferenceActivity 给出 NullPointerException
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. choice.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]
<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>
记录正在运行的 OnSharedPreferencesChanged 的代码永远不会到达那里。
有人能看出我哪里出了问题吗?
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)
I'm new to using the PreferenceActivity.
Task: Allow user to choose the program layout from the Preferences
Problem: Selecting an option in the PreferenceList causes a NullPointerException
Exception arises: At android.preference.ListPreference.onDialogClosed()
(Shortened) Code:
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]
<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>
The bit of code that logs OnSharedPreferencesChanged being run never gets there.
Can anybody see where I've gone wrong?
EDIT. Here's the top of the stack trace:
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)
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评论(3)
这会失败,因为首选项是字符串,而不是整数。
将它们更改为
。这是示例项目,演示了列表首选项
。That will fail, because the preference is a string, not an int.
Change these to
<string-array>
. Here is a sample project demonstrating the use of aListPreference
.我遇到了同样的问题。看来你只能使用字符串值:
http://code.google.com/p/android/issues/detail ?id=2096
/Håkan
I encountered the same problem. It seems you can only use string values:
http://code.google.com/p/android/issues/detail?id=2096
/Håkan
我认为您需要在活动中为您的首选项设置首选项更改侦听器,尝试将其放入活动的 onCreate 中:
I think you need to set preference change listener for your preferences right at the activity, try putting that to the activity's onCreate: