PreferenceActivity中的ClassCastException

Question

PreferenceActivity中的ClassCastException

我试图从Reto Meier的Android 2应用程序开发书中找到一个例子来工作(第202页).根据我的说明,我创建了一个userpreferences.xml,如下所示:

<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android" >
  <CheckBoxPreference
    android:key="PREF_AUTO_UPDATE"
    android:title="Auto refresh"
    android:summary="Select to turn on automatic updating"
    android:defaultValue="true"  
   />
  <ListPreference
    android:key="PREF_UPDATE_FREQ"
    android:title="Refresh frequency"
    android:summary="Frequency at which to refresh earthquake list"
    android:entries="@array/update_freq_options"
    android:entryValues="@array/update_freq_values"
    android:dialogTitle="Refresh frequency"
    android:defaultValue="60"
  />
  <ListPreference
    android:key="PREF_MIN_MAG"
    android:title="Minimum magnitude"
    android:summary="Select the minimum magnitude earthquake to report"
    android:entries="@array/magnitude_options"
    android:entryValues="@array/magnitude"
    android:dialogTitle="Magnitude"
    android:defaultValue="3"
  />
</PreferenceScreen>

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我的Preferences类看起来像这样......

public class Preferences extends PreferenceActivity {
  SharedPreferences prefs;
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    addPreferencesFromResource(R.xml.userpreferences);
  }

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我一直得到一个ClassCastException:java.lang.ClassCastException:java.lang.Integer

12-16 09:28:14.349: ERROR/AndroidRuntime(287): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.dt.sample/com.dt.sample.Preferences}: java.lang.ClassCastException: java.lang.Integer
12-16 09:28:14.349: ERROR/AndroidRuntime(287):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
12-16 09:28:14.349: ERROR/AndroidRuntime(287):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
12-16 09:28:14.349: ERROR/AndroidRuntime(287):     at android.app.ActivityThread.access$2300(ActivityThread.java:125)
12-16 09:28:14.349: ERROR/AndroidRuntime(287):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
12-16 09:28:14.349: ERROR/AndroidRuntime(287):     at android.os.Handler.dispatchMessage(Handler.java:99)
12-16 09:28:14.349: ERROR/AndroidRuntime(287):     at android.os.Looper.loop(Looper.java:123)
12-16 09:28:14.349: ERROR/AndroidRuntime(287):     at android.app.ActivityThread.main(ActivityThread.java:4627)
12-16 09:28:14.349: ERROR/AndroidRuntime(287):     at java.lang.reflect.Method.invokeNative(Native Method)
12-16 09:28:14.349: ERROR/AndroidRuntime(287):     at java.lang.reflect.Method.invoke(Method.java:521)
12-16 09:28:14.349: ERROR/AndroidRuntime(287):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
12-16 09:28:14.349: ERROR/AndroidRuntime(287):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
12-16 09:28:14.349: ERROR/AndroidRuntime(287):     at dalvik.system.NativeStart.main(Native Method)
12-16 09:28:14.349: ERROR/AndroidRuntime(287): Caused by: java.lang.ClassCastException: java.lang.Integer
12-16 09:28:14.349: ERROR/AndroidRuntime(287):     at android.app.ContextImpl$SharedPreferencesImpl.getString(ContextImpl.java:2699)
12-16 09:28:14.349: ERROR/AndroidRuntime(287):     at android.preference.Preference.getPersistedString(Preference.java:1249)
12-16 09:28:14.349: ERROR/AndroidRuntime(287):     at android.preference.ListPreference.onSetInitialValue(ListPreference.java:232)
12-16 09:28:14.349: ERROR/AndroidRuntime(287):     at android.preference.Preference.dispatchSetInitialValue(Preference.java:1172)
12-16 09:28:14.349: ERROR/AndroidRuntime(287):     at android.preference.Preference.onAttachedToHierarchy(Preference.java:984)
12-16 09:28:14.349: ERROR/AndroidRuntime(287):     at android.preference.PreferenceGroup.addPreference(PreferenceGroup.java:156)
12-16 09:28:14.349: ERROR/AndroidRuntime(287):     at android.preference.PreferenceGroup.addItemFromInflater(PreferenceGroup.java:97)
12-16 09:28:14.349: ERROR/AndroidRuntime(287):     at android.preference.PreferenceGroup.addItemFromInflater(PreferenceGroup.java:38)
12-16 09:28:14.349: ERROR/AndroidRuntime(287):     at android.preference.GenericInflater.rInflate(GenericInflater.java:488)
12-16 09:28:14.349: ERROR/AndroidRuntime(287):     at android.preference.GenericInflater.inflate(GenericInflater.java:326)
12-16 09:28:14.349: ERROR/AndroidRuntime(287):     at android.preference.GenericInflater.inflate(GenericInflater.java:263)
12-16 09:28:14.349: ERROR/AndroidRuntime(287):     at android.preference.PreferenceManager.inflateFromResource(PreferenceManager.java:251)
12-16 09:28:14.349: ERROR/AndroidRuntime(287):     at android.preference.PreferenceActivity.addPreferencesFromResource(PreferenceActivity.java:262)
12-16 09:28:14.349: ERROR/AndroidRuntime(287):     at com.dt.sample.Preferences.onCreate(Preferences.java:24)
12-16 09:28:14.349: ERROR/AndroidRuntime(287):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
12-16 09:28:14.349: ERROR/AndroidRuntime(287):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
12-16 09:28:14.349: ERROR/AndroidRuntime(287):     ... 11 more

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arrays.xml看起来像这样......

<resources>
  <string-array name="update_freq_options">
    <item>Every Minute</item>
    <item>5 minutes</item>
    <item>10 minutes</item>
    <item>15 minutes</item>
    <item>Every Hour</item>
  </string-array>
  <array name="magnitude">
    <item>3</item>
    <item>5</item>
    <item>6</item>
    <item>7</item>
    <item>8</item>
  </array>
  <string-array name="magnitude_options">
    <item>3</item>
    <item>5</item>
    <item>6</item>
    <item>7</item>
    <item>8</item>
  </string-array>
  <array name="update_freq_values">
    <item>1</item>
    <item>5</item>
    <item>10</item>
    <item>15</item>
    <item>60</item>
  </array>
</resources>

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我尝试使用整数数组,但没有帮助.我究竟做错了什么？请帮忙.谢谢.