android - PreferenceActivity 中的 ClassCastException

Question

我正在尝试从 Reto Meier 的 Android 2 应用程序开发一书中获取示例(第 202 页)。根据说明，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>

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);
  }

我不断收到 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

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>

我尝试使用整数数组，但没有用。我做错了什么？

Answer 1

我遇到了同样的问题——书中前面示例中的用户偏好数据在保存偏好数据时使用了不同的数据类型。

解决方案是在启动 AVD 时简单地选中“清除用户数据”复选框以摆脱旧的用户偏好设置。