以下是pref_xml.xml文件中Preferences的代码 此文件定义天气应用程序的设置首选项，该应用程序将该位置作为编辑文本首选项和单位作为列表首选项
<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">
<EditTextPreference
android:title="@string/pref_location_label"
android:key="@string/pref_location_key"
android:defaultValue="@string/pref_location_default"
android:inputType="text"
android:singleLine="true" />
<ListPreference
android:title="@string/pref_units_label"
android:key="@string/pref_units_key"
android:defaultValue="@string/pref_units_metric"
android:entryValues="@array/pref_units_values"
android:entries="@array/pref_units_options"
/>
</PreferenceScreen>
以下是arrays.xml文件的代码，该文件为用户的单位选项定义了pref_units_values和pref_units_options
<resources>
<string-array name="pref_units_options">
<item>@string/pref_units_label_metric</item>
<item>@string/pref_units_label_imperial</item>
</string-array>
<string-array name="pref_units_values">
<item>@string/pref_units_metric</item>
<item>@string/pref_units_imperial</item>
</string-array>
</resources>
以下是定义文件中所有字符串的代码
<resources>
<!-- Label for the location preference [CHAR LIMIT=30] -->
<string name="pref_location_label">Location</string>
<!-- Key name for storing location in SharedPreferences [CHAR LIMIT=NONE] -->
<string name="pref_location_key" translatable="false">location</string>
<!-- Default postal code for location preference [CHAR LIMIT=NONE] -->
<string name="pref_location_default" translatable="false">94043</string>
<!-- Label for the temperature units preference [CHAR LIMIT=30] -->
<string name="pref_units_label">Temperature Units</string>
<!-- Label for metric option in temperature unit preference [CHAR LIMIT=25] -->
<string name="pref_units_label_metric">Metric</string>
<!-- Label for imperial option in temperature unit preference [CHAR LIMIT=25] -->
<string name="pref_units_label_imperial">Imperial</string>
<!-- Key name for temperature unit preference in SharedPreferences [CHAR LIMIT=NONE] -->
<string name="pref_units_key" translatable="false">units</string>
<!-- Value in SharedPreferences for metric temperature unit option [CHAR LIMIT=NONE] -->
<string name="pref_units_metric" translatable="false">metric</string>
<!-- Value in SharedPreferences for imperial temperature unit option [CHAR LIMIT=NONE] -->
<string name="pref_units_imperial" translatable="false">imperial</string>
</resources>
接下来是SettingsActivity.java文件的代码，该文件链接pref_general.xml文件中的首选项。
public class SettingsActivity extends PreferenceActivity
implements Preference.OnPreferenceChangeListener {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Add 'general' preferences, defined in the XML file
addPreferencesFromResource(R.xml.pref_general);
// For all preferences, attach an OnPreferenceChangeListener so the UI summary can be
// updated when the preference changes.
bindPreferenceSummaryToValue(findPreference(getString(R.string.pref_location_key)));
//bindPreferenceSummaryToValue(findPreference(getString(R.string.pref_units_key)));
}
/**
* Attaches a listener so the summary is always updated with the preference value.
* Also fires the listener once, to initialize the summary (so it shows up before the value
* is changed.)
*/
private void bindPreferenceSummaryToValue(Preference preference) {
// Set the listener to watch for value changes.
preference.setOnPreferenceChangeListener(this);
// Trigger the listener immediately with the preference's
// current value.
onPreferenceChange(preference,
PreferenceManager
.getDefaultSharedPreferences(preference.getContext())
.getString(preference.getKey(), ""));
}
@Override
public boolean onPreferenceChange(Preference preference, Object value) {
String stringValue = value.toString();
if (preference instanceof ListPreference) {
// For list preferences, look up the correct display value in
// the preference's 'entries' list (since they have separate labels/values).
ListPreference listPreference = (ListPreference) preference;
int prefIndex = listPreference.findIndexOfValue(stringValue);
if (prefIndex >= 0) {
preference.setSummary(listPreference.getEntries()[prefIndex]);
}
} else {
// For other preferences, set the summary to the value's simple string representation.
preference.setSummary(stringValue);
}
return true;
}
}
假设所有类和包都已导入。当运行上述文件集合以及执行使用首选项值来生成对天气数据库api的http请求的任务的其他活动时，应用程序会在单击菜单中的设置按钮时崩溃。 Logcat条目显示ClassCastException，具有以下详细信息。
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.meet.mysunshine/com.meet.mysunshine.SettingsActivity}: java.lang.ClassCastException: java.lang.Boolean cannot be cast to java.lang.String
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2426)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2490)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1354)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5443)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:728)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
Caused by: java.lang.ClassCastException: java.lang.Boolean cannot be cast to java.lang.String
at android.app.SharedPreferencesImpl.getString(SharedPreferencesImpl.java:225)
at android.preference.Preference.getPersistedString(Preference.java:1472)
at android.preference.ListPreference.onSetInitialValue(ListPreference.java:295)
at android.preference.Preference.dispatchSetInitialValue(Preference.java:1388)
at android.preference.Preference.onAttachedToHierarchy(Preference.java:1182)
at android.preference.PreferenceGroup.addPreference(PreferenceGroup.java:164)
at android.preference.PreferenceGroup.addItemFromInflater(PreferenceGroup.java:105)
at android.preference.PreferenceGroup.addItemFromInflater(PreferenceGroup.java:104)
at android.preference.GenericInflater.rInflate(GenericInflater.java:490)
at android.preference.GenericInflater.inflate(GenericInflater.java:327)
at android.preference.GenericInflater.inflate(GenericInflater.java:264)
at android.preference.PreferenceManager.inflateFromResource(PreferenceManager.java:273)
at android.preference.PreferenceActivity.addPreferencesFromResource(PreferenceActivity.java:1521)
at com.meet.mysunshine.SettingsActivity.onCreate(SettingsActivity.java:38)
at android.app.Activity.performCreate(Activity.java:6245)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1130)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2379)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2490)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1354)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5443)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:728)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
PLS。提供帮助查找点生成异常。提前致谢。 并随意询问有关代码的任何其他详细信息。 谢谢！