java - 由 : java. lang.ClassCastException : com. example.mayank.sunshine.SettingsActivity 引起，无法转换为 android.app.Activity

Question

package com.example.mayank.sunshine;

import android.os.Bundle;
import android.preference.ListPreference;
import android.preference.Preference;
import android.preference.PreferenceActivity;
import android.preference.PreferenceFragment;
import android.preference.PreferenceManager;

/**
 * A {@link PreferenceActivity} that presents a set of application settings.
 * <p>
 * See <a href="http://developer.android.com/design/patterns/settings.html">
 * Android Design: Settings</a> for design guidelines and the <a
 * href="http://developer.android.com/guide/topics/ui/settings.html">Settings
 * API Guide</a> for more information on developing a Settings UI.
 */
public class SettingsActivity extends PreferenceFragment
        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)));
    }

    /**
     * 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;
    }

}

上面的代码显示以下错误: 引起原因:java.lang.ClassCastException:com.example.mayank.sunshine.SettingsActivity无法转换为android.app.Activity

之前的代码有“SettingsActivity extends PreferenceActivity”，但某些功能显示为已弃用，并且我被引导使用 PreferenceFragment 类，因此在更改父类时，开始弹出错误。此外， list 文件的以下部分在 android:name=".SettingsActivity"

中显示错误

<activity
    android:name=".SettingsActivity"
    android:label="@string/title_activity_settings"
    android:parentActivityName=".MainActivity"
    android:theme="@style/AppTheme.NoActionBar" >
    <meta-data
        android:name="android.support.PARENT_ACTIVITY"
        android:value="com.example.mayank.sunshine.MainActivity" />
</activity>

Answer 1

The above code shows the following error: Caused by: java.lang.ClassCastException: com.example.mayank.sunshine.SettingsActivity cannot be cast to android.app.Activity

那是因为您的SettingsActivity在其继承链中没有Activity。 SettingsActivity 继承自 Fragment，而 Fragment 又继承于 Object。

The code previously had "SettingsActivity extends PreferenceActivity", but this class is deprecated in newer APIs

PreferenceActivity 在任何版本的 Android 中都不会被弃用，直到 API 级别 23。