android - PreferenceActivity 在方向更改时崩溃

Question

我正在编写一个带有 PreferenceFragment 的 PreferenceActivity，当设备的方向发生变化时(即从横向到纵向)，将抛出一个 InstantiationException反之亦然)。此外，如果我在弹出的对话框中点击“确定”(“不幸的是，你的应用程序已停止。”)，主要 Activity 将重新启动，并且 PreferenceActivity 在新方向上完美运行，直到它被更改再次。我似乎无法在网上找到任何关于此的信息。堆栈跟踪:

05-26 09:28:10.860: E/AndroidRuntime(3439): FATAL EXCEPTION: main
05-26 09:28:10.860: E/AndroidRuntime(3439): Process: com.example.myapp, PID: 3439
05-26 09:28:10.860: E/AndroidRuntime(3439): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.myapp/com.example.myapp.SettingsActivity}: android.app.Fragment$InstantiationException: Unable to instantiate fragment com.devgregw.strikedistance_androidphoneandtablet.SettingsActivity$2: make sure class name exists, is public, and has an empty constructor that is public
05-26 09:28:10.860: E/AndroidRuntime(3439):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
05-26 09:28:10.860: E/AndroidRuntime(3439):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
05-26 09:28:10.860: E/AndroidRuntime(3439):     at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:3738)
05-26 09:28:10.860: E/AndroidRuntime(3439):     at android.app.ActivityThread.access$900(ActivityThread.java:135)
05-26 09:28:10.860: E/AndroidRuntime(3439):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1202)
05-26 09:28:10.860: E/AndroidRuntime(3439):     at android.os.Handler.dispatchMessage(Handler.java:102)
05-26 09:28:10.860: E/AndroidRuntime(3439):     at android.os.Looper.loop(Looper.java:136)
05-26 09:28:10.860: E/AndroidRuntime(3439):     at android.app.ActivityThread.main(ActivityThread.java:5027)
05-26 09:28:10.860: E/AndroidRuntime(3439):     at java.lang.reflect.Method.invokeNative(Native Method)
05-26 09:28:10.860: E/AndroidRuntime(3439):     at java.lang.reflect.Method.invoke(Method.java:515)
05-26 09:28:10.860: E/AndroidRuntime(3439):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
05-26 09:28:10.860: E/AndroidRuntime(3439):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
05-26 09:28:10.860: E/AndroidRuntime(3439):     at de.robv.android.xposed.XposedBridge.main(XposedBridge.java:132)
05-26 09:28:10.860: E/AndroidRuntime(3439):     at dalvik.system.NativeStart.main(Native Method)
05-26 09:28:10.860: E/AndroidRuntime(3439): Caused by: android.app.Fragment$InstantiationException: Unable to instantiate fragment com.example.myapp.SettingsActivity$2: make sure class name exists, is public, and has an empty constructor that is public
05-26 09:28:10.860: E/AndroidRuntime(3439):     at android.app.Fragment.instantiate(Fragment.java:601)
05-26 09:28:10.860: E/AndroidRuntime(3439):     at android.app.FragmentState.instantiate(Fragment.java:98)
05-26 09:28:10.860: E/AndroidRuntime(3439):     at android.app.FragmentManagerImpl.restoreAllState(FragmentManager.java:1759)
05-26 09:28:10.860: E/AndroidRuntime(3439):     at android.app.Activity.onCreate(Activity.java:899)
05-26 09:28:10.860: E/AndroidRuntime(3439):     at android.preference.PreferenceActivity.onCreate(PreferenceActivity.java:514)
05-26 09:28:10.860: E/AndroidRuntime(3439):     at com.example.myapp.SettingsActivity.onCreate(SettingsActivity.java:23)
05-26 09:28:10.860: E/AndroidRuntime(3439):     at android.app.Activity.performCreate(Activity.java:5231)
05-26 09:28:10.860: E/AndroidRuntime(3439):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
05-26 09:28:10.860: E/AndroidRuntime(3439):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
05-26 09:28:10.860: E/AndroidRuntime(3439):     ... 13 more
05-26 09:28:10.860: E/AndroidRuntime(3439): Caused by: java.lang.InstantiationException: can't instantiate class com.example.myapp.SettingsActivity$2; no empty constructor
05-26 09:28:10.860: E/AndroidRuntime(3439):     at java.lang.Class.newInstanceImpl(Native Method)
05-26 09:28:10.860: E/AndroidRuntime(3439):     at java.lang.Class.newInstance(Class.java:1208)
05-26 09:28:10.860: E/AndroidRuntime(3439):     at android.app.Fragment.instantiate(Fragment.java:590)
05-26 09:28:10.860: E/AndroidRuntime(3439):     ... 21 more

SettingsActivity.java:

package com.example.myapp;

import android.content.SharedPreferences;
import android.content.SharedPreferences.OnSharedPreferenceChangeListener;
import android.os.Bundle;
import android.preference.ListPreference;
import android.preference.Preference;
import android.preference.PreferenceActivity;
import android.preference.PreferenceFragment;
import android.preference.PreferenceGroup;

public class SettingsActivity extends PreferenceActivity {

    public OnSharedPreferenceChangeListener changeListener;
    public SharedPreferences preferences;
    public PreferenceFragment fragment;

    public SettingsActivity() {
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        changeListener = new OnSharedPreferenceChangeListener() {

            @Override
            public void onSharedPreferenceChanged(
                    SharedPreferences sharedPreferences, String key) {
                Preference preference = fragment.findPreference(key);
                if (preference instanceof ListPreference) {
                    ListPreference listPreference = (ListPreference) preference;
                    listPreference.setSummary(listPreference.getEntry());
                }
            }

        };
        fragment = new PreferenceFragment() {

            @Override
            public void onCreate(Bundle savedInstanceState) {
                super.onCreate(savedInstanceState);
                addPreferencesFromResource(R.xml.preferences);
                preferences = getPreferenceScreen().getSharedPreferences();
            }

            @Override
            public void onResume() {
                super.onResume();
                for (int i = 0; i < getPreferenceScreen().getPreferenceCount(); ++i) {
                    Preference preference = getPreferenceScreen()
                            .getPreference(i);
                    if (preference instanceof PreferenceGroup) {
                        PreferenceGroup preferenceGroup = (PreferenceGroup) preference;
                        for (int j = 0; j < preferenceGroup
                                .getPreferenceCount(); ++j) {
                            updatePreference(preferenceGroup.getPreference(j));
                        }
                    } else {
                        updatePreference(preference);
                    }
                }
            }

            public void updatePreference(Preference preference) {
                if (preference instanceof ListPreference) {
                    ListPreference listPreference = (ListPreference) preference;
                    listPreference.setSummary(listPreference.getEntry());
                }
            }
        };
        getFragmentManager().beginTransaction()
                .replace(android.R.id.content, fragment).commit();
    }

    @Override
    protected void onResume() {
        super.onResume();
        preferences.registerOnSharedPreferenceChangeListener(changeListener);
    }

    @Override
    protected void onPause() {
        super.onPause();
        preferences.unregisterOnSharedPreferenceChangeListener(changeListener);
    }
}

Answer 1

你的 fragment 应该有一个构造函数

Caused by: android.app.Fragment$InstantiationException: Unable to instantiate fragment com.example.myapp.SettingsActivity$2: make sure class name exists, is public, and has an empty constructor that is public

同时将 Fragment 声明作为 static 内部类或另一个 .java 文件从该函数中取出。

有关更多信息，您可以阅读文档 here .或者您可以查看有关 Fragments 的 Android 培训指南 here .