我对fragments比较陌生，我有一个活动，其中包含一些使用fragments和viewpager的选项卡。
我的问题是，每当我改变方向或进入主屏幕时，我的应用程序就会崩溃。
以下是我的活动：
public class MainActivity extends SherlockFragmentActivity {
ActionBar actionBar;
ViewPager mPager;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
actionBar = getSupportActionBar();
actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
mPager = (ViewPager) findViewById(R.id.pager);
FragmentManager fm = getSupportFragmentManager();
ViewPager.SimpleOnPageChangeListener pageChangeListener = new ViewPager.SimpleOnPageChangeListener(){
@Override
public void onPageSelected(int position) {
super.onPageSelected(position);
actionBar.setSelectedNavigationItem(position);
}
};
mPager.setOnPageChangeListener(pageChangeListener);
MyFragmentPagerAdapter fragmentPagerAdapter = new MyFragmentPagerAdapter(fm);
mPager.setAdapter(fragmentPagerAdapter);
actionBar.setDisplayShowTitleEnabled(true);
ActionBar.TabListener tabListener = new ActionBar.TabListener() {
@Override
public void onTabUnselected(Tab tab, FragmentTransaction ft) {
}
@Override
public void onTabSelected(Tab tab, FragmentTransaction ft) {
mPager.setCurrentItem(tab.getPosition());
}
@Override
public void onTabReselected(Tab tab, FragmentTransaction ft) {
}
};
Tab firstTab = mActionBar.newTab().setText("First Tab").setTabListener(tabListener);
actionBar.addTab(firstTab);
Tab secondTab = mActionBar.newTab()
.setText("Second Tab")
.setTabListener(tabListener);
actionBar.addTab(secondTab);
}
}
…下面是我的一个片段：
public class FirstFragment extends SherlockFragment implements ActionBar.TabListener{
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragmentone, container, false);
// Stuff...
return view;
}
@Override
public void onStart() {
super.onStart();
}
}
…我的片段适配器：
public class MyFragmentPagerAdapter extends FragmentPagerAdapter{
final int PAGE_COUNT = 2;
public MyFragmentPagerAdapter(FragmentManager fm) {
super(fm);
}
@Override
public Fragment getItem(int arg0) {
Bundle data = new Bundle();
switch(arg0){
case 0:
FirstFragment firstFragment = new FirstFragment();
data.putInt("current_page", arg0+1);
firstFragment.setArguments(data);
return firstFragment;
case 1:
SecondFragment secondFragment = new SecondFragment();
data.putInt("current_page", arg0+1);
secondFragment.setArguments(data);
return secondFragment;
}
return null;
}
@Override
public int getCount() {
return PAGE_COUNT;
}
}
…这是我所有的活动xml文件：
<android.support.v4.view.ViewPager
android:id="@+id/pager"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
/>
</RelativeLayout>
请帮忙，这让我头疼。
如果有帮助的话，我正在使用ActionBarSherlock库。
编辑：这是我的日志当它崩溃的时候
11-27 22:44:14.590: D/dalvikvm(803): newInstance failed: no <init>()
11-27 22:44:14.599: D/AndroidRuntime(803): Shutting down VM
11-27 22:44:14.599: W/dalvikvm(803): threadid=1: thread exiting with uncaught exception (group=0x40a70930)
11-27 22:44:14.669: W/Trace(700): Unexpected value from nativeGetEnabledTags: 0
11-27 22:44:14.760: E/AndroidRuntime(803): FATAL EXCEPTION: main
11-27 22:44:14.760: E/AndroidRuntime(803): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.pk.chemhelp/com.pk.chemhelp.Debug}: android.support.v4.app.Fragment$InstantiationException: Unable to instantiate fragment com.pk.chemhelp.Debug$FirstFragment: make sure class name exists, is public, and has an empty constructor that is public
11-27 22:44:14.760: E/AndroidRuntime(803): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
11-27 22:44:14.760: E/AndroidRuntime(803): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
11-27 22:44:14.760: E/AndroidRuntime(803): at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:3692)
11-27 22:44:14.760: E/AndroidRuntime(803): at android.app.ActivityThread.access$700(ActivityThread.java:141)
11-27 22:44:14.760: E/AndroidRuntime(803): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1240)
11-27 22:44:14.760: E/AndroidRuntime(803): at android.os.Handler.dispatchMessage(Handler.java:99)
11-27 22:44:14.760: E/AndroidRuntime(803): at android.os.Looper.loop(Looper.java:137)
11-27 22:44:14.760: E/AndroidRuntime(803): at android.app.ActivityThread.main(ActivityThread.java:5039)
11-27 22:44:14.760: E/AndroidRuntime(803): at java.lang.reflect.Method.invokeNative(Native Method)
11-27 22:44:14.760: E/AndroidRuntime(803): at java.lang.reflect.Method.invoke(Method.java:511)
11-27 22:44:14.760: E/AndroidRuntime(803): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
11-27 22:44:14.760: E/AndroidRuntime(803): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
11-27 22:44:14.760: E/AndroidRuntime(803): at dalvik.system.NativeStart.main(Native Method)
11-27 22:44:14.760: E/AndroidRuntime(803): Caused by: android.support.v4.app.Fragment$InstantiationException: Unable to instantiate fragment com.pk.chemhelp.Debug$FirstFragment: make sure class name exists, is public, and has an empty constructor that is public
11-27 22:44:14.760: E/AndroidRuntime(803): at android.support.v4.app.Fragment.instantiate(Fragment.java:395)
11-27 22:44:14.760: E/AndroidRuntime(803): at android.support.v4.app.FragmentState.instantiate(Fragment.java:96)
11-27 22:44:14.760: E/AndroidRuntime(803): at android.support.v4.app.FragmentManagerImpl.restoreAllState(FragmentManager.java:1726)
11-27 22:44:14.760: E/AndroidRuntime(803): at android.support.v4.app.FragmentActivity.onCreate(FragmentActivity.java:198)
11-27 22:44:14.760: E/AndroidRuntime(803): at com.pk.chemhelp.Debug.onCreate(Debug.java:63)
11-27 22:44:14.760: E/AndroidRuntime(803): at android.app.Activity.performCreate(Activity.java:5104)
11-27 22:44:14.760: E/AndroidRuntime(803): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
11-27 22:44:14.760: E/AndroidRuntime(803): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
11-27 22:44:14.760: E/AndroidRuntime(803): ... 12 more
11-27 22:44:14.760: E/AndroidRuntime(803): Caused by: java.lang.InstantiationException: can't instantiate class com.pk.chemhelp.Debug$FirstFragment; no empty constructor
11-27 22:44:14.760: E/AndroidRuntime(803): at java.lang.Class.newInstanceImpl(Native Method)
11-27 22:44:14.760: E/AndroidRuntime(803): at java.lang.Class.newInstance(Class.java:1319)
11-27 22:44:14.760: E/AndroidRuntime(803): at android.support.v4.app.Fragment.instantiate(Fragment.java:384)
11-27 22:44:14.760: E/AndroidRuntime(803): ... 19 more
11-27 22:44:14.880: W/ActivityManager(290): Force finishing activity com.pk.chemhelp/.Debug
11-27 22:44:14.950: W/Trace(519): Unexpected value from nativeGetEnabledTags: 0
最佳答案
异常很明显，android需要完全访问您的类，以便在需要时（比如在配置更改时）实例化它。问题是，您将Fragment声明为FirstFragment类中的内部类，android系统无法实例化Debug，因为内部类总是绑定到封闭类的实例（在您的示例中为FirstFragment），因此Debug不能只是简单地实例化。
解决方案是将FirstFragment类与FirstFragment类分开，或者将Debug放在自己的Java文件中，或者将其保存在FirstFragment类中并使其成为cc>（因此它不再绑定到Debug类的实例）：
public static class FirstFragment extends SherlockFragment implements ActionBar.TabListener{