我的应用程序在方向改变时崩溃。发生这种情况时，我已经注意遵循默认建议，即每个 fragment 都有一个无参数构造函数，并且由于我已经在 MainActivity 中实现了 fragment ，因此它们被声明为静态。但我仍然面临同样的异常，就好像我没有这样做一样。
public class MainActivity extends FragmentActivity {
public static final String URL = "url";
public static final String ID = "id";
private SettingsPageAdapter pageAdapter;
private ViewPager pager;
private FrameLayout layoutTabBar;
public static class SettingsPageAdapter extends FragmentPagerAdapter {
private final List<Fragment> fragments;
public SettingsPageAdapter(FragmentManager fm) {
super(fm);
fragments = new ArrayList<Fragment>();
}
public void addWebViewItem(String url, String id) {
final Fragment settingsFragment = new SettingsWebView();
final Bundle bundle = new Bundle();
bundle.putString(URL, url);
bundle.putString(ID, id);
settingsFragment.setArguments(bundle);
this.fragments.add(settingsFragment);
}
public void addItem(Fragment f, String id) {
final Bundle bundle = new Bundle();
bundle.putString(ID, id);
f.setArguments(bundle);
this.fragments.add(f);
}
@Override
public Fragment getItem(int position) {
return this.fragments.get(position);
}
@Override
public int getCount() {
return this.fragments.size();
}
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction()
.add(R.id.bar, new BarFragment()).commit();
}
pageAdapter = new SettingsPageAdapter(getSupportFragmentManager());
pageAdapter.addWebViewItem("https://www.google.com", "WebView 1");
pageAdapter.addWebViewItem("https://m.bbc.co.uk", "WebView 2");
pageAdapter.addWebViewItem("http://thorbek.net", "WebView 3");
pageAdapter.addItem(new ContainerFragment(), "container");
pager = (ViewPager) findViewById(R.id.container);
pager.setOffscreenPageLimit(pageAdapter.getCount() - 1);
pager.setAdapter(pageAdapter);
pager.setOnPageChangeListener(new OnPageChangeListener() {
@Override
public void onPageSelected(int arg0) {
Log.d("PAGER", "onPageSelected");
}
@Override
public void onPageScrolled(int arg0, float arg1, int arg2) {
Log.d("PAGER", "onPageScrolled");
}
@Override
public void onPageScrollStateChanged(int arg0) {
Log.d("PAGER", "onPageScrollStateChanged");
final int currentItem = pager.getCurrentItem();
final BarFragment barFragment = (BarFragment) getSupportFragmentManager()
.findFragmentById(R.id.bar);
barFragment.setCurrentItem(currentItem);
}
});
layoutTabBar = (FrameLayout) findViewById(R.id.bar);
initAnimation();
}
private void initAnimation() {
...
}
public static class BarFragment extends Fragment {
private final List<Button> buttons = new ArrayList<Button>();
private int currentIndex = -1;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
final View rootView = inflater.inflate(R.layout.fragment_buttonbar,
container, false);
initButtons(rootView);
return rootView;
}
@SuppressWarnings("deprecation")
public void setCurrentItem(int index) {
if (currentIndex != index) {
resetButtons();
buttons.get(index).setBackgroundDrawable(
buttons.get(index).getContext().getResources()
.getDrawable(R.drawable.button_settings_pressed));
currentIndex = index;
}
}
@SuppressWarnings("deprecation")
private void initButtons(final View rootView) {
...
}
@SuppressWarnings("deprecation")
private void resetButtons() {
...
}
}
Java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.test/com.example.test.MainActivity}: android.support.v4.app.Fragment$InstantiationException: Unable to instantiate fragment com.example.test.MainActivity$BarFragment: make sure class name exists, is public, and has an empty constructor that is public
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2351)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2403)
at android.app.ActivityThread.access$700(ActivityThread.java:165)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1379)
at android.os.Handler.dispatchMessage(Handler.java:107)
at android.os.Looper.loop(Looper.java:194)
at android.app.ActivityThread.main(ActivityThread.java:5391)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:525)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
at dalvik.system.NativeStart.main(Native Method)
Caused by: android.support.v4.app.Fragment$InstantiationException: Unable to instantiate fragment com.example.test.MainActivity$BarFragment: make sure class name exists, is public, and has an empty constructor that is public
at android.support.v4.app.Fragment.instantiate(Fragment.java:435)
at android.support.v4.app.FragmentState.instantiate(Fragment.java:101)
at android.support.v4.app.FragmentManagerImpl.restoreAllState(FragmentManager.java:1823)
at android.support.v4.app.FragmentActivity.onCreate(FragmentActivity.java:264)
at com.example.test.MainActivity.onCreate(MainActivity.java:79)
at android.app.Activity.performCreate(Activity.java:5122)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1150)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2315)
Caused by: java.lang.IllegalAccessException: access to class not allowed
at java.lang.Class.newInstanceImpl(Native Method)
at java.lang.Class.newInstance(Class.java:1319)
at android.support.v4.app.Fragment.instantiate(Fragment.java:420)
MainActivity.java:79 位于 super.onCreate(savedInstanceState);
因此它会立即在 MainActivity 的 onCreate 中抛出。
最佳答案
异常情况非常明显。
make sure class name exists, is public, and has an empty constructor that is public
您的 BarFragment 类必须是公开的
public static class BarFragment extends Fragment
或者，您可以通过在创建 fragment 时执行以下操作来避免重新创建 fragment
fragment.setRetainInstance(true)
关于java - 方向改变时 fragment 崩溃，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/26867693/