方向更改时程序崩溃

Question

这是进步对话片段的示例程序。通常它工作正常，但方向改变了它崩溃..

出现此错误

java.lang.IllegalSt    ateException: Can not perform this action after onSaveInstanceSt    ate
at android.support.v4.app.FragmentManagerImpl.checkSt    ateLoss(FragmentManager.java:1375)
at android.support.v4.app.FragmentManagerImpl.enqueueAction(FragmentManager.java:1393)
at android.support.v4.app.BackStackRecord.commitInternal(BackStackRecord.java:636)
at android.support.v4.app.BackStackRecord.commit(BackStackRecord.java:615)
at android.support.v4.app.DialogFragment.show(DialogFragment.java:138)
at com.inntot.langtest.MainActivity$LongOper    ation.onPostExecute(MainActivity.java:75)
at com.inntot.langtest.MainActivity$LongOper    ation.onPostExecute(MainActivity.java:57)
at android.os.AsyncTask.finish(AsyncTask.java:632)
at android.os.AsyncTask.access$600(AsyncTask.java:177)
at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:645)
at android.os.Handler.disp    atchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5253)
at java.lang.reflect.Method.invoke(N    ative Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
at de.robv.android.xposed.XposedBridge.main(XposedBridge.java:117)

主要活动

public class MainActivity extends ActionBarActivity 
{
Button change;
ProgressDialogFragment p;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    change = (Button)findViewById(R.id.buttonchange);
    change.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {

            p = ProgressDialogFragment.newInstance("Hai","Hello");
            p.show(getSupportFragmentManager(),"update");
            new LongOperation().execute("");

        }
    });

}

private class LongOperation extends AsyncTask<String, Void, String> {
    @Override
    protected String doInBackground(String... params) {
        for (int i = 0; i < 5; i++) {
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                Thread.interrupted();
            }
        }
        return "Executed";
    }

    @Override
    protected void onPostExecute(String result) {
      p.dismissDialog();
        p = ProgressDialogFragment.newInstance("Hai","Home");
        p.show(getSupportFragmentManager(),"update");

    }

    @Override
    protected void onPreExecute() {}

    @Override
    protected void onProgressUpdate(Void... values) {}
}
}

进度对话片段

 public class ProgressDialogFragment extends DialogFragment
{
String Title,Message;
static ProgressDialogFragment newInstance(String Title,String Message){
    ProgressDialogFragment PDF= new ProgressDialogFragment();
    Bundle bundle = new Bundle();
    bundle.putString("Title",Title);
    bundle.putString("Message",Message);
    PDF.setArguments(bundle);
    return  PDF;
}
@Override
public void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    setCancelable(false);
    setRetainInstance(true);
}

@Override
public Dialog onCreateDialog(Bundle savedInstanceState)
{
    ProgressDialog dialog = new ProgressDialog(getActivity(), getTheme());
    dialog.setTitle(getArguments().getString("Title"));
    dialog.setMessage(getArguments().getString("Message"));
    dialog.setIndeterminate(true);
    dialog.setProgressStyle(ProgressDialog.STYLE_SPINNER);
    return dialog;
}
public void dismissDialog()
{
    dismiss();
}
@Override
public void onDestroyView() {
    if (getDialog() != null && getRetainInstance())
        getDialog().setOnDismissListener(null);
    super.onDestroyView();
}
}

任何人都可以帮我解决问题......