viewpager显示第二个fragment的时候menu总会不显示

Question

package com.testing.simplesp.widget;

import android.content.Context;
import android.support.v4.view.ViewPager;
import android.util.AttributeSet;
import android.view.View;
import android.webkit.WebView;
import android.widget.ScrollView;

import com.testing.simplesp.R;

public class MyViewPager extends ViewPager {

public MyViewPager(Context context) {
    super(context);
}

public MyViewPager(Context context, AttributeSet attrs) {
    super(context, attrs);
}

@Override
protected boolean canScroll(View v, boolean checkV, int dx, int x, int y) {
    ScrollView sv = (ScrollView) v.findViewById(R.id.sv); //res ID
    WebView wv_doc = (WebView) v.findViewById(R.id.wv_doc); //res ID
    System.out.println(sv.getVisibility() + ":" + wv_doc.getVisibility());
    System.out.println(v.getTag());
    if (sv != null && sv.getVisibility() == View.VISIBLE) {
        return sv.canScrollHorizontally(-dx);
    }
    if (wv_doc != null && wv_doc.getVisibility() == View.VISIBLE) {
        return super.canScroll(v, checkV, dx, x, y);
    }
    return super.canScroll(v, checkV, dx, x, y);
}

}

package com.testing.simplesp.fragment;

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.webkit.WebChromeClient;
import android.webkit.WebSettings;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.RelativeLayout;
import android.widget.ScrollView;
import android.widget.TextView;

import com.testing.simplesp.R;
import com.testing.simplesp.adapter.Document.DocumentAdapter;
import com.testing.simplesp.domain.DocumentItem;

/**

• A simple {@link Fragment} subclass.
  */
  public class DocumentDetailFragment extends Fragment {

  private WebView wv_doc;
  private TextView tv_title;
  private TextView tv_unit;
  private TextView tv_content;
  private Toolbar mToolbar;
  private ScrollView sv;
  private DocumentItem.Data mData;
  private boolean isWebView = false;
  private boolean hasLoad = false;
  private View mView;
  private RelativeLayout mRl;

  public DocumentDetailFragment() {
  }

  public static DocumentDetailFragment newInstance(int position) {
  DocumentDetailFragment fragment = new DocumentDetailFragment();
  Bundle bundle = new Bundle();
  bundle.putInt("position", position);
  fragment.setArguments(bundle);
  return fragment;
  }

  @Override
  public View onCreateView(LayoutInflater inflater, ViewGroup container,
  Bundle savedInstanceState) {
  mView = inflater.inflate(R.layout.fragment_document_detail, container, false);
  initView();
  initData();
  return mView;

  }

  private void initView() {
  setHasOptionsMenu(true);
  mRl = (RelativeLayout) mView.findViewById(R.id.rl);
  wv_doc = (WebView) mView.findViewById(R.id.wv_doc);
  sv = (ScrollView) mView.findViewById(R.id.sv);
  tv_title = (TextView) mView.findViewById(R.id.tv_title);
  tv_unit = (TextView) mView.findViewById(R.id.tv_unit);
  tv_content = (TextView) mView.findViewById(R.id.tv_content);
  mToolbar = (Toolbar) mView.findViewById(R.id.toolbar);
  sv.setVisibility(View.VISIBLE);
  wv_doc.setVisibility(View.INVISIBLE);
  ((AppCompatActivity) getActivity()).setSupportActionBar(mToolbar);
  }

  private void initData() {
  Bundle bundle = getArguments();
  int position = bundle.getInt("position");
  mView.setTag(new Integer(position));
  mData = DocumentAdapter.mValues.get(position);
  tv_title.setText(mData.getTitle());
  tv_unit.setText(mData.getUnit() + " " + mData.getTime());
  tv_content.setText(mData.getContent());
  }

  private void showWebView() {
  hasLoad = true;
  //展示原网页
  WebSettings settings = wv_doc.getSettings();
  settings.setJavaScriptEnabled(true);
  settings.setBuiltInZoomControls(true);
  settings.setUseWideViewPort(true);

  wv_doc.setWebViewClient(new WebViewClient() {
      @Override
      public boolean shouldOverrideUrlLoading(WebView view, String url) {
          view.loadUrl(url);
          return true;
      }
  });
  
  wv_doc.setWebChromeClient(new WebChromeClient() {
  
      @Override
      public void onProgressChanged(WebView view, int newProgress) {
          super.onProgressChanged(view, newProgress);
      }
  
      @Override
      public void onReceivedTitle(WebView view, String title) {
          super.onReceivedTitle(view, title);
      }
  });
  wv_doc.loadUrl(mData.getUrl());
  

  }

  @Override
  public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
  inflater.inflate(R.menu.menu_main, menu);
  super.onCreateOptionsMenu(menu, inflater);
  }

  @Override
  public boolean onOptionsItemSelected(MenuItem item) {
  int id = item.getItemId();
  if (id == R.id.action_settings) {
  if (!isWebView) {
  if (!hasLoad)
  showWebView();
  wv_doc.setVisibility(View.VISIBLE);
  sv.setVisibility(View.INVISIBLE);
  } else {
  wv_doc.setVisibility(View.INVISIBLE);
  sv.setVisibility(View.VISIBLE);
  }
  isWebView = !isWebView;
  item.setTitle(isWebView ? "返回" : "查看原网页");
  return true;
  }
  return super.onOptionsItemSelected(item);
  }
  }
  package com.testing.simplesp.adapter.Document;

import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentStatePagerAdapter;

import com.testing.simplesp.fragment.DocumentDetailFragment;

/**

• Created by admin on 2016/7/12.
  */
  public class DocumentDetailPageAdapter extends FragmentStatePagerAdapter {
  public DocumentDetailPageAdapter(FragmentManager fm) {
  super(fm);
  }

  @Override
  public Fragment getItem(int position) {
  System.out.println(position);
  return DocumentDetailFragment.newInstance(position);
  }

  @Override
  public int getCount() {
  return DocumentAdapter.mValues.size();
  }

}
package com.testing.simplesp.activity;

import android.os.Bundle;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.webkit.WebView;
import android.widget.ScrollView;
import android.widget.TextView;

import com.testing.simplesp.R;
import com.testing.simplesp.adapter.Document.DocumentDetailPageAdapter;
import com.testing.simplesp.domain.DocumentItem.Data;

public class DocumentDetailActivity extends AppCompatActivity {

public static ViewPager sViewPager;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    initView();
    initData();

}


private void initData() {
    //不展示原网页

    setTitle("校园公文通");

}


private void initView() {
    setContentView(R.layout.activity_detail_document);
    sViewPager = (ViewPager) findViewById(R.id.container);
    int position = getIntent().getIntExtra("currentPosition", 0);
    sViewPager.setAdapter(new DocumentDetailPageAdapter(getSupportFragmentManager()));
    sViewPager.setCurrentItem(position);

}

}

很奇怪的是，第一个fragment点击menuitme的时候，webview左右是无法拖动的，但是其他界面却可以。
还有
当position = 0时，position=1的menuitem是不显示的，但是滑动到第四个fragment再滑动回来却有显示。
当postion>0时，position-1的显示情况和上述一模一样。

找了各个地方，实在是找不到哪里出了问题。求助！！！

Answer 1

https://www.baidu.com/link?url=sTPvJ_v9br78Em3iBQw6WNWwWI4YpKnIh2VAzuExBUSjBwnkGVgujGQWF7HV4DASuJs9HHl0-NmtdL705j4HJjZA_S7o3T26AQGFx6uLHLO&wd=&eqid=bb5c26ea0007242f0000000558c416af