Web视图片段调用问题

Question

该应用程序有三个活动，第二个包含6个带View Viewr的Web视图片段，我不想在按下后退按钮时返回上一个活动，但只需返回一个页面。我必须调用相关活动中的片段我知道，但我无法弄清楚代码无法正常工作的原因，当我转到应用程序崩溃的第二个活动时，这里是代码。任何专家？感谢

Web视图片段代码。

    package com.example.AzaaadCompany.mymessenger;

import android.os.Bundle;    
import android.support.annotation.Nullable;    
import android.support.v4.app.Fragment;    
import android.view.LayoutInflater;    
import android.view.View;    
import android.view.ViewGroup;    
import android.webkit.WebChromeClient;    
import android.webkit.WebSettings;    
import android.webkit.WebView;    
import android.webkit.WebViewClient;      

public class Fragment1 extends Fragment {    
    public Fragment1() {
        }

    @Nullable       
    @Override    

    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {

        View rootView = inflater.inflate(R.layout.fragment_layout, container, false);

        final WebView web = (WebView) rootView.findViewById(R.id.webView);
        WebSettings webSettings = web.getSettings();
        webSettings.setJavaScriptEnabled(true);
        web.setLayerType(View.LAYER_TYPE_HARDWARE, null);
        web.getSettings().setCacheMode(webSettings.LOAD_CACHE_ELSE_NETWORK);
        web.getSettings().setRenderPriority(WebSettings.RenderPriority.HIGH);
        web.getSettings().setAppCacheEnabled(true);
        webSettings.setDomStorageEnabled(true);
        webSettings.setLayoutAlgorithm(WebSettings.LayoutAlgorithm.NARROW_COLUMNS);
        webSettings.setUseWideViewPort(true);
        webSettings.setSaveFormData(true);
        webSettings.setEnableSmoothTransition(true);
        webSettings.setSupportZoom(true);
        webSettings.setBuiltInZoomControls(true);
        webSettings.setDisplayZoomControls(true);
        web.setInitialScale(228);
        web.loadUrl("http://allrecipes.com/");
        web.setWebChromeClient(new WebChromeClient());
        web.setWebViewClient(new WebViewClient1());
        return rootView;
    }

    private class WebViewClient1 extends WebViewClient {
            @Override
            public boolean shouldOverrideUrlLoading(WebView view, String url) {
                view.loadUrl(url);
                return true;
           }
       }

活动代码

package com.example.AzaaadCompany.mymessenger;      

import android.content.Context;    
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.HorizontalScrollView;
import android.widget.TabHost;
import java.util.ArrayList;    
import java.util.List;

public class secondActivity extends AppCompatActivity implements 

ViewPager.OnPageChangeListener,TabHost.OnTabChangeListener {
    ViewPager viewPager;
    TabHost tabHost;

   android.support.v4.app.FragmentManager manager;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_second);

        ReplaceFont.replaceDefaultFont(this, "DEFAULT", "birds.ttf");
        manager=getSupportFragmentManager();
        android.support.v4.app.FragmentTransaction ft= manager.beginTransaction();
        Fragment1 f1= new Fragment1();
        ft.add(R.id.webView,f1);
        ft.addToBackStack(null);
        ft.commit();
       initviewpager();
        initTabHost();

      }
    private void initTabHost() {
        tabHost = (TabHost) findViewById(R.id.tabHost);
        tabHost.setup();

        String[] tabNames = {"allrecipes", "zoomit", "p30download", "microsoft", "walmart", "amazon"};

        for (int i = 0; i < tabNames.length; i++)    
        {
            TabHost.TabSpec tabSpec;
            tabSpec = tabHost.newTabSpec(tabNames[i]);
            tabSpec.setIndicator(tabNames[i]);
            tabSpec.setContent(new FakeContent(getApplicationContext()));
            tabHost.addTab(tabSpec);
        }
        tabHost.setOnTabChangedListener(this);
    }
    @Override
    public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

    }
    @Override
    public void onPageSelected(int selectedItem) {
        tabHost.setCurrentTab(selectedItem);
    }
    @Override
    public void onPageScrollStateChanged(int state) {

    }
    @Override
    public void onTabChanged(String tabId) {
        int selectedItem = tabHost.getCurrentTab();
        viewPager.setCurrentItem(selectedItem);

        HorizontalScrollView horizontalScrollView = (HorizontalScrollView) findViewById(R.id.myscrollview);

        View tabView = tabHost.getCurrentTabView();
        int scrollpos = tabView.getLeft() - (horizontalScrollView.getWidth() - tabView.getWidth()) / 2;

        horizontalScrollView.smoothScrollTo(scrollpos, 0);

           }
    public class FakeContent implements TabHost.TabContentFactory {
        Context context;

        public FakeContent(Context mcontext) {
            context = mcontext;
        }
        @Override
        public View createTabContent(String tag) {
            View fakeView = new View(context);

            fakeView.setMinimumHeight(0);
            fakeView.setMinimumWidth(0);

            return fakeView;
        }
    }
    private void initviewpager() {
        viewPager = (ViewPager) findViewById(R.id.view_pager);
        List<Fragment> listFragments = new ArrayList<Fragment>();

        listFragments.add(new Fragment1());
        listFragments.add(new Fragment2());
        listFragments.add(new Fragment3());
        listFragments.add(new Fragment4());
        listFragments.add(new Fragment5());
        listFragments.add(new Fragment6());

        MyFragmentPagerAdapter myFragmentPagerAdapter = new MyFragmentPagerAdapter(getSupportFragmentManager(), listFragments);

        viewPager.setAdapter(myFragmentPagerAdapter);
        viewPager.setOnPageChangeListener(this);
    }
    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.my_menu, menu);
        return true;
    }
    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        return super.onOptionsItemSelected(item);
    }
}