WebView片段上的“后退”按钮-不会转到上一页

Question

我在Fragments中有WebView，在一个Fragment中只有一些按钮（不是WebView）。当按下“后退按钮”时，我打算返回WebView的上一页（其余部分，或者当没有上一页时，关闭该应用程序就可以了）。在这里经过几个建议之后，我终于想到了这一点，但是它并没有导致按下返回按钮的上一页。

我不确定是否与Stack Overflow post中的addToBackStack有关；我也不确定如何在我的情况下进行该工作。

public class MyFragment extends Fragment {


    public WebView webView;

    public boolean WebViewGoBack() {
        if(webView.canGoBack()){
            webView.goBack();
            return true;
        }
        return false; //webview cannot go back, so use the method of the BackButton
    }


}

一个片段是这样实现的：

public class Tab1Fb extends MyFragment  {




    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.tab1fb, container, false);


        webView =(WebView)rootView.findViewById(R.id.webView);

        webView.setWebViewClient(new WebViewClient());
        webView.getSettings().setJavaScriptEnabled(true);
        webView.getSettings().setDomStorageEnabled(true);
        webView.setOverScrollMode(WebView.OVER_SCROLL_NEVER);
        webView.loadUrl("https://www.facebook.com/");


        return rootView;
    }






}

MainActivity，我有pageradapter和重写的方法：

public class SectionsPagerAdapter extends FragmentPagerAdapter {

    private Fragment mCurrentFragment;

    public SectionsPagerAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public Fragment getItem(int position) {

        switch (position) {
            case 0:
                Tab1Fb tab1 = new Tab1Fb();
                return tab1;

            case 1:
                Tab2Videos tab2 = new Tab2Videos();
                return tab2;

            case 2:
                Tab3Downloads tab3 = new Tab3Downloads();
                return tab3;

            case 3:
                Tab4Twitter tab4 = new Tab4Twitter();
                return tab4;

            case 4:
                Tab5Contact tab5 = new Tab5Contact();
                return tab5;

            case 5:
                Tab6Support tab6 = new Tab6Support();
                return tab6;

            default:
                return null;

        }
    }

    @Override
    public int getCount() {
        // Show 3 total pages.
        return 6;
    }


    @Override
    public CharSequence getPageTitle(int position) {

        switch (position) {
            case 0:
                return "FACEBOOK";
            case 1:
                return "VIDEOS";
            case 2:
                return "DOWNLOADS";
            case 3:
                return "TWITTER";
            case 4:
                return "CONTACT";
            case 5:
                return "JOIN";

        }

        return null;
    }


    public Fragment getCurrentFragment() {
        return mCurrentFragment;
    }

    @Override
    public void setPrimaryItem(View container, int position, Object object) {
        if (getCurrentFragment() != object) {
            mCurrentFragment = ((Fragment) object);
        }
        super.setPrimaryItem(container, position, object);
    }




}


@Override
public void onBackPressed() {
    switch (mViewPager.getCurrentItem()) {
        case 0:
            if (!webViewGoBack(0)) {
                //do something if webview cannot go back
            }
            break;
        case 1:

            break;
        default:
    }
}



public boolean webViewGoBack(int num) {
    SectionsPagerAdapter adapter = ((SectionsPagerAdapter)mViewPager.getAdapter());

    MyFragment f = (MyFragment )adapter.getCurrentFragment();

    if (f!= null) {
        return f.WebViewGoBack();

    }
    return false;
}