当我将应用程序推回到背景,点击后退或主页按钮,它在“缓存的后台进程”中使用大约40MB,我不明白为什么.

这是我的一个Webview的一个例子：

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.RelativeLayout;

public class Presentation extends Fragment {
    boolean isOption = false;
    RelativeLayout main = null;
    WebView web_main = null;

    public Presentation () {

    }

    @Override
    public View onCreateView(LayoutInflater inflater,ViewGroup container,Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        main = (RelativeLayout) inflater.inflate(R.layout.webview,container,false);
        return main;

    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onActivityCreated(savedInstanceState);
        web_main = new WebView(getActivity().getApplicationContext());
        web_main.setWebViewClient(new WebViewClient());
        web_main.getSettings().setAppCacheEnabled(false);
        web_main.loadUrl("file:///android_asset/main.html");
        main.removeAllViews();
        main.addView(web_main);
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        Log.i(getClass().getName(),"[OnDestroy]");
        main.removeAllViews();
        web_main.destroy();
        main = null;
        web_main = null;
        System.gc();
    }

}

我遵循几个教程和答案,但对缓存后台进程没有任何影响
这是我的主要活动：

public class AppTest extends FragmentActivity {

/**
 * The {@link android.support.v4.view.PagerAdapter} that will provide
 * fragments for each of the sections. We use a
 * {@link android.support.v4.app.FragmentPagerAdapter} derivative,which
 * will keep every loaded fragment in memory. If this becomes too memory
 * intensive,it may be best to switch to a
 * {@link android.support.v4.app.FragmentStatePagerAdapter}.
 */
SectionsPagerAdapter mSectionsPagerAdapter;

/**
 * The {@link ViewPager} that will host the section contents.
 */
ViewPager mViewPager;

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

    // Create the adapter that will return a fragment for each of the three
    // primary sections of the app.
    mSectionsPagerAdapter = new SectionsPagerAdapter(
            getSupportFragmentManager());

    // Set up the ViewPager with the sections adapter.
    mViewPager = (ViewPager) findViewById(R.id.pager);
    mViewPager.setAdapter(mSectionsPagerAdapter);

}

@Override
protected void onStop() {
    super.onStop();
    System.gc();
    Log.i(getClass().getName(),"[OnStop]");
    android.os.Debug.stopMethodTracing();

}


@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main_content,menu);
    return true;
}

@Override
protected void onDestroy() {
    super.onDestroy();
    mViewPager.removeAllViews();
    Log.i(getClass().getName(),"[OnDestroy]");
}

/**
 * A {@link FragmentPagerAdapter} that returns a fragment corresponding to
 * one of the sections/tabs/pages.
 */
public class SectionsPagerAdapter extends FragmentStatePagerAdapter {

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

    @Override
    public Fragment getItem(int position) {
        // getItem is called to instantiate the fragment for the given page.
        // Return a DummySectionFragment (defined as a static inner class
        // below) with the page number as its lone argument.
        Fragment fragment = null;

        switch (position) {
        case 0:
            fragment = new Presentation();
            break;
              /*    case 1:
            fragment = new Edition();
            break;
        case 2:
            fragment = new Programme();
            break;
        case 3:
            fragment = new Twitter();
            break;
        case 4:
            fragment = new Partenaire();
            break;
        case 5:
            fragment = new Information();
            break;*/
        default:
            fragment = new Presentation();
            break;
        }


        return fragment;
    }

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

    @Override
    public CharSequence getPageTitle(int position) {

        switch (position) {
        case 0:
            return "Presentation";
        case 1:
            return "Edition";
        case 2:
            return "Program";
        case 3:
            return "Tweets";
        case 4:
            return "Partners";
        case 5:
            return "Information";
        }
        return null;
    }
}
}

谁能看到有什么错误？

编辑
我试图把webview放在布局中,但是它仍然是一样的
其实我想知道当应用程序处于后台状态时缓存中放置什么？