首先建立一個抽象類BackHandledFragment，該類有一個抽象方法onBackPressed()，所有BackHandledFragment的子類在onBackPressed方法中處理各自對Back事件的消費邏輯。onBackPressed返回布林值，宿主Activity將會根據該方法的返回值判斷子Fragment是否有消費Back事件。此外，宿主FragmentActivity還會保持一份當前Fragment的引用，當用戶按下Back鍵時，宿主Activity會判斷當前Fragment是否需要消費該事件，如果沒有Fragment消費才會自己消費。

public abstract class BackHandledFragment extends Fragment{

    protected BackHandledInterface mBackHandledInterface;

    /**
     * 所有繼承BackHandledFragment的子類都將在這個方法中實現物理Back鍵按下後的邏輯
     * FragmentActivity捕捉到物理返回鍵點選事件後會首先詢問Fragment是否消費該事件
     * 如果沒有Fragment訊息時FragmentActivity自己才會消費該事件
     */
    public abstract boolean onBackPressed();

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if(!(getActivity() instanceof BackHandledInterface)){
            throw new ClassCastException("Hosting Activity must implement BackHandledInterface");
        }else{
            this.mBackHandledInterface = (BackHandledInterface)getActivity();
        }
    }

    @Override
    public void onStart() {
        super.onStart();
        //告訴FragmentActivity，當前Fragment在棧頂
        mBackHandledInterface.setSelectedFragment(this);
    }
}
 

public interface BackHandledInterface {
    void setSelectedFragment(BackHandledFragment selectedFragment);
}

public class MainActivity extends FragmentActivity implements BackHandledInterface{

	private BackHandledFragment mBackHandedFragment;
	private boolean hadIntercept;

	@Override
	public void setSelectedFragment(BackHandledFragment selectedFragment) {
		this.mBackHandedFragment = selectedFragment;
	}
	
	@Override
	public void onBackPressed() {
		if(mBackHandedFragment == null || !mBackHandedFragment.onBackPressed()){
			if(getSupportFragmentManager().getBackStackEntryCount() == 0){
				super.onBackPressed(); //退出
			}else{
				getSupportFragmentManager().popBackStack(); //fragment 出棧
			}
		}
	}
}
 

public class WorkFragment extends BackHandledFragment {

    private WebView webView;
    private WebSettings webSettings;

    private String url = "https://www.baidu.com/";
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

        View view = inflater.inflate(R.layout.work_fragment,container,false);
        webView = (WebView)view.findViewById(R.id.workWebView);

        webSettings = webView.getSettings();
        webSettings.setJavaScriptEnabled(true);
        webSettings.setUseWideViewPort(true);
        webSettings.setLoadWithOverviewMode(true);

        webView.setWebViewClient(new MyWebViewClient());
        webView.loadUrl(url);

        return view;
    }

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

        @Override
        public void onReceivedError(WebView view, int errorCode,
                                    String description, String failingUrl) {
            //     super.onReceivedError(view, errorCode, description, failingUrl);
            //  Toast.makeText(this,"網頁載入錯誤！",0).show();
        }
    }
    @Override
    public  boolean onBackPressed(){

        if(webView.canGoBack()){
            webView.goBack();
            Log.v("webView.goBack()", "webView.goBack()");
            return true;

        }else{
            Log.v("Conversatio退出","Conversatio退出");
            return false;
        }

    }

}