WebViewFragment webView is null after doing a Frag

问题:

I currently have my application set up with a ListFragment on the left and a DetailsFragment on the right (similar to the layout on the tablet below).

On the details fragment (fragment next to the list) I have a goto deal button, which when pressed should replace the detailsFragment with a WebViewFragment.

The problem I am having is that when trying to load a url in the webviewfragment the WebView is null.

WebViewFragment webViewFragment = new WebViewFragment();

FragmentTransaction transaction = getFragmentManager().beginTransaction();

// Replace whatever is in the fragment_container view with this fragment,
// and add the transaction to the back stack
transaction.replace(R.id.deal_details_fragment, webViewFragment);
transaction.addToBackStack(null);

// Commit the transaction
transaction.commit();

// Set the url
if (webViewFragment.getWebView()==null)
    Log.d("webviewfragment", "is null");
webViewFragment.getWebView().loadUrl("http://www.google.com");

Below is my main layout which has the original two fragments defined.

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
          android:id="@+id/main_activity_layout"

    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="horizontal" >

  <fragment
      android:name="com.bencallis.dealpad.DealListFragment"
      android:id="@+id/deal_list_fragment"
      android:layout_weight="1"
      android:layout_width="0px"
      android:layout_height="match_parent" >
      <!-- Preview: layout=@layout/deal_list_fragment -->
  </fragment>
  <fragment
      android:name="com.bencallis.dealpad.DealDetailsFragment"
      android:id="@+id/deal_details_fragment"
      android:layout_weight="2"
      android:layout_width="0px"
      android:layout_height="match_parent" >
      <!-- Preview: layout=@layout/deal_details_fragment -->
  </fragment>

</LinearLayout>

It seems that the webViewFragment is not being created fully as the WebView has not been initialised. I have looked online but there is very little information regarding the WebViewFragment.

Any ideas how to ensure WebView is initialised in the WebViewFragment?

回答1:

With great help from Espiandev I have managed to get a working WebView. To ensure that links opened in the fragment and not in a web browser application I created a simple InnerWebView client which extends WebViewClinet.

public class DealWebViewFragment extends Fragment {

    private WebView mWebView;
    private boolean mIsWebViewAvailable;
    private String mUrl = null;

    /**
     * Creates a new fragment which loads the supplied url as soon as it can
     * @param url the url to load once initialised
     */
    public DealWebViewFragment(String url) {
        super();
        mUrl = url;
    }

    /**
     * Called to instantiate the view. Creates and returns the WebView.
     */
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {

        if (mWebView != null) {
            mWebView.destroy();
        }
        mWebView = new WebView(getActivity());
        mWebView.setOnKeyListener(new OnKeyListener(){


            @Override
            public boolean onKey(View v, int keyCode, KeyEvent event) {
                  if ((keyCode == KeyEvent.KEYCODE_BACK) && mWebView.canGoBack()) {
                        mWebView.goBack();
                        return true;
                    }
                    return false;
            }

        });
        mWebView.setWebViewClient(new InnerWebViewClient()); // forces it to open in app
        mWebView.loadUrl(mUrl);
        mIsWebViewAvailable = true;
        WebSettings settings = mWebView.getSettings();
        settings.setJavaScriptEnabled(true);
        return mWebView;
    }

    /**
     * Convenience method for loading a url. Will fail if {@link View} is not initialised (but won't throw an {@link Exception})
     * @param url
     */
    public void loadUrl(String url) {
        if (mIsWebViewAvailable) getWebView().loadUrl(mUrl = url);
        else Log.w("ImprovedWebViewFragment", "WebView cannot be found. Check the view and fragment have been loaded.");
    }

    /**
     * Called when the fragment is visible to the user and actively running. Resumes the WebView.
     */
    @Override
    public void onPause() {
        super.onPause();
        mWebView.onPause();
    }

    /**
     * Called when the fragment is no longer resumed. Pauses the WebView.
     */
    @Override
    public void onResume() {
        mWebView.onResume();
        super.onResume();
    }

    /**
     * Called when the WebView has been detached from the fragment.
     * The WebView is no longer available after this time.
     */
    @Override
    public void onDestroyView() {
        mIsWebViewAvailable = false;
        super.onDestroyView();
    }

    /**
     * Called when the fragment is no longer in use. Destroys the internal state of the WebView.
     */
    @Override
    public void onDestroy() {
        if (mWebView != null) {
            mWebView.destroy();
            mWebView = null;
        }
        super.onDestroy();
    }

    /**
     * Gets the WebView.
     */
    public WebView getWebView() {
        return mIsWebViewAvailable ? mWebView : null;
    }

    /* To ensure links open within the application */
    private class InnerWebViewClient extends WebViewClient {
        @Override
        public boolean shouldOverrideUrlLoading(WebView view, String url) {
            view.loadUrl(url);
            return true;
        }


    }

Hopefully this is useful to someone in the future.

回答2:

EDIT: So I played around with this for a while and it seems that the WVF is a bit rubbish and designed to be overridden. However, there's no documentation on this at all! The problem stems from the fact you can call getWebView() before the Fragments view is loaded, hence your NullPointerException. Except there isn't any way to detect when the Fragment's view has been loaded, so you're kind of stuck!

Instead I overrode the class, adding bits and changing bits, so that now it will work fine. Check this link for the code. Then instead of using:

WebViewFragment webViewFragment = new WebViewFragment();

to load your Fragment, use:

ImprovedWebViewFragment wvf = new ImprovedWebViewFragment("www.google.com");

This class also includes a convenience method for loading a url, that won't throw an Exception if there's no WebView.

So, no, I don't think there's a particularly simple way for using the built-in WebViewFragment, but it is pretty easy to make something that works instead. Hope it helps!

回答3:

WebViewFragment as is is not that straightforward to use. Try this simple extension (You can copy/paste):

public class UrlWebViewFragment extends WebViewFragment{

    private String url;

    public static UrlWebViewFragment newInstance(String url) {
        UrlWebViewFragment fragment = new UrlWebViewFragment();
        fragment.url = url;
        return fragment;
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        WebView webView = (WebView) super.onCreateView(inflater, container, savedInstanceState);
        webView.loadUrl(url);
        return webView;
    }         
  }

Call where you need using the factory method:

WebViewFragment fragment = UrlWebViewFragment.newInstance("http://ur-url.com");

回答4:

Fragments can only be replaced if they were initiallized in Java, not XML. I think so, I had the same problem and it solved it. Change your XML to this:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
          android:id="@+id/main_activity_layout"

    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="horizontal" >

  <fragment
      android:name="com.bencallis.dealpad.DealListFragment"
      android:id="@+id/deal_list_fragment"
      android:layout_weight="1"
      android:layout_width="0px"
      android:layout_height="match_parent" >
      <!-- Preview: layout=@layout/deal_list_fragment -->
  </fragment>
  <View
      android:id="@+id/my_container"
      android:layout_weight="2"
      android:layout_width="0px"
      android:layout_height="match_parent" >
  </View>

</LinearLayout>

and then in Java, your onCreate method:

FragmentTransaction transaction = getFragmentManager().beginTransaction();
transaction.replace(R.id.my_container, new DealDetailsFragment());
transaction.commit();

or even better create whole method to just deal with Transactions.

Now Transaction from your question should work. :)