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我正在尝试对我的片段选项卡实施检查 Internet 连接。它似乎没有运行。任何人都可以检查我的代码。我希望我的应用程序在加载片段选项卡之前检查互联网连接。 

public class FreeFragment extends SherlockListFragment implements
        ActionBar.TabListener {

    static final String URL = "https://myxml.xml";
    static final String KEY_SONG = "song";
    static final String KEY_ID = "id";
    static final String KEY_TITLE = "title";
    static final String KEY_CAT_ARTIST = "artistcat";
    static final String KEY_DURATION = "duration";
    static final String KEY_THUMB_URL = "thumb_url";
    static final String KEY_BIG_URL = "big_url";
    static final String KEY_CAT_URL = "cat_url";
    static final String KEY_DESC = "cat_desc";
    ArrayList<HashMap<String, String>> menuItems;
    ListAdapter adapter;
    Context appContext;
    private Fragment mFragment;

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {

        checkInternetConnection();

        super.onActivityCreated(savedInstanceState);
    }




    public class loadListView extends AsyncTask<Integer, String, String> {

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
        }

        @Override
        protected String doInBackground(Integer... args) {
            // updating UI from Background Thread
            menuItems = new ArrayList<HashMap<String, String>>();

            XMLParser parser = new XMLParser();
            String xml = parser.getXmlFromUrl(URL); // getting XML
            Document doc = parser.getDomElement(xml); // getting DOM element

            NodeList nl = doc.getElementsByTagName(KEY_SONG);
            // looping through all item nodes <item>
            for (int i = 0; i < nl.getLength(); i++) {
                // creating new HashMap
                HashMap<String, String> map = new HashMap<String, String>();
                Element e = (Element) nl.item(i);
                // adding each child node to HashMap key => value
                map.put(KEY_ID, parser.getValue(e, KEY_ID));
                map.put(KEY_TITLE, parser.getValue(e, KEY_TITLE));
                map.put(KEY_CAT_ARTIST, parser.getValue(e, KEY_CAT_ARTIST));
                map.put(KEY_DURATION, parser.getValue(e, KEY_DURATION));
                map.put(KEY_THUMB_URL, parser.getValue(e, KEY_THUMB_URL));
                map.put(KEY_BIG_URL, parser.getValue(e, KEY_BIG_URL));
                map.put(KEY_CAT_URL, parser.getValue(e, KEY_CAT_URL));
                map.put(KEY_DESC, parser.getValue(e, KEY_DESC));
                // adding HashList to ArrayList
                menuItems.add(map);
            }
            return null;
        }

        @Override
        protected void onPostExecute(String args) {

            if (getActivity() != null) {
                adapter = new MainPageLazyAdapter(getActivity(), menuItems);
                setListAdapter(adapter);

                ListView lv = getListView();

                lv.setOnItemClickListener(new OnItemClickListener() {

                    @Override
                    public void onItemClick(AdapterView<?> parent, View view,
                            int position, long id) {
                        String thumburl;
                        String bigurl;
                        String caturl;
                        String title;
                        String desc;
                        String artist;
                        Intent in;

                        title = ((TextView) view.findViewById(R.id.title))
                                .getText().toString();
                        artist = ((TextView) view.findViewById(R.id.artist))
                                .getText().toString();
                        desc = ((TextView) view.findViewById(R.id.desc))
                                .getText().toString();
                        thumburl = ((TextView) view
                                .findViewById(R.id.thumb_image)).getText()
                                .toString();
                        caturl = ((TextView) view.findViewById(R.id.cat))
                                .getText().toString();
                        bigurl = ((TextView) view.findViewById(R.id.big_image))
                                .getText().toString();

                        in = new Intent(getActivity(),
                                SingleImageViewActivity.class);

                        in.putExtra(KEY_TITLE, title);
                        in.putExtra(KEY_DESC, desc);
                        in.putExtra(KEY_CAT_URL, caturl);
                        in.putExtra(KEY_THUMB_URL, thumburl);
                        in.putExtra(KEY_BIG_URL, bigurl);
                        in.putExtra(KEY_CAT_ARTIST, artist);
                        startActivity(in);

                    }
                });
            }

        }
    }

    private boolean checkInternetConnection() {
        ConnectivityManager cm = (ConnectivityManager) appContext.getSystemService(Context.CONNECTIVITY_SERVICE);
        // test for connection
        if (cm.getActiveNetworkInfo() != null
                && cm.getActiveNetworkInfo().isAvailable()
                && cm.getActiveNetworkInfo().isConnected()) {
            new loadListView().execute();
            return true;
        } else {
            Toast.makeText(appContext, "Internet Connection Required" , Toast.LENGTH_LONG).show();


            AlertDialog.Builder builder = new AlertDialog.Builder(appContext);
             builder.setMessage("Internet Connection Required")
                    .setCancelable(false)
                    .setPositiveButton("Exit", new DialogInterface.OnClickListener() {
                        public void onClick(DialogInterface dialog, int id) {
                            System.exit(0);
                        }

                       });
            AlertDialog alert = builder.create();
             alert.show(); 

                 }

        return false;
     }

    @Override
    public void onTabSelected(Tab tab, FragmentTransaction ft) {
        mFragment = new FreeFragment();
        ft.add(android.R.id.content, mFragment);
        ft.attach(mFragment);
    }

    @Override
    public void onTabUnselected(Tab tab, FragmentTransaction ft) {
        ft.remove(mFragment);
    }

    @Override
    public void onTabReselected(Tab tab, FragmentTransaction ft) {

    }
}

日志猫：

11-01 17:06:30.585: E/AndroidRuntime(28090): FATAL EXCEPTION: main
11-01 17:06:30.585: E/AndroidRuntime(28090): java.lang.RuntimeException: Unable to start activity ComponentInfo{in.wptrafficanalyzer.actionbarsherlocknavtab/in.wptrafficanalyzer.actionbarsherlocknavtab.MainActivity}: java.lang.NullPointerException
11-01 17:06:30.585: E/AndroidRuntime(28090):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1651)
11-01 17:06:30.585: E/AndroidRuntime(28090):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1667)
11-01 17:06:30.585: E/AndroidRuntime(28090):    at android.app.ActivityThread.access$1500(ActivityThread.java:117)
11-01 17:06:30.585: E/AndroidRuntime(28090):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:935)
11-01 17:06:30.585: E/AndroidRuntime(28090):    at android.os.Handler.dispatchMessage(Handler.java:99)
11-01 17:06:30.585: E/AndroidRuntime(28090):    at android.os.Looper.loop(Looper.java:130)
11-01 17:06:30.585: E/AndroidRuntime(28090):    at android.app.ActivityThread.main(ActivityThread.java:3691)
11-01 17:06:30.585: E/AndroidRuntime(28090):    at java.lang.reflect.Method.invokeNative(Native Method)
11-01 17:06:30.585: E/AndroidRuntime(28090):    at java.lang.reflect.Method.invoke(Method.java:507)
11-01 17:06:30.585: E/AndroidRuntime(28090):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:907)
11-01 17:06:30.585: E/AndroidRuntime(28090):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:665)
11-01 17:06:30.585: E/AndroidRuntime(28090):    at dalvik.system.NativeStart.main(Native Method)
11-01 17:06:30.585: E/AndroidRuntime(28090): Caused by: java.lang.NullPointerException
11-01 17:06:30.585: E/AndroidRuntime(28090):    at in.wptrafficanalyzer.actionbarsherlocknavtab.FreeFragment.checkInternetConnection(FreeFragment.java:151)
11-01 17:06:30.585: E/AndroidRuntime(28090):    at in.wptrafficanalyzer.actionbarsherlocknavtab.FreeFragment.onActivityCreated(FreeFragment.java:51)
11-01 17:06:30.585: E/AndroidRuntime(28090):    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:891)
11-01 17:06:30.585: E/AndroidRuntime(28090):    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1080)
11-01 17:06:30.585: E/AndroidRuntime(28090):    at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:622)
11-01 17:06:30.585: E/AndroidRuntime(28090):    at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1416)
11-01 17:06:30.585: E/AndroidRuntime(28090):    at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:505)
11-01 17:06:30.585: E/AndroidRuntime(28090):    at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1129)
11-01 17:06:30.585: E/AndroidRuntime(28090):    at android.app.Activity.performStart(Activity.java:3817)
11-01 17:06:30.585: E/AndroidRuntime(28090):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1624)
11-01 17:06:30.585: E/AndroidRuntime(28090):    ... 11 more
4

1 回答 1

1

你的xml中的问题。

   String xml = parser.getXmlFromUrl(URL); // getting XML
   Document doc = parser.getDomElement(xml); // getting DOM element

修复此代码，它应该可以工作。

// check internet connection
public class MainActivity extends FragmentActivity {

    Fragment1 fragment1 = new Fragment1();

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if(!checkInternet()){
            // show error View
        }
        setContentView(R.layout.activity_main);     
    }
}
于 2012-11-01T08:54:48.363 回答