Xml 正在解析 activity 如果没有连接则强制关闭

Question

我正在使用教程中的以下代码，代码运行良好，但如果没有连接或连接速度慢，应用程序将强制关闭。

public class MainActivity extends Activity {

    ListView mListView;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // URL to the XML data
        String strUrl = "http://wptrafficanalyzer.in/p/demo1/countries_xml.php/countries/";

        // Creating a new non-ui thread task to download xml data
        DownloadTask downloadTask = new DownloadTask();

        // Starting the download process
        downloadTask.execute(strUrl);

        // Getting a reference to ListView of activity_main
        mListView = (ListView) findViewById(R.id.lv_countries);

    }

    /** A method to download xml data from url */
    private String downloadUrl(String strUrl) throws IOException{
        String data = "";
        InputStream iStream = null;
        try{
            URL url = new URL(strUrl);

            // Creating an http connection to communicate with url
            HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();

            // Connecting to url
            urlConnection.connect();

            // Reading data from url
            iStream = urlConnection.getInputStream();

            BufferedReader br = new BufferedReader(new InputStreamReader(iStream));

            StringBuffer sb  = new StringBuffer();

            String line = "";
            while( ( line = br.readLine())  != null){
                sb.append(line);
            }

            data = sb.toString();

            br.close();

        }catch(Exception e){
            Log.d("Exception while downloading url", e.toString());
        }finally{
            iStream.close();
        }
        return data;
    }

    /** AsyncTask to download xml data */
    private class DownloadTask extends AsyncTask<String, Integer, String>{
        String data = null;
        @Override
        protected String doInBackground(String... url) {
            try{
                data = downloadUrl(url[0]);
            }catch(Exception e){
                Log.d("Background Task",e.toString());
            }
            return data;
        }

        @Override
        protected void onPostExecute(String result) {

            // The parsing of xml data is done in a non-ui thread
            ListViewLoaderTask listViewLoaderTask = new ListViewLoaderTask();

            // Start parsing xml data
            listViewLoaderTask.execute(result);
        }
    }

    /** AsyncTask to parse xml data and load ListView */
    private class ListViewLoaderTask extends AsyncTask<String, Void, SimpleAdapter>{

        StringReader reader;

        // Doing the parsing of xml data in a non-ui thread
        @Override
        protected SimpleAdapter doInBackground(String... strXml) {
            try{
                reader = new StringReader(strXml[0]);
            }catch(Exception e){
                Log.d("XML Exception1",e.toString());
            }

            // Instantiating xml parser class
            CountryXmlParser countryXmlParser = new CountryXmlParser();

            // A list object to store the parsed countries list
            List<HashMap<String, Object>> countries = null;

            try{
                // Getting the parsed data as a List construct
                countries = countryXmlParser.parse(reader);
            }catch(Exception e){
                Log.d("Exception",e.toString());
            }

            // Keys used in Hashmap
            String[] from = { "country","flag","details"};

            // Ids of views in listview_layout
            int[] to = { R.id.tv_country,R.id.iv_flag,R.id.tv_country_details};

            // Instantiating an adapter to store each items
            // R.layout.listview_layout defines the layout of each item
            SimpleAdapter adapter = new SimpleAdapter(getBaseContext(), countries, R.layout.lv_layout, from, to);

            return adapter;
        }

        /** Invoked by the Android when "doInBackground" is executed */
        @Override
        protected void onPostExecute(SimpleAdapter adapter) {

            // Setting adapter for the listview
            mListView.setAdapter(adapter);

            for(int i=0;i<adapter.getCount();i++){
                HashMap<String, Object> hm = (HashMap<String, Object>) adapter.getItem(i);
                String imgUrl = (String) hm.get("flag_path");
                ImageLoaderTask imageLoaderTask = new ImageLoaderTask();

                HashMap<String, Object> hmDownload = new HashMap<String, Object>();
                hm.put("flag_path",imgUrl);
                hm.put("position", i);

                // Starting ImageLoaderTask to download and populate image in the listview
                imageLoaderTask.execute(hm);
            }
        }
    }

    /** AsyncTask to download and load an image in ListView */
    private class ImageLoaderTask extends AsyncTask<HashMap<String, Object>, Void, HashMap<String, Object>>{

        @Override
        protected HashMap<String, Object> doInBackground(HashMap<String, Object>... hm) {

            InputStream iStream=null;
            String imgUrl = (String) hm[0].get("flag_path");
            int position = (Integer) hm[0].get("position");

            URL url;
            try {
                url = new URL(imgUrl);

                // Creating an http connection to communicate with url
                HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();

                // Connecting to url
                urlConnection.connect();

                // Reading data from url
                iStream = urlConnection.getInputStream();

                // Getting Caching directory
                File cacheDirectory = getBaseContext().getCacheDir();

                // Temporary file to store the downloaded image
                File tmpFile = new File(cacheDirectory.getPath() + "/wpta_"+position+".png");

                // The FileOutputStream to the temporary file
                FileOutputStream fOutStream = new FileOutputStream(tmpFile);

                // Creating a bitmap from the downloaded inputstream
                Bitmap b = BitmapFactory.decodeStream(iStream);

                // Writing the bitmap to the temporary file as png file
                b.compress(Bitmap.CompressFormat.PNG,100, fOutStream);

                // Flush the FileOutputStream
                fOutStream.flush();

                //Close the FileOutputStream
                fOutStream.close();

                // Create a hashmap object to store image path and its position in the listview
                HashMap<String, Object> hmBitmap = new HashMap<String, Object>();

                // Storing the path to the temporary image file
                hmBitmap.put("flag",tmpFile.getPath());

                // Storing the position of the image in the listview
                hmBitmap.put("position",position);

                // Returning the HashMap object containing the image path and position
                return hmBitmap;

            }catch (Exception e) {
                e.printStackTrace();
            }
            return null;
        }

        @Override
        protected void onPostExecute(HashMap<String, Object> result) {
            // Getting the path to the downloaded image
            String path = (String) result.get("flag");

            // Getting the position of the downloaded image
            int position = (Integer) result.get("position");

            // Getting adapter of the listview
            SimpleAdapter adapter = (SimpleAdapter ) mListView.getAdapter();

            // Getting the hashmap object at the specified position of the listview
            HashMap<String, Object> hm = (HashMap<String, Object>) adapter.getItem(position);

            // Overwriting the existing path in the adapter
            hm.put("flag",path);

            // Noticing listview about the dataset changes
            adapter.notifyDataSetChanged();
        }
    }
 }

Answer 1

在进行需要互联网访问的调用之前，您必须检查您的应用程序是否可以访问互联网。

以下方法检查您是否可以访问互联网。在您需要拨打互联网电话之前使用它。如果它 returns 为假，则向用户显示一条通知，说明需要互联网。

public boolean isInternetAvailable() {
    try {
        InetAddress ipAddr = InetAddress.getByName("google.com"); //You can replace it with your name

        if (ipAddr.equals("")) {
            return false;
        } else {
            return true;
        }

    } catch (Exception e) {
        return false;
    }

}

此外，如果您还没有添加这些权限：

<uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />

这样使用

if (isInternetAvailable() {
    // available network
} else {
    // no network
}

Answer 2

如果在 doInBackground() 期间抛出异常，您将返回 null，但随后您将在 onPostExecute() 中访问结果而不处理 null 情况。在尝试访问它之前，您需要验证结果不为空。像这样：

    @Override
    protected void onPostExecute(HashMap<String, Object> result) {
        if (result != null) {
            // Getting the path to the downloaded image
            String path = (String) result.get("flag");

Xml 正在解析 activity 如果没有连接则强制关闭

Xml Parsing activity force closes if no connection

android

xml-parsing