Question

我是java和android编程的新手，但我接受了朋友推出的挑战，现在我必须努力工作。

我终于设法让这种类型的活动与AsyncTask一起工作，但它似乎在所有android上都运行良好，但在4.4.2 KitKat上却没有。

问题似乎是在url.openConnection上，我多次尝试改变我的方式，但我没有取得积极成果...... 我只需要从URL读取文件这是我的班级代码：

public class MenuActivity extends Activity {

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

        new HttpTask().execute();
    }

    public final class HttpTask
            extends
            AsyncTask<String/* Param */, Boolean /* Progress */, String /* Result */> {

        private HttpClient mHc = new DefaultHttpClient();

        @Override
        protected String doInBackground(String... params) {
            publishProgress(true);
            InputStream inputstream = null;

            URL url = null;
            try {
                url = new URL("http://somesite/prova.txt");
            } catch (MalformedURLException e) {
                e.printStackTrace();
            }

            assert url != null;
            URLConnection connection = null;
            try {
                connection = url.openConnection();
            } catch (IOException e) {
                e.printStackTrace();
            }

            try {
                HttpURLConnection httpConnection = (HttpURLConnection) connection;
                httpConnection.setRequestMethod("GET");
                httpConnection.connect();

                if (httpConnection.getResponseCode() == HttpURLConnection.HTTP_OK) {
                    inputstream = httpConnection.getInputStream();
                }
            } catch (Exception ex) {
                ex.printStackTrace();
            }

            ByteArrayOutputStream bytearryoutputstream = new ByteArrayOutputStream();
            int i;
            try {
                i = inputstream.read();
                while (i != -1) {
                    bytearryoutputstream.write(i);
                    i = inputstream.read();
                }
                inputstream.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return bytearryoutputstream.toString();
        }

        @Override
        protected void onProgressUpdate(Boolean... progress) {

        }

        @Override
        protected void onPostExecute(String result) {

            StringBuilder nuovafrase=new StringBuilder("");

            String[] frasone=result.split("\n");

            ListView listView = (ListView)findViewById(R.id.listViewDemo);

            ArrayAdapter<String> arrayAdapter;
            arrayAdapter = new ArrayAdapter<String>(getApplicationContext(), R.layout.rowmenu, R.id.textViewList, frasone);
            listView.setAdapter(arrayAdapter);

        }


    }
}

这就是Logcat ......

03-11 17:49:37.955    1277-1294/com.example.appsb.app W/System.err﹕                 atjava.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
      03-11 17:49:37.955    1277-1294/com.example.appsb.app W/System.err﹕ at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
       03-11 17:49:37.959    1277-1294/com.example.appsb.app W/System.err﹕ at java.lang.Thread.run(Thread.java:841)
       03-11 17:49:37.959    1277-1294/com.example.appsb.app W/System.err﹕ Caused by: libcore.io.GaiException: getaddrinfo failed: EAI_NODATA (No address associated with hostname)
         03-11 17:49:37.959    1277-1294/com.example.appsb.app W/System.err﹕ at libcore.io.Posix.getaddrinfo(Native Method)
       03-11 17:49:37.959    1277-1294/com.example.appsb.app W/System.err﹕ at libcore.io.ForwardingOs.getaddrinfo(ForwardingOs.java:61)
         03-11 17:49:37.959    1277-1294/com.example.appsb.app W/System.err﹕ at java.net.InetAddress.lookupHostByName(InetAddress.java:405)
      03-11 17:49:37.959    1277-1294/com.example.appsb.app W/System.err﹕ ... 18 more
        03-11 17:49:37.959    1277-1294/com.example.appsb.app W/System.err﹕ Caused by: libcore.io.ErrnoException: getaddrinfo failed: EACCES (Permission denied)
        03-11 17:49:37.959    1277-1294/com.example.appsb.app W/System.err﹕ ... 21 more
         03-11 17:49:37.963    1277-1294/com.example.appsb.app W/dalvikvm﹕ threadid=11: thread exiting with uncaught exception (group=0xa4d69b20)
             03-11 17:49:37.963    1277-1294/com.example.appsb.app E/AndroidRuntime﹕               FATAL EXCEPTION: AsyncTask #1
         Process: com.example.appsb.app, PID: 1277
             java.lang.RuntimeException: An error occured while executing doInBackground()
        at android.os.AsyncTask$3.done(AsyncTask.java:300)
        at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355)
        at java.util.concurrent.FutureTask.setException(FutureTask.java:222)
        at java.util.concurrent.FutureTask.run(FutureTask.java:242)
        at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
        at               java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
              at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
                   at java.lang.Thread.run(Thread.java:841)
             Caused by: java.lang.NullPointerException
                   at          com.example.appsb.app.MenuActivity$HttpTask.doInBackground(MenuActivity.java:74)
                    at com.example.appsb.app.MenuActivity$HttpTask.doInBackground(MenuActivity.java:33)
                   at android.os.AsyncTask$2.call(AsyncTask.java:288)
                    at java.util.concurrent.FutureTask.run(FutureTask.java:237)
                            at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
                       at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
                         at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
                      at java.lang.Thread.run(Thread.java:841)

有一个引起：java.lang.NullPointerException，但我不明白为什么......

谢谢

Answer 1

可能是inputstream为null造成的。只有在响应代码为inputstream时才会初始化OK。因此，您需要检查返回的响应代码。如果它没有导致错误，我仍然会添加一些代码，如果响应代码不是OK。如果无法连接，您不希望应用程序崩溃。您至少应该显示一条有用的错误消息例如：

else{
    showErrorMsg();
    return null;
}

Answer 2

尝试inputstream.read（）;

时捕获FileNotFoundException

try {
    i = inputstream.read();
    while (i != -1) {
        bytearryoutputstream.write(i);
        i = inputstream.read();
    }
    inputstream.close();
} catch (FileNotFoundException e) {
    Log.e("MyTag","Handling empty page...");
} catch (IOException e) {
    Log.e("MyTag",e.toString());
}

来自URL的KitKat连接在AsyncTask中获取NullPointerException

2 个答案: