互联网连接关闭时 Android 应用程序崩溃

Question

我正在开发一个从互联网获取数据的安卓应用。当互联网连接保持打开时，应用程序可以正常工作。但是，当互联网连接保持关闭状态时，它就会崩溃。我在谷歌上搜索过，但找不到我的解决方案。我还在 Android Menifest 文件中添加了这些权限

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

我的全部代码如下，

public class NoticeBoard extends Activity {


ArrayList<String> title_array = new ArrayList<String>();
ArrayList<String> notice_array = new ArrayList<String>();

ListView list;
base_adapter3 adapter;
 TextView f;
TextView msg;



@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.list_notice);
    list = (ListView) findViewById(R.id.list_notice2);
    msg=(TextView)findViewById(R.id.error_msg);

    new test_ays().execute();

}




class test_ays extends AsyncTask<Void, Void, String> {

    @Override
    protected String doInBackground(Void... params) {
        String str = null ;
        try {
            HttpClient httpclient = new DefaultHttpClient();
            //HttpPost httppost = new HttpPost("http://10.0.2.2/BSDI/show.php");
            HttpPost httppost = new HttpPost("http://logger.net46.net/android_bsdi_tuhin/show.php");        
            HttpResponse response = httpclient.execute(httppost);
            str = EntityUtils.toString(response.getEntity());
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();



        }
        return str;


    }



@Override
protected void onPostExecute(String result) {

    super.onPostExecute(result);

     String response = result.toString();
     msg.setText(response);

   try {

        JSONArray new_array = new JSONArray(response);

        for (int i = 0, count = new_array.length(); i < count; i++) {
            try {
                JSONObject jsonObject = new_array.getJSONObject(i);
                title_array.add(jsonObject.getString("title").toString());
                notice_array.add(jsonObject.getString("notice").toString());

            } catch (JSONException e) {
                e.printStackTrace();

            }
        }

        adapter = new base_adapter3(NoticeBoard.this, title_array, notice_array);
      list.setAdapter(adapter);
       // f=(TextView) findViewById(R.id.textTuh);
       // f.setText(title_array);
    } catch (JSONException e) {
        // TODO Auto-generated catch block
       e.printStackTrace();

    }

}
}

}

我的 logcat 错误如下，

03-02 06:55:28.570: E/AndroidRuntime(788): FATAL EXCEPTION: main
03-02 06:55:28.570: E/AndroidRuntime(788): Process: com.example.bsdiassistant, PID: 788
03-02 06:55:28.570: E/AndroidRuntime(788): java.lang.NullPointerException
03-02 06:55:28.570: E/AndroidRuntime(788):  at     com.example.bsdiassistant.NoticeBoard$test_ays.onPostExecute(NoticeBoard.java:80)
03-02 06:55:28.570: E/AndroidRuntime(788):  at com.example.bsdiassistant.NoticeBoard$test_ays.onPostExecute(NoticeBoard.java:1)
03-02 06:55:28.570: E/AndroidRuntime(788):  at android.os.AsyncTask.finish(AsyncTask.java:632)
03-02 06:55:28.570: E/AndroidRuntime(788):  at android.os.AsyncTask.access$600(AsyncTask.java:177)
03-02 06:55:28.570: E/AndroidRuntime(788):  at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:645)
03-02 06:55:28.570: E/AndroidRuntime(788):  at android.os.Handler.dispatchMessage(Handler.java:102)
03-02 06:55:28.570: E/AndroidRuntime(788):  at android.os.Looper.loop(Looper.java:137)
03-02 06:55:28.570: E/AndroidRuntime(788):  at android.app.ActivityThread.main(ActivityThread.java:4998)
03-02 06:55:28.570: E/AndroidRuntime(788):  at java.lang.reflect.Method.invokeNative(Native Method)
03-02 06:55:28.570: E/AndroidRuntime(788):  at java.lang.reflect.Method.invoke(Method.java:515)
03-02 06:55:28.570: E/AndroidRuntime(788):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:777)
03-02 06:55:28.570: E/AndroidRuntime(788):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:593)
03-02 06:55:28.570: E/AndroidRuntime(788):  at dalvik.system.NativeStart.main(Native Method)

Answer 1

试试这段代码:

@Override
protected void onPostExecute(String result) {

    super.onPostExecute(result);

if(result!=null) // add this
 {  
     String response = result.toString();
     msg.setText(response);

   try {

        JSONArray new_array = new JSONArray(response);

        for (int i = 0, count = new_array.length(); i < count; i++) {
            try {
                JSONObject jsonObject = new_array.getJSONObject(i);
                title_array.add(jsonObject.getString("title").toString());
                notice_array.add(jsonObject.getString("notice").toString());

            } catch (JSONException e) {
                e.printStackTrace();

            }
        }

        adapter = new base_adapter3(NoticeBoard.this, title_array, notice_array);
      list.setAdapter(adapter);
       // f=(TextView) findViewById(R.id.textTuh);
       // f.setText(title_array);
    } catch (JSONException e) {
        // TODO Auto-generated catch block
       e.printStackTrace();

    }
}
}