Question

我使用AsyncTask来验证服务器可用性。

class RetrieveFeedTask extends AsyncTask<String, String, Map<String, String>> {

    private Exception exception;
    ArrayList<String> str = new ArrayList<String>();
    Map<String, String> statusMap = new HashMap<>();

    private String job;
    public ReturnData returnData;
    public HomeFragment homeFragment = new HomeFragment();
    public AsyncResponse delegate;
    Socket socket = null;

    public void params(String job){
        this.job = job;
    }

    public void setAsyncResponse(AsyncResponse deletate){
        this.delegate = deletate;
    }


    @Override
    protected Map<String, String> doInBackground(String... params){

        //ports: 8080 5060,5070,5080
        if(job.equals("checkConn")) {

            statusMap.clear();

            boolean reachable = true;
            boolean wwwServ = true;
            try {
                InetAddress address = InetAddress.getByName(params[0]);
                reachable = address.isReachable(10000);
                Log.d("lab", "IP: "+ reachable);
            } catch (Exception e){
            }
            try {
                (new Socket(params[0], 8080)).close();
            }
            catch (UnknownHostException e)
            {
                wwwServ = false;
            }
            catch (IOException e)
            {
                wwwServ = false;
            }
            Log.d("lab", "WWW: " + wwwServ);
            Log.d("lab", "Rozmiar listy: " + Integer.toString(str.size()));
            //add values to map
            statusMap.put("IP", Boolean.toString(reachable));
            statusMap.put("WWW", Boolean.toString(wwwServ));
        }
         return statusMap;
    }
    @Override
    protected void onPostExecute(Map<String, String> result) {
        // Result is here now, may be 6 different List type.
        Log.d("lab", "The returned list contains " +result.size()+ "elements");
        delegate.processFinish(result);
    }

}

AsyncTask返回地图。一切都很好，直到我作为onCreateView的功能运行它。移动到onClick函数时出现问题。我这样做是因为，只有当用户点击了卡而不是按钮时，状态才会更新。

public class HomeFragment extends Fragment implements AsyncResponse{

    Button checkConn;
    TextView statusIP,statusWWW;
    SharedPreferences savedSettings;
    SharedPreferences.Editor editor;
    private ArrayList<String> lista = new ArrayList<String>();
    private Map<String, String> statusMap = new HashMap<>();

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
            Bundle savedInstanceState) {


        final RetrieveFeedTask task = new RetrieveFeedTask();
        task.setAsyncResponse(this);
        task.params("checkConn");

        savedSettings = getActivity().getSharedPreferences("lab.linuxservice.com.linuxservice", Context.MODE_PRIVATE); //load shared preferences
        editor = savedSettings.edit();

        View rootView = inflater.inflate(R.layout.fragment_home, container, false);

        statusIP = (TextView)rootView.findViewById(R.id.ipStatusText);
        statusWWW = (TextView)rootView.findViewById(R.id.sipServerStatusText);

        checkConn = (Button) rootView.findViewById(R.id.checkConn);
        checkConn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v)   {

                Log.d("lab", "Rozmiar listy w onCreateView: " + Integer.toString(statusMap.size()));

                String data[] = {savedSettings.getString("IP", "")};
                task.execute(data); //chceck connection on click

                String ipStatus = statusMap.get("IP");
                String wwwStatus = statusMap.get("WWW");

                Log.d("lab", "ipStatus: " + ipStatus);

                if(ipStatus.equals("false")){
                    statusIP.setText("Unavailable");
                 }
                else{
                    statusIP.setText("Available");
                }

                if(wwwStatus.equals("false")){
                    statusWWW.setText("Unavailable");
                }
                else{
                    statusWWW.setText("Available");
                }

                Toast.makeText(getActivity(), "Checking: ", Toast.LENGTH_SHORT).show();


            }
        });

        return rootView;
    }

    public void processFinish(Map<String, String> output) {
        this.statusMap = output;
    }
}

如何在onClick中启动AsyncTask-得到此错误：

 java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.equals(java.lang.Object)' on a null object reference
            at lab.linuxservice.com.linuxservice.HomeFragment$1.onClick(HomeFragment.java:132)

该行表示：

if(ipStatus.equals("false"))

当我等待9秒Thread.sleep(9000); Log.d("lab", "ipStatus wolam: " + ipStatus); ipStatus为空时，当我第二次单击按钮ipStatus不为空时，为真。

更新

我这样做：

  public  TextView statusIP,statusWWW;

 @Override
    protected void onPostExecute(Map<String, String> result) {
        // Result is here now, may be 6 different List type.
        Log.d("lab", "The returned list contains " + result.size() + "elements");
        delegate.processFinish(result);
        homeFragment.updateView(view,result);

        String ipStatus = statusMap.get("IP");
        String wwwStatus = statusMap.get("WWW");

        Log.d("lab", "ipStatus wolam: " + ipStatus);

        statusIP = (TextView)view.findViewById(R.id.ipStatusText);


        if(ipStatus.equals("false")){
            statusIP.setText("Unavailable");
        }
        else{
            statusIP.setText("Available");
        }
        if(wwwStatus.equals("false")){
            statusWWW.setText("Unavailable");
        }
        else{
            statusWWW.setText("Available");
        }
        Log.d("lab","wykonuje onPostExecute");


    }

在RetrieveFeedTask但是，收到错误：

   java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference

Answer 1

您收到此错误，因为ipStatus变量为null。 AsyncTask完成后设置此变量的值，并为您提供状态图。这意味着将行String ipStatus = statusMap.get("IP");移动到AsyncTask的onPostExecute()方法。

Android，点击按钮检查服务器连接

1 个答案: