Question

I want to display an error message when the MYSQL database can not be access due to sudden network disconnection how can i do this. Currently my application crash when this happens

I am using the below class to display the values to a Listview

import android.app.Activity;
import android.app.AlertDialog;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.database.Cursor;
import android.os.AsyncTask;
import android.os.Bundle;
import android.os.Handler;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.CursorAdapter;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;

import org.json.JSONArray;


public class ViewActivity extends Activity  {



    ListView Listview;

    String url_get_All ="http://102.128.2.5/ABC/DisplayAll.php";

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


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



        new GetAll().execute(new APConnect());

        View empty = findViewById(R.id.empty);
        Listview.setEmptyView(empty);

    }



    public void setlistArray(JSONArray jsonArray)
    {
        this.Listview.setAdapter(new ListAdapter(jsonArray,this));
    }

    class GetAll extends AsyncTask<APConnect, Long, JSONArray>
    {

        @Override
        protected JSONArray doInBackground(APConnect... params) {
            return  params[0].Getconnect(url_get_All);
        }


        @Override
        protected void onPostExecute(JSONArray jsonArray) {
            super.onPostExecute(jsonArray);
            setlistArray(jsonArray);
        }
    }

}

I have used the below Adapter class

public class ListAdapter extends BaseAdapter {

    private JSONArray listArray;
    private LayoutInflater inflater = null;
    Activity cust;

    public ListAdapter(JSONArray jsonarray,   Activity cust)
    {
        listArray = jsonarray;
        this.cust = cust;
        inflater = (LayoutInflater) this.cust.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    }


    @Override
    public int getCount() {
        return this.listArray.length();
    }

    @Override
    public Object getItem(int position) {
        return position;
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {

        ItemsinListCall call;
        // The view need to be setup
        if(convertView == null)
        {

            convertView = inflater.inflate(R.layout.custodianrow_views,null);
            call = new ItemsinListCall();
            call.ID = (TextView) convertView.findViewById(R.id.id_view);
            call.Name = (TextView) convertView.findViewById(R.id.name_view);
            call.Desin = (TextView) convertView.findViewById(R.id.Desig_view);
            call.Depar= (TextView) convertView.findViewById(R.id.Depar_view);

            convertView.setTag(call);
        }
        else
        {
            call = (ItemsinListCall) convertView.getTag();
        }


        try {
            JSONObject jsonObject = this.listArray.getJSONObject(position);
            call.ID.setText(jsonObject.getString("id"));
            call.Name.setText(jsonObject.getString("name"));
            call.Desin.setText(jsonObject.getString("Desin"));
            call.Depar.setText(jsonObject.getString("Depar"));

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

        return convertView;

    }

    private class ItemsinListCall
    {
        private TextView ID;
        private TextView Name;
        private TextView Desin;
        private TextView Depar;
    }
}

And i have used the APconnect to connect to the webserver to access the PHP code

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.util.EntityUtils;
import org.json.JSONArray;
import org.json.JSONException;
import java.io.IOException;
import java.util.List;


public class APConnect {

     public JSONArray Getconnect(String url)
        {

            HttpEntity httpEntity = null;

            try
            {

                DefaultHttpClient httpClient = new DefaultHttpClient();

                HttpGet httpGet = new HttpGet(url);

                HttpResponse httpResponse = httpClient.execute(httpGet);

                httpEntity = httpResponse.getEntity();


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


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



            JSONArray jsonArray = null;



                try {
                    String entityResponse = EntityUtils.toString(httpEntity);
                    Log.e("Entity Responce",entityResponse);

                    jsonArray = new JSONArray(entityResponse);

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



            return jsonArray;
        }
    }

I am getting the below error message

java.lang.NullPointerException
        at com.example.nms.ListAdapter.getCount(ListAdapter.java:35)
        at android.widget.setlistArray.setAdapter(ListView.java:486)
        at com.example.nams.ViewActivity.setlistArray(ViewActivity.java:80)
        at com.example.nams.ViewActivity$GetAll.onPostExecute(ViewActivity.java:140)
        at com.example.nams.ViewActivity$GetAll.onPostExecute(ViewActivity.java:110)
        at android.os.AsyncTask.finish(AsyncTask.java:632)
        at android.os.AsyncTask.access$600(AsyncTask.java:177)
        at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:645)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:157)
        at android.app.ActivityThread.main(ActivityThread.java:5356)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:515)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1265)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1081)
        at dalvik.system.NativeStart.main(Native Method)

Answer 1

Change this

return this.listArray.length();

To

return listArray==null?0:listArray.length();

And change

public void setlistArray(JSONArray jsonArray)
{
    this.Listview.setAdapter(new ListAdapter(jsonArray,this));
}

to

public void setlistArray(JSONArray jsonArray)
{ 
   if(jsonArray == null){
            //Show toast error
    }else
    this.Listview.setAdapter(new ListAdapter(jsonArray,this));
}

This is just my suggestion, you can make it better. You should split your task to many difference classes and one class will handle one task

Displaying an Error Message When Android App cannot connect to MYSQL

1 个答案: