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How does make Identify Task in ArcGIS API for android work with a standard WMS

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I want to use Identify Task in ARCGIS API for android.I used this example and it works fine but when I try to change the URL to get data from another WMS it shows error here is my another wms I get error in folowing line

for (int index = 0; index < results.length; index++) {

result_1 = results[index];
String displayFieldName = result_1.getDisplayFieldName();
Map<String, Object> attr = result_1.getAttributes();
for (String key : attr.keySet()) {
if (key.equalsIgnoreCase(displayFieldName)) {
resultList.add(result_1);
}
}
}

in this class which I have got from example

 package com.esri.arcgis.android.samples.identifytask;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;

import android.app.Activity;
import android.app.ProgressDialog;
import android.content.Context;
import android.content.res.Resources;
import android.graphics.Color;
import android.os.AsyncTask;
import android.os.Bundle;
import android.view.Gravity;
import android.view.View;
import android.view.ViewGroup;
import android.view.ViewGroup.LayoutParams;
import android.widget.LinearLayout;
import android.widget.ListView;
import android.widget.TextView;

import com.esri.android.action.IdentifyResultSpinner;
import com.esri.android.action.IdentifyResultSpinnerAdapter;
import com.esri.android.map.Callout;
import com.esri.android.map.MapView;
import com.esri.android.map.ags.ArcGISTiledMapServiceLayer;
import com.esri.android.map.event.OnSingleTapListener;
import com.esri.core.geometry.Envelope;
import com.esri.core.geometry.Point;
import com.esri.core.tasks.identify.IdentifyParameters;
import com.esri.core.tasks.identify.IdentifyResult;
import com.esri.core.tasks.identify.IdentifyTask;

/**
 * This sample allows the user to identify data based on single tap and view the
 * results in a callout window which has a spinner in its layout. Also the user
 * can select any of the results displayed and view its details. The details are
 * the attribute values.
 * 
 * The output value shown in the spinner is the display field.
 * 
 */

public class Identify extends Activity {

// create ArcGIS objects
MapView mMapView = null;
IdentifyParameters params = null;

// create UI objects
static ProgressDialog dialog;

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    // Retrieve the map and initial extent from XML layout
    mMapView = (MapView) findViewById(R.id.map);

    // add demographic layer to the map
    mMapView.addLayer(new ArcGISTiledMapServiceLayer(this.getResources()
            .getString(R.string.identify_task_url_for_avghouseholdsize)));

    // set Identify Parameters
    params = new IdentifyParameters();
    params.setTolerance(20);
    params.setDPI(98);
    params.setLayers(new int[] { 4 });
    params.setLayerMode(IdentifyParameters.ALL_LAYERS);

    // Identify on single tap of map
    mMapView.setOnSingleTapListener(new OnSingleTapListener() {

        private static final long serialVersionUID = 1L;

        @Override
        public void onSingleTap(final float x, final float y) {

            if (!mMapView.isLoaded()) {
                return;
            }

            // Add to Identify Parameters based on tapped location
            Point identifyPoint = mMapView.toMapPoint(x, y);

            params.setGeometry(identifyPoint);
            params.setSpatialReference(mMapView.getSpatialReference());
            params.setMapHeight(mMapView.getHeight());
            params.setMapWidth(mMapView.getWidth());
            params.setReturnGeometry(false);

            // add the area of extent to identify parameters
            Envelope env = new Envelope();
            mMapView.getExtent().queryEnvelope(env);
            params.setMapExtent(env);

            // execute the identify task off UI thread
            MyIdentifyTask mTask = new MyIdentifyTask(identifyPoint);
            mTask.execute(params);
        }

    });

}

private ViewGroup createIdentifyContent(final List<IdentifyResult> results) {

    // create a new LinearLayout in application context
    LinearLayout layout = new LinearLayout(this);

    // view height and widthwrap content
    layout.setLayoutParams(new LayoutParams(LayoutParams.WRAP_CONTENT,
            LayoutParams.WRAP_CONTENT));

    // default orientation
    layout.setOrientation(LinearLayout.HORIZONTAL);

    // Spinner to hold the results of an identify operation
    IdentifyResultSpinner spinner = new IdentifyResultSpinner(this, results);

    // make view clickable
    spinner.setClickable(false);
    spinner.canScrollHorizontally(BIND_ADJUST_WITH_ACTIVITY);

    // MyIdentifyAdapter creates a bridge between spinner and it's data
    MyIdentifyAdapter adapter = new MyIdentifyAdapter(this, results);
    spinner.setAdapter(adapter);
    spinner.setLayoutParams(new LayoutParams(LayoutParams.MATCH_PARENT,
            LayoutParams.WRAP_CONTENT));
    layout.addView(spinner);

    return layout;
}

/**
 * This class allows the user to customize the string shown in the callout.
 * By default its the display field name.
 * 
 * A spinner adapter defines two different views; one that shows the data in
 * the spinner itself and one that shows the data in the drop down list when
 * spinner is pressed.
 * 
 */
public class MyIdentifyAdapter extends IdentifyResultSpinnerAdapter {
    String m_show = null;
    List<IdentifyResult> resultList;
    int currentDataViewed = -1;
    Context m_context;

    public MyIdentifyAdapter(Context context, List<IdentifyResult> results) {
        super(context, results);
        this.resultList = results;
        this.m_context = context;
    }

    // Get a TextView that displays identify results in the callout.
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        String LSP = System.getProperty("line.separator");
        StringBuilder outputVal = new StringBuilder();

        // Resource Object to access the Resource fields
        Resources res = getResources();

        // Get Name attribute from identify results
        IdentifyResult curResult = this.resultList.get(position);

        if (curResult.getAttributes().containsKey(
                res.getString(R.string.NAME))) {
            outputVal.append("Place: "
                    + curResult.getAttributes()
                            .get(res.getString(R.string.NAME)).toString());
            outputVal.append(LSP);
        }

        if (curResult.getAttributes().containsKey(
                res.getString(R.string.ID))) {
            outputVal.append("State ID: "
                    + curResult.getAttributes()
                            .get(res.getString(R.string.ID)).toString());
            outputVal.append(LSP);
        }

        if (curResult.getAttributes().containsKey(
                res.getString(R.string.ST_ABBREV))) {
            outputVal.append("Abbreviation: "
                    + curResult.getAttributes()
                            .get(res.getString(R.string.ST_ABBREV))
                            .toString());
            outputVal.append(LSP);
        }

        if (curResult.getAttributes().containsKey(
                res.getString(R.string.TOTPOP_CY))) {
            outputVal.append("Population: "
                    + curResult.getAttributes()
                            .get(res.getString(R.string.TOTPOP_CY))
                            .toString());
            outputVal.append(LSP);

        }

        if (curResult.getAttributes().containsKey(
                res.getString(R.string.LANDAREA))) {
            outputVal.append("Area: "
                    + curResult.getAttributes()
                            .get(res.getString(R.string.LANDAREA))
                            .toString());
            outputVal.append(LSP);

        }

        // Create a TextView to write identify results
        TextView txtView;
        txtView = new TextView(this.m_context);
        txtView.setText(outputVal);
        txtView.setTextColor(Color.BLACK);
        txtView.setLayoutParams(new ListView.LayoutParams(
                LayoutParams.MATCH_PARENT, LayoutParams.WRAP_CONTENT));
        txtView.setGravity(Gravity.CENTER_VERTICAL);

        return txtView;
    }
}

@Override
protected void onPause() {
    super.onPause();
    mMapView.pause();
}

@Override
protected void onResume() {
    super.onResume();
    mMapView.unpause();
}

private class MyIdentifyTask extends
        AsyncTask<IdentifyParameters, Void, IdentifyResult[]> {

    IdentifyTask task = new IdentifyTask(Identify.this.getResources()
            .getString(R.string.identify_task_url_for_avghouseholdsize));

    IdentifyResult[] M_Result;

    Point mAnchor;

    MyIdentifyTask(Point anchorPoint) {
        mAnchor = anchorPoint;
    }

    @Override
    protected void onPreExecute() {
        // create dialog while working off UI thread
        dialog = ProgressDialog.show(Identify.this, "Identify Task",
                "Identify query ...");

    }

    protected IdentifyResult[] doInBackground(IdentifyParameters... params) {

        // check that you have the identify parameters
        if (params != null && params.length > 0) {
            IdentifyParameters mParams = params[0];

            try {
                // Run IdentifyTask with Identify Parameters

                M_Result = task.execute(mParams);

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

        return M_Result;
    }

    @Override
    protected void onPostExecute(IdentifyResult[] results) {

        // dismiss dialog
        if (dialog.isShowing()) {
            dialog.dismiss();
        }

        ArrayList<IdentifyResult> resultList = new ArrayList<IdentifyResult>();

        IdentifyResult result_1;

        for (int index = 0; index < results.length; index++) {

            result_1 = results[index];
            String displayFieldName = result_1.getDisplayFieldName();
            Map<String, Object> attr = result_1.getAttributes();
            for (String key : attr.keySet()) {
                if (key.equalsIgnoreCase(displayFieldName)) {
                    resultList.add(result_1);
                }
            }
        }

        Callout callout = mMapView.getCallout();
        callout.setContent(createIdentifyContent(resultList));
        callout.show(mAnchor);


    }
}
}

and this is error

06-11 19:01:21.384 18989-18989/com.tehranuni.hazard.hazard E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.tehranuni.hazard.hazard, PID: 18989
java.lang.NullPointerException: Attempt to get length of null array
at com.tehranuni.hazard.hazard.gatter_geo_data$MyIdentifyTask.onPostExecute(gatter_geo_data.java:714)
at com.tehranuni.hazard.hazard.gatter_geo_data$MyIdentifyTask.onPostExecute(gatter_geo_data.java:661)
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:211)
at android.app.ActivityThread.main(ActivityThread.java:5321)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1016)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:811)
at de.robv.android.xposed.XposedBridge.main(XposedBridge.java:117)

As the error say results is null and I think it is because it does not get fields from WMS layer.What so you think about this error?Is there any way to fix it?

Thank you so much for your help

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