没有显示-使用SimpleAdapter的ListView

Question

I'm trying to display a list of ALL the wifi AP's in range ie including those with same SSID's as these are not shown in the default wifi settings.

This is my first attempt at Android SDK and I've gotten so far:

package com.iiitd.wifistats;

import android.app.Activity;
import android.content.Context;
import android.net.wifi.ScanResult;
import android.net.wifi.WifiManager;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
import android.widget.ListView;
import android.widget.SimpleAdapter;
import android.widget.Toast;

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

public class WiFiStats extends Activity implements View.OnClickListener {

    WifiManager wifi;
    List<ScanResult> scanResults;
    ArrayList<Map<String, Integer>> list;
    SimpleAdapter adapter;
    ListView listview;

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

        wifi = (WifiManager) getSystemService(Context.WIFI_SERVICE);
        if (!wifi.isWifiEnabled()) {
            Toast.makeText(getApplicationContext(), "Turning on WiFi...", Toast.LENGTH_LONG).show();
            wifi.setWifiEnabled(true);
        }

        carryON();
    }

    private void carryON(){
        final Button button = (Button) findViewById(R.id.buttonScan);
        button.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                wifi = (WifiManager) v.getContext().getSystemService(Context.WIFI_SERVICE);
                scanResults = wifi.getScanResults();
                Toast.makeText(getApplicationContext(), "Scanning...", Toast.LENGTH_SHORT).show();
                list = buildData(scanResults);
                //Toast.makeText(getApplicationContext(), list.toString(), Toast.LENGTH_SHORT).show();
                adapter = new SimpleAdapter(v.getContext(), list, R.layout.listitem, new String[]{"BSSID", "strength"}, new int[] {R.id.BSSID, R.id.strength});
                //Toast.makeText(getApplicationContext(), adapter.toString(), Toast.LENGTH_SHORT).show();
                listview = (ListView) findViewById(R.id.list);
                listview.setAdapter(adapter);
            }
        });
    }

    private ArrayList<Map<String, Integer>> buildData(java.util.List<ScanResult> s) {
        ArrayList<Map<String, Integer>> list = new ArrayList<Map<String, Integer>>();
        for (ScanResult result : s) {
            list.add(putData(result.BSSID, result.level));
        }
        return list;
    }

    private HashMap<String, Integer> putData(String BSSID, int level) {
        HashMap<String, Integer> item = new HashMap<String, Integer>();
        item.put(BSSID, level);
        return item;
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.wi_fi_stats, menu);
        return true;
    }

    @Override
    public void onClick(View view) {

    }
}

This is my activity_xml:

    <RelativeLayout
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        xmlns:android="http://schemas.android.com/apk/res/android">

    <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Scan"
            android:id="@+id/buttonScan"
            android:layout_alignParentBottom="true"
            android:layout_centerHorizontal="true"/>

    <ListView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/list"
            android:layout_above="@+id/buttonScan"
            android:layout_alignParentLeft="true"
            android:layout_marginBottom="14dp"/>
</RelativeLayout>

And this is listitem.xml:

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
                android:layout_width="fill_parent"
                android:layout_height="?android:attr/listPreferredItemHeight"
                android:padding="6dip">

    <TextView
            android:id="@+id/strength"
            android:layout_width="fill_parent"
            android:layout_height="26dip"
            android:layout_alignParentBottom="true"
            android:layout_alignParentRight="true"
            android:ellipsize="marquee"
            android:singleLine="true"
            android:text="Description"
            android:textSize="12sp"/>
    <TextView
            android:id="@+id/BSSID"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_above="@id/strength"
            android:layout_alignParentRight="true"
            android:layout_alignParentTop="true"
            android:layout_alignWithParentIfMissing="true"
            android:gravity="center_vertical"
            android:text="Example application"
            android:textSize="16sp"/>

</RelativeLayout>

There is no list displayed when the I start a scan. However, if I use a toast, the I can see that the list is forming correctly. Can someone guide me here? Thanks.

Answer 1

Take a look at the code here

adapter = new SimpleAdapter(v.getContext(), list, R.layout.listitem, new String[]{"BSSID", "strength"}, new int[] {R.id.BSSID, R.id.strength});

The String array is telling the adapter the keys to be used when accessing the map that you define. In your code, you are assigning the values as such

private HashMap<String, Integer> putData(String BSSID, int level) {
    HashMap<String, Integer> item = new HashMap<String, Integer>();
    item.put(BSSID, level);
    return item;
}

This is assigning the int for level to the key set by the String BSSID. You need to change all occurrences of HashMap in your code to take a String value and a String key HashMap< String, String > and replace the method with the following

private HashMap<String, String> putData(String BSSID, int level) {
    HashMap<String, String> item = new HashMap<String, String>();
    item.put("BSSID", BSSID);
    item.put("strength", Integer.toString(level));
    return item;
}

Answer 2

have you tried extending ListActivity instead of a plain activity? you could need to change the ID of the ListView in your XML to android:id="@id/android:list"

Then in your caryON() method you would call setListAdapter(adapter); after initialising the new Simple Adapter

adapter = new SimpleAdapter(v.getContext(), list, R.layout.listitem, new String[]{"BSSID", "strength"}, new int[] {R.id.BSSID, R.id.strength});
setListAdapter(adapter);