从/ proc / net / arp（Android）检索IP和MAC地址
好吧，根据本教程我有以下代码： http ： //android-er.blogspot.ro/2015/12/lookup-manufacturer-info-by-mac-address.html
但我做了一些改变！ 我不在MainActivity.java中运行它，我尝试在scanwifi.java中运行它
所以我在scanwifi.java中的代码是：
package com.nliplace.nli.unealta; import android.os.AsyncTask; import android.os.Bundle; import android.support.v7.app.AppCompatActivity; import android.view.View; import android.widget.AdapterView; import android.widget.ArrayAdapter; import android.widget.Button; import android.widget.ListView; import android.widget.TextView; import android.widget.Toast; import org.json.JSONArray; import org.json.JSONException; import org.json.JSONObject; import java.io.BufferedReader; import java.io.FileNotFoundException; import java.io.FileReader; import java.io.IOException; import java.io.InputStreamReader; import java.net.HttpURLConnection; import java.net.URL; import java.util.ArrayList; public class scanwifi extends AppCompatActivity { Button btnRead; TextView textResult; ListView listViewNode; ArrayList listNote; ArrayAdapter adapter; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); btnRead = (Button)findViewById(R.id.readclient); textResult = (TextView)findViewById(R.id.result); listViewNode = (ListView)findViewById(R.id.nodelist); listNote = new ArrayList(); ArrayAdapter adapter = new ArrayAdapter( scanwifi.this, android.R.layout.simple_list_item_1, listNote); listViewNode.setAdapter(adapter); listViewNode.setOnItemClickListener(new AdapterView.OnItemClickListener() { @Override public void onItemClick(AdapterView parent, View view, int position, long id) { Node node = (Node) parent.getAdapter().getItem(position); Toast.makeText(scanwifi.this, "MAC:\t" + node.mac + "\n" + "IP:\t" + node.ip + "\n" + "company:\t" + node.company + "\n" + "country:\t" + node.country + "\n" + "addressL1:\t" + node.addressL1 + "\n" + "addressL2:\t" + node.addressL2 + "\n" + "addressL3:\t" + node.addressL3 + "\n" + "type:\t" + node.type + "\n" + "startHex:\t" + node.startHex + "\n" + "endHex:\t" + node.endHex + "\n" + "startDec:\t" + node.startDec + "\n" + "endDec:\t" + node.endDec, Toast.LENGTH_SHORT).show(); } }); btnRead.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { new TaskReadAddresses(listNote, listViewNode).execute(); } }); } class Node { String ip; String mac; String jsonBody; String startHex; String endHex; String startDec; String endDec; String company; String addressL1; String addressL2; String addressL3; String country; String type; String remark; String queryString = "http://www.macvendorlookup.com/api/v2/"; Node(String ip, String mac){ this.ip = ip; this.mac = mac; queryMacVendorLookup(); } @Override public String toString() { return "IP: " + ip + "\n" + "MAC: " + mac + "\n" + company + "\n" + remark; } private String sendQuery(String qMac) throws IOException{ String result = ""; URL searchURL = new URL(queryString + qMac); HttpURLConnection httpURLConnection = (HttpURLConnection) searchURL.openConnection(); if(httpURLConnection.getResponseCode() == HttpURLConnection.HTTP_OK){ InputStreamReader inputStreamReader = new InputStreamReader(httpURLConnection.getInputStream()); BufferedReader bufferedReader = new BufferedReader( inputStreamReader, 8192); String line = null; while((line = bufferedReader.readLine()) != null){ result += line; } bufferedReader.close(); } return result; } private void ParseResult(String json){ try { JSONArray jsonArray = new JSONArray(json); JSONObject jsonObject = (JSONObject) jsonArray.get(0); startHex = jsonObject.getString("startHex"); endHex = jsonObject.getString("endHex"); startDec = jsonObject.getString("startDec"); endDec = jsonObject.getString("endDec"); company = jsonObject.getString("company"); addressL1 = jsonObject.getString("addressL1"); addressL2 = jsonObject.getString("addressL2"); addressL3 = jsonObject.getString("addressL3"); country = jsonObject.getString("country"); type = jsonObject.getString("type"); remark = "OK"; } catch (JSONException e) { e.printStackTrace(); remark = e.getMessage(); } } private void queryMacVendorLookup(){ try { jsonBody = sendQuery(mac); ParseResult(jsonBody); } catch (IOException e) { e.printStackTrace(); } } } private class TaskReadAddresses extends AsyncTask { ArrayList array; ListView listView; TaskReadAddresses(ArrayList array, ListView v){ listView = v; this.array = array; array.clear(); textResult.setText("querying..."); } @Override protected Void doInBackground(Void... params) { readAddresses(); return null; } @Override protected void onPostExecute(Void aVoid) { textResult.setText("Done"); } @Override protected void onProgressUpdate(Node... values) { listNote.add(values[0]); ((ArrayAdapter)(listView.getAdapter())).notifyDataSetChanged(); } private void readAddresses() { BufferedReader bufferedReader = null; try { bufferedReader = new BufferedReader(new FileReader("/proc/net/arp")); String line; while ((line = bufferedReader.readLine()) != null) { String[] splitted = line.split(" +"); if (splitted != null && splitted.length >= 4) { String ip = splitted[0]; String mac = splitted[3]; if (mac.matches("..:..:..:..:..:..")) { Node thisNode = new Node(ip, mac); publishProgress(thisNode); } } } } catch (FileNotFoundException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } finally{ try { bufferedReader.close(); } catch (IOException e) { e.printStackTrace(); } } } } }
我在activity_scanwifi.xml中的代码是：
当我用一个按钮调用scanwifi活动时，我得到了开发者consol这个错误：
FATAL EXCEPTION: main Process: com.nliplace.nli.unealta, PID: 29149 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.nliplace.nli.unealta/com.nliplace.nli.unealta.scanwifi}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2695) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2769) at android.app.ActivityThread.access$900(ActivityThread.java:177) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1430) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:135) at android.app.ActivityThread.main(ActivityThread.java:5910) 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:1405) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1200) Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference at com.nliplace.nli.unealta.scanwifi.onCreate(scanwifi.java:49) at android.app.Activity.performCreate(Activity.java:6178) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2648) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2769) at android.app.ActivityThread.access$900(ActivityThread.java:177) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1430) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:135) at android.app.ActivityThread.main(ActivityThread.java:5910) 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:1405) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1200)
所以任何想法为什么我得到这个，我该如何解决它？
我想的只是你设置setContentView(R.layout.activity_main); 那应该是setContentView(R.layout.activity_scanwifi); 。
这会导致NullPointerException因为findViewById没有在布局中找到视图。
我希望这可以帮助你。
您正在activity_scanwifi.xml中的列表视图上设置适配器
但是你设置了activity_main :: setContentView（R.layout.activity_main）;
将setContentView（R.layout.activity_main）更改为setContentView（R.layout.activity_scanwifi）