無法獲取在ip地址mac地址上運行的代碼

-1

我正在使用網絡掃描程序，並且遇到此代碼。
但我無法找到問題所在。
我收到異常，如果有人可以幫助調試這個，它將不勝感激。無法獲取在ip地址mac地址上運行的代碼

MainActivity

package com.example.george.droidscanner; 

import android.os.AsyncTask; 
import android.os.Bundle; 
import android.support.v7.app.AppCompatActivity; 
import android.view.View; 
import android.widget.ArrayAdapter; 
import android.widget.Button; 
import android.widget.ListView; 
import android.widget.TextView; 

import java.io.BufferedReader; 
import java.io.FileNotFoundException; 
import java.io.FileReader; 
import java.io.IOException; 
import java.net.InetAddress; 
import java.net.UnknownHostException; 
import java.util.ArrayList; 

public class MainActivity extends AppCompatActivity { 

    Button btnRead; 
    TextView textResult; 

    ListView listViewNode; 
    ArrayList<Node> listNote; 
    ArrayAdapter<Node> 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<Node> adapter = 
       new ArrayAdapter<Node>(
         MainActivity.this, 
         android.R.layout.simple_list_item_1, 
         listNote); 
     listViewNode.setAdapter(adapter); 

     btnRead.setOnClickListener(new View.OnClickListener() { 
      @Override 
      public void onClick(View v) { 
       new TaskReadAddresses(listNote, listViewNode).execute(); 
      } 
     }); 
    } 

    class Node { 
     String ip; 
     String mac; 
     String CanonicalHostName; 
     String HostName; 
     String LocalHostCanonicalHostName; 
     String LocalHostHostName; 
     String remark; 
     boolean isReachable; 

     Node(String ip, String mac){ 
      this.ip = ip; 
      this.mac = mac; 
      queryHost(); 
     } 

     @Override 
     public String toString() { 
      return "IP: " + ip + "\n" + 
        "MAC: " + mac + "\n" + 
        "CanonicalHostName:\t" + CanonicalHostName + "\n" + 
        "HostName:\t" + HostName + "\n" + 
        "getLocalHost().getCanonicalHostName():\t" + LocalHostCanonicalHostName + "\n" + 
        "getLocalHost().getHostName():\t" + LocalHostHostName + "\n" + 
        "isReachable: " + isReachable + 
        "\n" + remark; 
     } 

     private void queryHost(){ 
      try { 
       InetAddress inetAddress = InetAddress.getByName(ip); 
       CanonicalHostName = inetAddress.getCanonicalHostName(); 
       HostName = inetAddress.getHostName(); 
       LocalHostCanonicalHostName = inetAddress.getLocalHost().getCanonicalHostName(); 
       LocalHostHostName = inetAddress.getLocalHost().getHostName(); 
       isReachable = inetAddress.isReachable(3000); 

      } catch (UnknownHostException e) { 
       e.printStackTrace(); 
       remark = e.getMessage(); 
      } catch (IOException e) { 
       e.printStackTrace(); 
       remark = e.getMessage(); 
      } 
     } 
    } 

    private class TaskReadAddresses extends AsyncTask<Void, Node, Void> { 

     ArrayList<Node> array; 
     ListView listView; 

     TaskReadAddresses(ArrayList<Node> 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(); 
       } 
      } 
     } 
    } 
}

佈局文件。

Activity_main.xml 
<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    xmlns:tools="http://schemas.android.com/tools" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    android:padding="16dp" 
    android:orientation="vertical" 
    tools:context="com.example.george.droidscanner.MainActivity"> 

    <TextView 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:layout_gravity="center_horizontal" 
     android:autoLink="web" 
     android:text="http://android-er.blogspot.com/" 
     android:textStyle="bold" /> 

    <Button 
     android:id="@+id/readclient" 
     android:layout_width="match_parent" 
     android:layout_height="wrap_content" 
     android:textAllCaps="false" 
     android:text="Read Ip/MAC addresses"/> 

    <TextView 
     android:id="@+id/result" 
     android:layout_width="match_parent" 
     android:layout_height="wrap_content" 
     android:typeface="monospace" 
     android:textSize="24sp"/> 
</LinearLayout>

自定義適配器nodelist.xml

<?xml version="1.0" encoding="utf-8"?> 
<ListView xmlns:android="http://schemas.android.com/apk/res/android" 
    android:orientation="vertical" 
    android:layout_width="match_parent" 
    android:id="@+id/nodelist" 
    android:layout_height="match_parent"> 

</ListView>

運行時錯誤

E/AndroidRuntime: FATAL EXCEPTION: main 
        Process: com.example.george.droidscanner, PID: 2481 
        java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.george.droidscanner/com.example.george.droidscanner.MainActivity}: 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:2325) 
         at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387) 
         at android.app.ActivityThread.access$800(ActivityThread.java:151) 
         at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303) 
         at android.os.Handler.dispatchMessage(Handler.java:102) 
         at android.os.Looper.loop(Looper.java:135) 
         at android.app.ActivityThread.main(ActivityThread.java:5254) 
         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:903) 
         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698) 
        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.example.george.droidscanner.MainActivity.onCreate(MainActivity.java:43) 
         at android.app.Activity.performCreate(Activity.java:5990) 
         at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106) 
         at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2278) 
         at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)  
         at android.app.ActivityThread.access$800(ActivityThread.java:151)  
         at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)  
         at android.os.Handler.dispatchMessage(Handler.java:102)  
         at android.os.Looper.loop(Looper.java:135)  
         at android.app.ActivityThread.main(ActivityThread.java:5254)  
         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:903)  
         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)  
Application terminated.

來源

2017-02-13 miatech

自定義適配器nodelist.xml

那是你的問題本身。

setContentView(R.layout.activity_main);

您是findViewById -ing從activity_main.xml。那裏根本沒有ListView。

你可以試試這個activity_main

<include layout="@layout/nodelist" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent"/>

來源

2017-02-13 20:19:00

耶的代碼使用的是定製的適配器。但是使用自定義適配器執行此操作的正確方法是什麼？我是否需要使用單獨的視圖創建單獨的類，然後將自定義適配器列表視圖發佈到新視圖中？ – miatech

自定義適配器被添加到ListView中，它的佈局不包含ListView本身。除此之外，你從來沒有使用'nodelist.xml' ...你的適配器是由'android.R.layout.simple_list_item_1'製作的。 –

請參閱：https://guides.codepath.com/android/Using-an-ArrayAdapter-with -ListView＃using-a-custom-arrayadapter –

您的佈局文件裏不包含的ListView。所以findViewById(R.id.nodelist)返回null，你是空對象上設置適配器，因此它作爲呼喊

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference

來源

2017-02-13 20:26:17 Abilash

無法獲取在ip地址mac地址上運行的代碼

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