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  • Android（java）学习笔记57：PC and Phone 通信程序

    1. 首先我写的程序代码如下：

     1 package com.himi.udpsend;
 2 
 3 import java.net.DatagramPacket;
 4 import java.net.DatagramSocket;
 5 import java.net.DatagramSocketImpl;
 6 import java.net.InetAddress;
 7 import java.net.SocketException;
 8 import java.net.UnknownHostException;
 9 
10 import android.app.Activity;
11 import android.content.Context;
12 import android.net.wifi.WifiInfo;
13 import android.net.wifi.WifiManager;
14 import android.os.Bundle;
15 import android.util.Log;
16 import android.view.View;
17 import android.view.View.OnClickListener;
18 import android.widget.Button;
19 import android.widget.EditText;
20 
21 
22 public class MainActivity extends Activity implements OnClickListener {
23     private EditText edittext;
24     private Button  btnsend;
25     private WifiInfo wifiInfo; //类Wifiinfo，WifiInfo获取各种Wifi各种信息
26     @Override
27     protected void onCreate(Bundle savedInstanceState) {
28         super.onCreate(savedInstanceState);
29         setContentView(R.layout.activity_main);
30         
31         edittext = (EditText)findViewById(R.id.edit);
32         btnsend = (Button)findViewById(R.id.btnsend);
33         
34         btnsend.setOnClickListener(this);
35         
36         WifiManager wman = (WifiManager) getSystemService(Context.WIFI_SERVICE);
37         
38         if(! wman.isWifiEnabled()) {
39             wman.setWifiEnabled(true);
40         }
41         Log.e("ip", intToIp(wifiInfo.getIpAddress()));//获得本机ip
42         
43     }
44     
45     
46     public String intToIp(int i) {
47         return (i & 0xff) +"."+
48           ((i>>8) & 0xff )+"."+
49           ((i>>16) & 0xff )+"."+
50           ((i>>24) & 0xff );
51                 
52     }
53 
54 
55 
56 
57     public void onClick(View v) {
58 
59         try {
60             // 创建发送端socket对象
61             DatagramSocket ds = new DatagramSocket();
62 
63             // 创建数据并打包
64             String edit_content = edittext.getText().toString();
65             byte[] bys = edit_content.getBytes();
66             int length = bys.length;
67 
68             String ip = intToIp(wifiInfo.getIpAddress());
69             InetAddress hostip = InetAddress.getByName(ip);
70             
71             int port = 10086;
72             DatagramPacket dp = new DatagramPacket(bys, length, hostip, port);
73             
74             //发送数据包
75             ds.send(dp);
76             //关闭套接字，回收资源
77             ds.close();
78 
79         } catch (Exception e) {
80             // TODO 自动生成的 catch 块
81             e.printStackTrace();
82         }
83         
84         
85     }
86 
87 
88     
89     
90 }

    2. 报错如下：

    06-26 02:37:29.270: E/Trace(841): error opening trace file: No such file or directory (2)
06-26 02:37:30.400: D/AndroidRuntime(841): Shutting down VM
06-26 02:37:30.400: W/dalvikvm(841): threadid=1: thread exiting with uncaught exception (group=0x40a71930)
06-26 02:37:30.540: E/AndroidRuntime(841): FATAL EXCEPTION: main
06-26 02:37:30.540: E/AndroidRuntime(841): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.himi.udpsend/com.himi.udpsend.MainActivity}: java.lang.NullPointerException
06-26 02:37:30.540: E/AndroidRuntime(841):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
06-26 02:37:30.540: E/AndroidRuntime(841):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
06-26 02:37:30.540: E/AndroidRuntime(841):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
06-26 02:37:30.540: E/AndroidRuntime(841):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
06-26 02:37:30.540: E/AndroidRuntime(841):     at android.os.Handler.dispatchMessage(Handler.java:99)
06-26 02:37:30.540: E/AndroidRuntime(841):     at android.os.Looper.loop(Looper.java:137)
06-26 02:37:30.540: E/AndroidRuntime(841):     at android.app.ActivityThread.main(ActivityThread.java:5041)
06-26 02:37:30.540: E/AndroidRuntime(841):     at java.lang.reflect.Method.invokeNative(Native Method)
06-26 02:37:30.540: E/AndroidRuntime(841):     at java.lang.reflect.Method.invoke(Method.java:511)
06-26 02:37:30.540: E/AndroidRuntime(841):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
06-26 02:37:30.540: E/AndroidRuntime(841):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
06-26 02:37:30.540: E/AndroidRuntime(841):     at dalvik.system.NativeStart.main(Native Method)
06-26 02:37:30.540: E/AndroidRuntime(841): Caused by: java.lang.NullPointerException
06-26 02:37:30.540: E/AndroidRuntime(841):     at com.himi.udpsend.MainActivity.onCreate(MainActivity.java:41)
06-26 02:37:30.540: E/AndroidRuntime(841):     at android.app.Activity.performCreate(Activity.java:5104)
06-26 02:37:30.540: E/AndroidRuntime(841):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
06-26 02:37:30.540: E/AndroidRuntime(841):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
06-26 02:37:30.540: E/AndroidRuntime(841):     ... 11 more
06-26 02:37:34.910: I/Process(841): Sending signal. PID: 841 SIG: 9

    原因：空指针异常，这时就要查看自己的程序中是否存在空指针。

    4. 解决办法是：

     1 package com.himi.udpsend;
 2 
 3 import java.net.DatagramPacket;
 4 import java.net.DatagramSocket;
 5 import java.net.DatagramSocketImpl;
 6 import java.net.InetAddress;
 7 import java.net.SocketException;
 8 import java.net.UnknownHostException;
 9 
10 import android.app.Activity;
11 import android.content.Context;
12 import android.net.wifi.WifiInfo;
13 import android.net.wifi.WifiManager;
14 import android.os.Bundle;
15 import android.util.Log;
16 import android.view.View;
17 import android.view.View.OnClickListener;
18 import android.widget.Button;
19 import android.widget.EditText;
20 
21 
22 public class MainActivity extends Activity implements OnClickListener {
23     private EditText edittext;
24     private Button  btnsend;
25     private WifiInfo wifiInfo; 
26     @Override
27     protected void onCreate(Bundle savedInstanceState) {
28         super.onCreate(savedInstanceState);
29         setContentView(R.layout.activity_main);
30         
31         edittext = (EditText)findViewById(R.id.edit);
32         btnsend = (Button)findViewById(R.id.btnsend);
33         
34         btnsend.setOnClickListener(this);
35         
36         WifiManager wman = (WifiManager) getSystemService(Context.WIFI_SERVICE);
37         
38         if(! wman.isWifiEnabled()) {
39             wman.setWifiEnabled(true);
40         }//没有正确使用Log（）
41         //Log.e("ip", intToIp(wifiInfo.getIpAddress()));//获得本机ip
42         
43     }
44     
45     
46     public String intToIp(int i) {
47         return (i & 0xff) +"."+
48           ((i>>8) & 0xff )+"."+
49           ((i>>16) & 0xff )+"."+
50           ((i>>24) & 0xff );
51                 
52     }
53 
54 
55 
56 
57     public void onClick(View v) {
58 
59         try {
60             // 创建发送端socket对象
61             DatagramSocket ds = new DatagramSocket();
62 
63             // 创建数据并打包
64             String edit_content = edittext.getText().toString();
65             byte[] bys = edit_content.getBytes();
66             int length = bys.length;
67 
68             String ip = intToIp(wifiInfo.getIpAddress());
69             InetAddress hostip = InetAddress.getByName(ip);
70             
71             int port = 10086;
72             DatagramPacket dp = new DatagramPacket(bys, length, hostip, port);
73             
74             //发送数据包
75             ds.send(dp);
76             //关闭套接字，回收资源
77             ds.close();
78 
79         } catch (Exception e) {
80             // TODO 自动生成的 catch 块
81             e.printStackTrace();
82         }
83         
84         
85     }
86 
87 
88     
89     
90 }

    附加：

    DatagramSocket：套接字用来UDP通信

    DatagramPacket：用来包装UDP通信数据包

    InetAddress：是Java对IP地址的封装
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  • 原文地址：https://www.cnblogs.com/hebao0514/p/4601914.html
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