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;
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 }
时间： 2024-10-07 00:33:25