Question

我做了一个小型的Android应用程序，在你打开它的那一刻发送一个UDP数据包。

问题是，当你打开它时它会崩溃，而不是发送数据包。

我的意思是，我已经尝试在Eclipse的Android虚拟设备上运行它，它在那里崩溃了。

以下是代码：

package com.example.messagesender;

import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.app.Activity;

import java.io.*;
import java.net.*;

public class Message_Sender extends Activity {
    DatagramSocket clientSocket;
    InetAddress IPAddressx;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_message__sender);
        try {
            clientSocket = new DatagramSocket();
        } catch (SocketException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
          try {
            IPAddressx = InetAddress.getByName("127.0.0.1");
        } catch (UnknownHostException e) {
            e.printStackTrace();
        }
          byte[] sendData = new byte[1024];
          String sentence = "Hello World!";
          sendData = sentence.getBytes();
          DatagramPacket sendPacket = new DatagramPacket(sendData, sendData.length, IPAddressx, 12345);
          try {
            clientSocket.send(sendPacket);
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.message__sender, menu);
        return true;
    }

}

Logcat输出：

01-31 19:00:58.420: W/System.err(810): java.net.SocketException: socket failed: EACCES (Permission denied)
01-31 19:00:58.420: W/System.err(810):  at libcore.io.IoBridge.socket(IoBridge.java:576)
01-31 19:00:58.420: W/System.err(810):  at java.net.PlainDatagramSocketImpl.create(PlainDatagramSocketImpl.java:91)
01-31 19:00:58.420: W/System.err(810):  at java.net.DatagramSocket.createSocket(DatagramSocket.java:133)
01-31 19:00:58.540: W/System.err(810):  at java.net.DatagramSocket.<init>(DatagramSocket.java:80)
01-31 19:00:58.540: W/System.err(810):  at java.net.DatagramSocket.<init>(DatagramSocket.java:65)
01-31 19:00:58.540: W/System.err(810):  at com.example.messagesender.Message_Sender.onCreate(Message_Sender.java:23)
01-31 19:00:58.540: W/System.err(810):  at android.app.Activity.performCreate(Activity.java:5231)
01-31 19:00:58.540: W/System.err(810):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
01-31 19:00:58.540: W/System.err(810):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
01-31 19:00:58.540: W/System.err(810):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
01-31 19:00:58.540: W/System.err(810):  at android.app.ActivityThread.access$800(ActivityThread.java:135)
01-31 19:00:58.540: W/System.err(810):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
01-31 19:00:58.540: W/System.err(810):  at android.os.Handler.dispatchMessage(Handler.java:102)
01-31 19:00:58.540: W/System.err(810):  at android.os.Looper.loop(Looper.java:136)
01-31 19:00:58.590: W/System.err(810):  at android.app.ActivityThread.main(ActivityThread.java:5017)
01-31 19:00:58.590: W/System.err(810):  at java.lang.reflect.Method.invokeNative(Native Method)
01-31 19:00:58.590: W/System.err(810):  at java.lang.reflect.Method.invoke(Method.java:515)
01-31 19:00:58.590: W/System.err(810):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
01-31 19:00:58.590: W/System.err(810):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
01-31 19:00:58.590: W/System.err(810):  at dalvik.system.NativeStart.main(Native Method)
01-31 19:00:58.590: W/System.err(810): Caused by: libcore.io.ErrnoException: socket failed: EACCES (Permission denied)
01-31 19:00:58.610: W/System.err(810):  at libcore.io.Posix.socket(Native Method)
01-31 19:00:58.610: W/System.err(810):  at libcore.io.BlockGuardOs.socket(BlockGuardOs.java:181)
01-31 19:00:58.610: W/System.err(810):  at libcore.io.IoBridge.socket(IoBridge.java:561)
01-31 19:00:58.610: W/System.err(810):  ... 19 more
01-31 19:00:58.630: D/AndroidRuntime(810): Shutting down VM
01-31 19:00:58.630: W/dalvikvm(810): threadid=1: thread exiting with uncaught exception (group=0xb1a86ba8)
01-31 19:00:58.640: E/AndroidRuntime(810): FATAL EXCEPTION: main
01-31 19:00:58.640: E/AndroidRuntime(810): Process: com.example.messagesender, PID: 810
01-31 19:00:58.640: E/AndroidRuntime(810): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.messagesender/com.example.messagesender.Message_Sender}: java.lang.NullPointerException
01-31 19:00:58.640: E/AndroidRuntime(810):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
01-31 19:00:58.640: E/AndroidRuntime(810):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
01-31 19:00:58.640: E/AndroidRuntime(810):  at android.app.ActivityThread.access$800(ActivityThread.java:135)
01-31 19:00:58.640: E/AndroidRuntime(810):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
01-31 19:00:58.640: E/AndroidRuntime(810):  at android.os.Handler.dispatchMessage(Handler.java:102)
01-31 19:00:58.640: E/AndroidRuntime(810):  at android.os.Looper.loop(Looper.java:136)
01-31 19:00:58.640: E/AndroidRuntime(810):  at android.app.ActivityThread.main(ActivityThread.java:5017)
01-31 19:00:58.640: E/AndroidRuntime(810):  at java.lang.reflect.Method.invokeNative(Native Method)
01-31 19:00:58.640: E/AndroidRuntime(810):  at java.lang.reflect.Method.invoke(Method.java:515)
01-31 19:00:58.640: E/AndroidRuntime(810):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
01-31 19:00:58.640: E/AndroidRuntime(810):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
01-31 19:00:58.640: E/AndroidRuntime(810):  at dalvik.system.NativeStart.main(Native Method)
01-31 19:00:58.640: E/AndroidRuntime(810): Caused by: java.lang.NullPointerException
01-31 19:00:58.640: E/AndroidRuntime(810):  at com.example.messagesender.Message_Sender.onCreate(Message_Sender.java:38)
01-31 19:00:58.640: E/AndroidRuntime(810):  at android.app.Activity.performCreate(Activity.java:5231)
01-31 19:00:58.640: E/AndroidRuntime(810):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
01-31 19:00:58.640: E/AndroidRuntime(810):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
01-31 19:00:58.640: E/AndroidRuntime(810):  ... 11 more

那为什么会崩溃呢？代码看起来很好，这很奇怪。

Answer 1

看起来你正试图在UI线程上进行网络调用，这是一个很大的禁忌。

看看如何使用后台线程实现网络操作，特别是ASyncTask关于这一点，有1000个问题和例子。

这是一个tutorial，可以帮助您入门

还为清单添加必要的权限

<uses-permission android:name="android.permission.INTERNET" />

Answer 2

您最有可能错过Android清单文件中的INTERNET权限。在<application>代码中添加此行：

<uses-permission android:name="android.permission.INTERNET"/>

Android开发 - 为什么这个应用程序崩溃了？

2 个答案: