Android 开发 - 为什么这个应用程序会崩溃？答案

【问题标题】：Android Development - Why is this application crashing?Android 开发 - 为什么这个应用程序会崩溃？
【发布时间】：2014-02-24 20:50:05
【问题描述】：

我制作了一个小型 Android 应用程序，它会在您打开它时发送一个 UDP 数据包。

问题是，当你打开它时它崩溃了，而不是发送数据包。

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

代码如下：

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

那么为什么会崩溃呢？代码在我看来很好，很奇怪。

【问题讨论】：

请使用 stacktrace 发布您的 logcat 输出。
好的，添加了 logcat 输出。
确保您在清单中声明了互联网权限。

标签： android sockets networking udp packet

【解决方案1】：

看起来您正试图在 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来实现网络操作，特别是ASyncTask 关于这方面的问题和示例确实有 1000 多个。

这里有一个tutorial 可以帮助您入门

同时为您的清单添加必要的权限

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

【讨论】：

谢谢，试试（只是添加权限不行）。

【解决方案2】：

您很可能在您的 android 清单文件中缺少 INTERNET 权限。在<application> 标签内添加这一行：

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

【讨论】：

谢谢，但它仍然崩溃。将尝试创建另一个线程，如 Or 建议。还是谢谢。