我对android开发很陌生，我正在尝试开发一个服务器客户端应用程序，其中服务器是一个简单的Java应用程序，它从文件中读取一些文本并使用输出流发送它。客户端是一个Android应用程序，在单击按钮时读取此流并将其显示在文本视图上。
我在ADK中使用eclipse，并在模拟器上测试两个代码的样子：
服务器：
import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.UnknownHostException;
public class Server {
/**
* @param args
* @throws IOException
* @throws UnknownHostException
*/
public static void main(String[] args) throws UnknownHostException, IOException
{
System.out.println("***********Starting ***********");
ServerSocket servsock = new ServerSocket(12344);
System.out.println("Waiting...");
Socket sock = servsock.accept();
while (true)
{
System.out.println("Accepted connection : " + sock);
File myFile = new File ("source.txt");
while (true){
byte [] mybytearray = new byte [(int)myFile.length()];
FileInputStream fis = new FileInputStream(myFile);
BufferedInputStream bis = new BufferedInputStream(fis);
bis.read(mybytearray,0,mybytearray.length);
OutputStream os = sock.getOutputStream();
System.out.println("Sending...");
os.write(mybytearray,0,mybytearray.length);
os.flush();
}
}
}
}
客户：
-MainActivity
package com.example.streamerclient;
import android.app.Activity;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
public class MainActivity extends Activity implements OnClickListener {
Button ConnectBtn ;
@Override
public void onResume() {
super.onResume();
//setContentView(R.layout.activity_main);
System.out.println(" on resume ");
ConnectBtn = (Button)findViewById(R.id.ConnectButton);
ConnectBtn.setOnClickListener(this);
}
@Override
public void onPause() {
super.onPause();
}
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
Connecting c = new Connecting();
}
}
- 连接班级
package com.example.streamerclient;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.net.Socket;
import android.app.Activity;
import android.widget.TextView;
public class Connecting extends Activity implements Runnable
{
private Socket sock;
private BufferedReader r;
private BufferedWriter out;
TextView Data;
public Connecting ()
{
Data = (TextView) findViewById(R.id.DataTextView);
Thread th = new Thread(this);
th.start();
}
@Override
public void run() {
try
{
System.out.println("trying to initiated ");
Data.setText("trying to initiated ");
sock = new Socket("10.0.2.2",12344);
System.out.println(" socket initiated ");
Data.setText(" socket initiated ");
r = new BufferedReader(new InputStreamReader(sock.getInputStream()));
Data.setText(" buffer reader initiated ");
System.out.println(" buffer reader initiated ");
out = new BufferedWriter(new OutputStreamWriter(sock.getOutputStream()));
Data.setText(" buffer writer initiated ");
System.out.println(" buffer writer initiated ");
final String data = r.readLine();
Data.setText(" Data read is: \n"+data);
System.out.println(" Data read is: \n"+data);
}
catch (IOException ioe) { }
}
public void OnPause()
{
System.out.println(" paused");
try {
if (sock != null) {
sock.getOutputStream().close();
sock.getInputStream().close();
sock.close();
System.out.println(" everything is closed ");
}
} catch (IOException e) {}
}
}
我知道我知道，代码的某些部分没有被使用..我的下一个任务是让这个应用程序向服务器发送命令......所以我还在试验。
在模拟器上运行应用程序时，它甚至会在显示任何GUI组件之前停止。知道为什么吗？这是日志文件的内容
03-17 08:16:30.886: W/Trace(846): Unexpected value from nativeGetEnabledTags: 0
03-17 08:16:30.886: W/Trace(846): Unexpected value from nativeGetEnabledTags: 0
03-17 08:16:30.886: W/Trace(846): Unexpected value from nativeGetEnabledTags: 0
03-17 08:16:31.016: W/Trace(846): Unexpected value from nativeGetEnabledTags: 0
03-17 08:16:31.016: W/Trace(846): Unexpected value from nativeGetEnabledTags: 0
03-17 08:16:31.126: I/System.out(846): on resume
03-17 08:16:31.447: D/AndroidRuntime(846): Shutting down VM
03-17 08:16:31.447: W/dalvikvm(846): threadid=1: thread exiting with uncaught exception (group=0x40a70930)
03-17 08:16:31.457: E/AndroidRuntime(846): FATAL EXCEPTION: main
03-17 08:16:31.457: E/AndroidRuntime(846): java.lang.RuntimeException: Unable to resume activity {com.example.streamerclient/com.example.streamerclient.MainActivity}: java.lang.NullPointerException
03-17 08:16:31.457: E/AndroidRuntime(846): at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2742)
03-17 08:16:31.457: E/AndroidRuntime(846): at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2771)
03-17 08:16:31.457: E/AndroidRuntime(846): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2235)
03-17 08:16:31.457: E/AndroidRuntime(846): at android.app.ActivityThread.access$600(ActivityThread.java:141)
03-17 08:16:31.457: E/AndroidRuntime(846): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
03-17 08:16:31.457: E/AndroidRuntime(846): at android.os.Handler.dispatchMessage(Handler.java:99)
03-17 08:16:31.457: E/AndroidRuntime(846): at android.os.Looper.loop(Looper.java:137)
03-17 08:16:31.457: E/AndroidRuntime(846): at android.app.ActivityThread.main(ActivityThread.java:5039)
03-17 08:16:31.457: E/AndroidRuntime(846): at java.lang.reflect.Method.invokeNative(Native Method)
03-17 08:16:31.457: E/AndroidRuntime(846): at java.lang.reflect.Method.invoke(Method.java:511)
03-17 08:16:31.457: E/AndroidRuntime(846): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
03-17 08:16:31.457: E/AndroidRuntime(846): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
03-17 08:16:31.457: E/AndroidRuntime(846): at dalvik.system.NativeStart.main(Native Method)
03-17 08:16:31.457: E/AndroidRuntime(846): Caused by: java.lang.NullPointerException
03-17 08:16:31.457: E/AndroidRuntime(846): at com.example.streamerclient.MainActivity.onResume(MainActivity.java:20)
03-17 08:16:31.457: E/AndroidRuntime(846): at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1185)
03-17 08:16:31.457: E/AndroidRuntime(846): at android.app.Activity.performResume(Activity.java:5182)
03-17 08:16:31.457: E/AndroidRuntime(846): at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2732)
03-17 08:16:31.457: E/AndroidRuntime(846): ... 12 more
谢谢！
答案 0 :(得分：0)
尝试将整个onResume（）的内容移动到onCreate（）方法。始终在onCreate（）中进行UI设置。请阅读：Activity Lifecycle Management。
并进一步查询stackoverflow：）
干杯！
答案 1 :(得分：0)
您在MainActivity的第20行遇到NullPointerException，检查该行 我认为这个问题更适合stackoverflow