安卓下建立socket就崩溃，分到子线程仍然不行，求助啊

Question

原代码如下，如果我不用BUTTON去触发的话是可以建立SOCKET的，但是用上BUTTON，把建立SOCKET的方法放到子线程中，仍然exception会显示不能再主线程中使用网络操作，真心求解为什么，看了2天了，刚学JAVA，不太理解。
package com.example.xlguang.wifi;

import android.os.Bundle;
import android.os.Handler;
import android.support.v7.app.ActionBarActivity;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

import java.io.IOException;
import java.net.Socket;
import java.net.UnknownHostException;

public class MainActivity extends ActionBarActivity {
private EditText editText;
private Button button;
private TextView MTextview;
Handler handler=new Handler();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
editText = (EditText)findViewById(R.id.editText1);
button = (Button)findViewById(R.id.button1);
final RunnableThread runnable = new RunnableThread();
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {

        handler.post(runnable);
        }
    });



}

public class RunnableThread implements Runnable
{
public void run() {

        Socket socket = null;
          String message = editText.getText().toString()+ "\r\n" ;
        try {

            //创建客户端socket,注意:不能用localhost或127.0.0.1，Android模拟器把自己作为localhost
            socket = new Socket("172.16.5.30",8000);

            PrintWriter out = new PrintWriter(new BufferedWriter(new OutputStreamWriter
                    (socket.getOutputStream())),true);
            //发送数据
               out.println(message);

            //接收数据
                        BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
                        String msg = in.readLine();
                        if (null != msg){
                            editText.setText(msg);
                            System.out.println(msg);
                        }
                        else{
                            editText.setText("data error");
                        }
             out.close();
              in.close();
        } catch (UnknownHostException e) {
               e.printStackTrace();
        }
        catch (IOException e) {
             e.printStackTrace();
        }
        finally{
            try {
                if (null != socket){
                    socket.close();
                }
            } catch (IOException e) {
                  e.printStackTrace();
            }
        }

}
}

Answer 1

 handler.post(runnable);  //这是运行在UI线程中的，android会把runnable放到UI线程的消息循环中进行分支处理

所以改成

 new Thread(runnable).start();