关于疯狂android讲义里面的示例

package org.crazyit.net;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.List;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.HttpClient;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.message.BasicNameValuePair;
import org.apache.http.protocol.HTTP;
import org.apache.http.util.EntityUtils;
import android.app.Activity;
import android.app.AlertDialog;
import android.content.DialogInterface;
import android.os.Bundle;
import android.os.Handler;
import android.os.Looper;
import android.os.Message;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
/**
* Description:
* <br/>site: <a href=”http://www.crazyit.org”>crazyit.org</a>
* <br/>Copyright (C), 2001-2014, Yeeku.H.Lee
* <br/>This program is protected by copyright laws.
* <br/>Program Name:
* <br/>Date:
* @author  Yeeku.H.Lee kongyeeku@163.com
* @version  1.0
*/
public class HttpClientTest extends Activity
{
TextView response;
HttpClient httpClient;
Handler handler = new Handler()
{
public void handleMessage(Message msg)
{
if(msg.what == 0x123)
{
// 使用response文本框显示服务器响应
response.append(msg.obj.toString() + “\n”);
}
}
};
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
// 创建DefaultHttpClient对象
httpClient = new DefaultHttpClient();
response = (TextView) findViewById(R.id.response);
}
public void accessSecret(View v)
{
response.setText(“”);
new Thread()
{
@Override
public void run()
{
// 创建一个HttpGet对象
HttpGet get = new HttpGet(
“http://192.168.1.88:8888/foo/secret.jsp”);  //①
try
{
// 发送GET请求
HttpResponse httpResponse = httpClient.execute(get);//②
HttpEntity entity = httpResponse.getEntity();
if (entity != null)
{
// 读取服务器响应
BufferedReader br = new BufferedReader(
new InputStreamReader(entity.getContent()));
String line = null;
while ((line = br.readLine()) != null)
{
Message msg = new Message();
msg.what = 0x123;
msg.obj = line;
handler.sendMessage(msg);
}
}
}
catch (Exception e)
{
e.printStackTrace();
}
}
}.start();
}
public void showLogin(View v)
{
// 加载登录界面
final View loginDialog = getLayoutInflater().inflate(
R.layout.login, null);
// 使用对话框供用户登录系统
new AlertDialog.Builder(HttpClientTest.this)
.setTitle(“登录系统”)
.setView(loginDialog)
.setPositiveButton(“登录”,
new DialogInterface.OnClickListener()
{
@Override
public void onClick(DialogInterface dialog,
int which)
{
// 获取用户输入的用户名、密码
final String name = ((EditText) loginDialog
.findViewById(R.id.name)).getText()
.toString();
final String pass = ((EditText) loginDialog
.findViewById(R.id.pass)).getText()
.toString();
new Thread()
{
@Override
public void run()
{
try
{
HttpPost post = new HttpPost(“http://192.168”
+ “.1.88:8888/foo/login.jsp”);//③
// 假如传递参数个数比较多的话可以对传递的参数进行封装
List<NameValuePair> params = new
ArrayList<NameValuePair>();
params.add(new BasicNameValuePair
(“name”, name));
params.add(new BasicNameValuePair
(“pass”, pass));
// 设置请求参数
post.setEntity(new UrlEncodedFormEntity(
params, HTTP.UTF_8));
// 发送POST请求
HttpResponse response = httpClient
.execute(post);  //④
// 假如服务器成功地返回响应
if (response.getStatusLine()
.getStatusCode() == 200)
{
String msg = EntityUtils
.toString(response.getEntity());
Looper.prepare();
// 提示登录成功
Toast.makeText(HttpClientTest.this,
msg, Toast.LENGTH_SHORT).show();
Looper.loop();
}
}
catch (Exception e)
{
e.printStackTrace();
}
}
}.start();
}
}).setNegativeButton(“取消”, null).show();
}
}
上面是疯狂android讲义第二版606页关于httpClient类的示例
最后这里为何调用   Looper.prepare(); 和 Looper.loop(); 启动消息循环？
String msg = EntityUtils
.toString(response.getEntity());
Looper.prepare();
// 提示登录成功
Toast.makeText(HttpClientTest.this,
msg, Toast.LENGTH_SHORT).show();
Looper.loop();