<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity" >

    <LinearLayout 
        android:layout_width="match_parent"
        android:layout_height="wrap_content" 
        android:orientation="horizontal" >

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:gravity="center"
            android:text="城市："
            android:textSize="23sp" />

        <EditText 
            android:id="@+id/city"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_weight="3"
            android:inputType="text" />
    </LinearLayout>

    <Button
        android:id="@+id/query"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" 
        android:text="查询" 
        android:textSize="23sp" />
    
    <TextView
        android:id="@+id/result"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />
</LinearLayout>

package com.rainsong.handlerdemo;

import java.io.IOException;
import java.net.URLEncoder;
import java.util.ArrayList;

import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.message.BasicNameValuePair;
import org.apache.http.util.EntityUtils;

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends Activity {
    private static final String JUHE_URL_ENVIRONMENT_AIR_PM = 
                                    "http://web.juhe.cn:8080/environment/air/pm";
    private static final String JUHE_APPKEY = "你申请的APPKEY值";

    private static final int MSG_SUCCESS = 0;
    private static final int MSG_FAILURE = 1;

    EditText et_city;
    Button btn_query;
    TextView tv_result;
    String city;

    private Handler mHandler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            switch(msg.what) {
            case MSG_SUCCESS:
                tv_result.setText((String)msg.obj);
                break;
            case MSG_FAILURE:
                Toast.makeText(MainActivity.this, "查询失败",
                                    Toast.LENGTH_LONG).show();
                tv_result.setText("");
                break;
            }
        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        et_city = (EditText)findViewById(R.id.city);
        tv_result = (TextView)findViewById(R.id.result);
        btn_query = (Button)findViewById(R.id.query);

        btn_query.setOnClickListener(new OnClickListener() {
            public void onClick(View view) {
                city = et_city.getText().toString();
                if (city.length() < 1) {
                    Toast.makeText(MainActivity.this, "请输入城市名",
                            Toast.LENGTH_LONG).show();
                    tv_result.setText("");
                    return;
                }
                
                new Thread() {
                    public void run() {
                        ArrayList<NameValuePair> headerList = new ArrayList<NameValuePair>();
                        headerList.add(new BasicNameValuePair("Content-Type", "text/html; charset=utf-8"));

                        String targetUrl = JUHE_URL_ENVIRONMENT_AIR_PM;

                        ArrayList<NameValuePair> paramList = new ArrayList<NameValuePair>();
                        paramList.add(new BasicNameValuePair("key", JUHE_APPKEY));
                        paramList.add(new BasicNameValuePair("dtype", "json"));
                        paramList.add(new BasicNameValuePair("city", city));

                        for (int i = 0; i < paramList.size(); i++) {
                            NameValuePair nowPair = paramList.get(i);
                            String value = http://www.mamicode.com/nowPair.getValue();>
API知识点
public class
Handler
extends Object

android.os.Handler

Class Overview
A Handler allows you to send and process Message and Runnable objects associated with a thread‘s MessageQueue. Each Handler instance is associated with a single thread and that thread‘s message queue. When you create a new Handler, it is bound to the thread / message queue of the thread that is creating it -- from that point on, it will deliver messages and runnables to that message queue and execute them as they come out of the message queue.

Public Constructors
Handler()
Default constructor associates this handler with the Looper for the current thread.

void handleMessage(Message msg)
Subclasses must implement this to receive messages.

final Message obtainMessage()
Returns a new Message from the global message pool.

final Message obtainMessage(int what, Object obj)
Same as obtainMessage(), except that it also sets the what and obj members of the returned Message.

public final class
Message
extends Object
implements Parcelable

android.os.Message

Class Overview
Defines a message containing a description and arbitrary data object that can be sent to a Handler. This object contains two extra int fields and an extra object field that allow you to not do allocations in many cases.

void sendToTarget()
Sends this Message to the Handler specified by getTarget().


Android Handler消息机制