android命令模式IntentService 远程下载文件

服务可用在一下情景:

1,用户离开activity后,仍需要继续工作,例如从网络下载文件,播放音乐.

2,无论activity出现或离开,都需要持续工作,例如网络聊天应用.

3,连接网络服务,正在使用一个远程API提供的服务.

4,定时触发的任务

1.因为IntentService是Service子类,所以也需要在manifest中声明服务

<?xml version="1.0" encoding="utf-8"?>

<manifest xmlns:android="http://schemas.android.com/apk/res/android"

    package="com.example.intentservicedemo"

    android:versionCode="1"

    android:versionName="1.0" >

    <uses-sdk

        android:minSdkVersion="8"

        android:targetSdkVersion="21" />

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

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

    <application

        android:allowBackup="true"

        android:icon="@drawable/ic_launcher"

        android:label="@string/app_name"

        android:theme="@style/AppTheme" >

        <activity

            android:name=".MainActivity"

            android:label="@string/app_name" >

            <intent-filter>

                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />

            </intent-filter>

        </activity>

        <service android:name="com.example.intentservicedemo.ServiceDownloader"></service>

    </application>

</manifest>

2,新建 ServiceDownloader 继承自 IntentService

public class ServiceDownloader extends IntentService {

       //避免出现命名重复，将类的命名空间加在前面

    public static final String EXTRA_MESSAGER="com.wei.android.learning.ServiceDownloader.EXTRA_MESSAGER";

    public ServiceDownloader() {

        super("ServiceDownloader");

    }

    //命令模式的服务由client请求服务,

    private HttpClient client=null;

    int result ;

    private Intent mIntent;

    

    //client通过startService请求服务时,如果没有开启,则会首先执行onCreate(),在这里做一些初始化的工作,onCreate是在主线程中运行

    @Override

    public void onCreate() {

        super.onCreate();

        client=new DefaultHttpClient();

    }

    @Override

    public int onStartCommand(Intent intent, int flags, int startId) {

        return super.onStartCommand(intent, flags, startId);

        

    }

    //再收到客户端命令,处理完onStartCommand()后执行,onHandleIntent()是在后台线程中运行

    @Override

    protected void onHandleIntent(Intent i) {

        this.mIntent=i;

        result = Activity.RESULT_CANCELED; 

        HttpGet get=new HttpGet(i.getData().toString());

        ResponseHandler<byte[]> responseHandler =new ByteArrayResponseHandler();

        try {

            byte[] responseByte=client.execute(get,responseHandler);

            File output=new File(Environment.getExternalStorageDirectory(),i.getData().getLastPathSegment());

            if(output.exists()){

                output.delete();

            }

            FileOutputStream fos=new FileOutputStream(output.getPath());

            fos.write(responseByte);

            fos.close();

            result=Activity.RESULT_OK;

        } catch (ClientProtocolException e) {

            e.printStackTrace();

        } catch (IOException e) {

            e.printStackTrace();

        }

        Bundle extras=i.getExtras();

        if(extras!=null){

            Messenger messenger =(Messenger) extras.get(EXTRA_MESSAGER);

            Message msg=Message.obtain();

            msg.arg1=result;

            try {

                messenger.send(msg);

            } catch (RemoteException e) {

                e.printStackTrace();

            }

        }

    }

    

    @Override

    public void onDestroy() {

        Bundle extras=mIntent.getExtras();

        if(extras!=null){

            Messenger messenger =(Messenger) extras.get(EXTRA_MESSAGER);

            Message msg=Message.obtain();

            msg.arg1=result;

            try {

                messenger.send(msg);

            } catch (RemoteException e) {

                e.printStackTrace();

            }

        }

        client.getConnectionManager().shutdown();

        super.onDestroy();

    }

    

    private class ByteArrayResponseHandler implements ResponseHandler<byte[]>{

        @Override

        public byte[] handleResponse(HttpResponse response)

                throws ClientProtocolException, IOException {

            StatusLine statusLine=response.getStatusLine();

            if(statusLine.getStatusCode()>300){

                throw new HttpResponseException(statusLine.getStatusCode(),statusLine.getReasonPhrase()); 

            }

            HttpEntity entity=response.getEntity();

            if(entity==null){

                return null;

            }

            return EntityUtils.toByteArray(entity);

        }

    }

}

3,在客户端调用服务,开启下载任务,并且在下载完成时,可以收到下载完成的消息

public class MainActivity extends ActionBarActivity {

    

    Button btn_start;

    Button btn_stop;

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        btn_start=(Button) findViewById(R.id.btn_start);

        btn_stop=(Button) findViewById(R.id.btn_stop);

        btn_start.setOnClickListener(new OnClickListener() {

            @Override

            public void onClick(View v) {

                startDownLoader();

            }

        });

        btn_stop.setOnClickListener(new OnClickListener() {

            

            @Override

            public void onClick(View arg0) {

                stopDownLoader();

            }

        });

    }

    

    private void startDownLoader(){

        Intent intent=new Intent(this, ServiceDownloader.class);

        intent.setData(Uri.parse("http://commonsware.com/Android/excerpt.pdf")); 

        intent.putExtra(ServiceDownloader.EXTRA_MESSAGER,new Messenger(mh));

        startService(intent);

    }

    

    private Handler mh=new Handler(){

        @Override

        public void handleMessage(Message msg) {

            super.handleMessage(msg);

            //下载完成后,将取消服务按钮失效

            switch (msg.arg1) {

            case Activity.RESULT_OK:

                Toast.makeText(MainActivity.this, "Result : OK " , Toast.LENGTH_LONG).show();

                break;

            case Activity.RESULT_CANCELED:

                Toast.makeText(MainActivity.this, "Result : Cancel " , Toast.LENGTH_LONG).show();

                break;

            default:

                break;

            }

        }

    };

    private void stopDownLoader(){

        stopService(new Intent(this, ServiceDownloader.class));

    }

    

}

4,activity_main.xml

<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="com.example.intentservicedemo.MainActivity" >

    <Button 

        android:layout_width="fill_parent"

        android:layout_height="wrap_content"

        android:text="start"

        android:id="@+id/btn_start"

        />

    <Button 

        android:layout_width="fill_parent"

        android:layout_height="wrap_content"

        android:text="stop"

        android:id="@+id/btn_stop"

        />

</LinearLayout>

来自为知笔记(Wiz)