android學習筆記四——Service

service是運行後臺的一段代碼，並且和Activity不同，它不能直接和用戶交互，也不能自行啓動，對於service來說，主要用於在後臺運行，比方說後臺下載，後臺播放音樂等，和Activity一樣於oncreate後創建，ondestroy後銷燬，一個service的啓動有兩種方式，一種是Context.StartService的方式來啓動，這種方式啓動服務後，該服務就和啓動程序毫無關聯了，只有在調用context.stopservice後，或者服務自行死亡後，該服務纔會被銷燬，第二種是通過Context.bindservice的方式綁定程序後啓動服務，此時服務就和改程序綁定在一起了，當該程序死亡時服務也會被終結掉，這就是服務的基本概念
下面來介紹下服務的使用方式

1、首先要繼承Service類並重寫其中的onStart，onDestroy,onbind,onunbind,oncreate這幾個方法

public class MyService extends Service {
    //定義log的標籤
    private static final String str="ServiceDemo";
    private Mybind binder=new Mybind();
    @Override
    public IBinder onBind(Intent intent) {
        // TODO Auto-generated method stub
        Log.i(str,"start bind service");
        return binder;
    }
    @Override
    public void onCreate() {
        // TODO Auto-generated method stub
        Log.i(str,"start create service");
        super.onCreate();
    }
    @Override
    public void onDestroy() {
        // TODO Auto-generated method stub
        Log.i(str,"start destroy service");
        super.onDestroy();
    }
    @SuppressWarnings("deprecation")
    @Override
    public void onStart(Intent intent, int startId) {
        // TODO Auto-generated method stub
        Log.i(str,"start service");
        super.onStart(intent, startId);
    }
    @Override
    public boolean onUnbind(Intent intent) {
        // TODO Auto-generated method stub
        Log.i(str,"start unbind service");
        return super.onUnbind(intent);
    }
    //此方法是爲了可以在Acitity中獲得服務的實例  
    public class Mybind extends Binder{
        MyService getService(){
            return MyService.this;
        }
    }

}

2.在入口程序中註冊服務<service android:name=".MyService"></service>

3.使用startService或是bindService啓動服務
（1）通過startservice啓用服務時，android會首先調用oncreate方法創建服務，之後調用onstart啓用服務，在調用stopservice結束服務時會自行調用ondestroy銷燬服務，需要注意的是在服務被創建後，多次調用startservice並不會重複調用oncreate，除非服務銷燬後，但多次調用startservice會多次調用onstart

（2）通過bindservice啓用服務時，android會首先調用oncreate方法創建服務，之後調用onbind啓用綁定服務，在調用unbindservice結束服務時會先調用onunbind解除綁定，在調用ondestroy銷燬服務，需要注意的是在服務被創建後，多次調用bindservice並不會重複調用oncreate和onbind，除非該服務被銷燬
下面重點介紹一下bindservice的啓用方式
bindService一共有三個參數第一個參數爲意圖，第二個服務連接狀態，第三個爲標誌

第一個參數的主要目的是爲了定義要啓動哪個服務，第二個參數就是指示連接該服務狀態，第三個參數是定義其進行的方式

既然是第一個參數是intent，就需要先定義一個意圖參數即
Intent intent=new Intent();然後和Activity一樣通過setClass來指定要啓動的服務
intent.setClass(ServiceDemo.this,MyService.class);

第二個參數是爲了指示連接該服務狀態

  private ServiceConnection conn=new ServiceConnection(){

        @Override
        //在連接成功時調用
        public void onServiceConnected(ComponentName arg0, IBinder arg1) {
            // TODO Auto-generated method stub
            Log.i("ServiceDemo","connected Service");
        }

        @Override
        //在服務連接失敗時調用
        public void onServiceDisconnected(ComponentName arg0) {
            // TODO Auto-generated method stub
            Log.i("ServiceDemo","disconnected Service");
        }

    };

所以完整的調用方式如下

    Intent intent=new Intent();
    intent.setClass(ServiceDemo.this,MyService.class);
    private ServiceConnection conn=new ServiceConnection(){

        @Override
        //在連接成功時調用
        public void onServiceConnected(ComponentName arg0, IBinder arg1) {
            // TODO Auto-generated method stub
            Log.i("ServiceDemo","connected Service");
        }

        @Override
        //在服務連接失敗時調用
        public void onServiceDisconnected(ComponentName arg0) {
            // TODO Auto-generated method stub
            Log.i("ServiceDemo","disconnected Service");
        }

    };

    mcontext.bindService(intent, conn, Context.BIND_AUTO_CREATE);

下面是一個方便理解服務進行過程的例子，提供了兩種不同啓用方式，本文中並沒有介紹兩種啓動方式複合運用的場景，也可以通過下面的程序自行理解

servicedemo.Activity

package com.example.ui_demo;

import android.app.Activity;
import android.content.ComponentName;
import android.content.Context;
import android.content.Intent;
import android.content.ServiceConnection;
import android.os.Bundle;
import android.os.IBinder;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;

public class ServiceDemo extends Activity {
    private MyService mservice;
    private Button mButtonstart;
    private Button mButtonstop;
    private Button mButtonexit;
    private Button mButtonbind;
    private Button mButtonbindstop;
    private Context mcontext;
    private ServiceConnection conn=new ServiceConnection(){

        @Override
        public void onServiceConnected(ComponentName arg0, IBinder arg1) {
            // TODO Auto-generated method stub
            Log.i("ServiceDemo","connected Service");
        }

        @Override
        public void onServiceDisconnected(ComponentName arg0) {
            // TODO Auto-generated method stub
            Log.i("ServiceDemo","disconnected Service");
        }

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

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.service_demo, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }
    public void setup(){
        mcontext=ServiceDemo.this;
        mButtonstart=(Button) this.findViewById(R.id.startservice);
        mButtonstop=(Button) this.findViewById(R.id.stopservice);
        mButtonexit=(Button) this.findViewById(R.id.exitservice);
        mButtonbind=(Button) this.findViewById(R.id.bindservice);
        mButtonbindstop=(Button) this.findViewById(R.id.stopbindservice);
        Mybutton mbutton=new Mybutton();
        mButtonstart.setOnClickListener(mbutton);
        mButtonstop.setOnClickListener(mbutton);
        mButtonexit.setOnClickListener(mbutton);
        mButtonbind.setOnClickListener(mbutton);
        mButtonbindstop.setOnClickListener(mbutton);
    }
    public class Mybutton implements OnClickListener{
        @Override
        public void onClick(View vi ) {
            // TODO Auto-generated method stub
            if(vi==mButtonstart){
                Intent intent=new Intent();
                intent.setClass(ServiceDemo.this,MyService.class);
                mcontext.startService(intent);
            }else if(vi==mButtonstop){
                Intent intent=new Intent();
                intent.setClass(ServiceDemo.this,MyService.class);
                mcontext.stopService(intent);
            }else if(vi==mButtonexit){
                ServiceDemo.this.finish();
            }else if(vi==mButtonbind){
                Intent intent=new Intent();
                intent.setClass(ServiceDemo.this,MyService.class);
                mcontext.bindService(intent, conn, Context.BIND_AUTO_CREATE);
            }else if(vi==mButtonbindstop){
                mcontext.unbindService(conn);
            }

        }

    }

}

action_servicedemo.xml

<RelativeLayout 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:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.ui_demo.ServiceDemo" >

    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hello_world" />

    <TableLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" >
    <TableRow>

    <Button
        android:id="@+id/startservice"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignRight="@+id/stopservice"
        android:layout_below="@+id/stopservice"
        android:layout_column="1"
        android:layout_marginTop="16dp"
        android:text="啓用服務"
        android:textSize="20sp" />

    </TableRow>
    <TableRow>

        <Button
            android:id="@+id/stopservice"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_column="1"
            android:layout_marginTop="24dp"
            android:text="停止服務"
            android:textSize="20sp" />

    </TableRow>
     <TableRow>

        <Button
            android:id="@+id/bindservice"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_column="1"
            android:layout_marginTop="24dp"
            android:text="啓動綁定服務"
            android:textSize="20sp" />

    </TableRow>
     <TableRow>

        <Button
            android:id="@+id/stopbindservice"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_column="1"
            android:layout_marginTop="24dp"
            android:text="停止綁定服務"
            android:textSize="20sp" />

    </TableRow>
      <TableRow>

        <Button
            android:id="@+id/exitservice"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_column="1"
            android:layout_marginTop="24dp"
            android:text="退出"
            android:textSize="20sp" />

    </TableRow>
     </TableLayout> 
</RelativeLayout>

MyService.java

package com.example.ui_demo;

import android.app.Service;
import android.content.Intent;
import android.os.Binder;
import android.os.IBinder;
import android.util.Log;

public class MyService extends Service {
    //定義log的標籤
    private static final String str="ServiceDemo";
    private Mybind binder=new Mybind();
    @Override
    public IBinder onBind(Intent intent) {
        // TODO Auto-generated method stub
        Log.i(str,"start bind service");
        return binder;
    }
    @Override
    public void onCreate() {
        // TODO Auto-generated method stub
        Log.i(str,"start create service");
        super.onCreate();
    }
    @Override
    public void onDestroy() {
        // TODO Auto-generated method stub
        Log.i(str,"start destroy service");
        super.onDestroy();
    }
    @SuppressWarnings("deprecation")
    @Override
    public void onStart(Intent intent, int startId) {
        // TODO Auto-generated method stub
        Log.i(str,"start service");
        super.onStart(intent, startId);
    }
    @Override
    public boolean onUnbind(Intent intent) {
        // TODO Auto-generated method stub
        Log.i(str,"start unbind service");
        return super.onUnbind(intent);
    }
    public class Mybind extends Binder{
        MyService getService(){
            return MyService.this;
        }
    }

}