android学习笔记四——Service

service是运行后台的一段代码，并且和Activity不同，它不能直接和用户交互，也不能自行启动，对于service来说，主要用于在后台运行，比方说后台下载，后台播放音乐等，和Activity一样于oncreate后创建，ondestroy后销毁，一个service的启动有两种方式，一种是Context.StartService的方式来启动，这种方式启动服务后，该服务就和启动程序毫无关联了，只有在调用context.stopservice后，或者服务自行死亡后，该服务才会被销毁，第二种是通过Context.bindservice的方式绑定程序后启动服务，此时服务就和改程序绑定在一起了，当该程序死亡时服务也会被终结掉，这就是服务的基本概念
下面来介绍下服务的使用方式

1、首先要继承Service类并重写其中的onStart，onDestroy,onbind,onunbind,oncreate这几个方法

public class MyService extends Service {
    //定义log的标签
    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);
    }
    //此方法是为了可以在Acitity中获得服务的实例  
    public class Mybind extends Binder{
        MyService getService(){
            return MyService.this;
        }
    }

}

2.在入口程序中注册服务<service android:name=".MyService"></service>

3.使用startService或是bindService启动服务
（1）通过startservice启用服务时，android会首先调用oncreate方法创建服务，之后调用onstart启用服务，在调用stopservice结束服务时会自行调用ondestroy销毁服务，需要注意的是在服务被创建后，多次调用startservice并不会重复调用oncreate，除非服务销毁后，但多次调用startservice会多次调用onstart

（2）通过bindservice启用服务时，android会首先调用oncreate方法创建服务，之后调用onbind启用绑定服务，在调用unbindservice结束服务时会先调用onunbind解除绑定，在调用ondestroy销毁服务，需要注意的是在服务被创建后，多次调用bindservice并不会重复调用oncreate和onbind，除非该服务被销毁
下面重点介绍一下bindservice的启用方式
bindService一共有三个参数第一个参数为意图，第二个服务连接状态，第三个为标志

第一个参数的主要目的是为了定义要启动哪个服务，第二个参数就是指示连接该服务状态，第三个参数是定义其进行的方式

既然是第一个参数是intent，就需要先定义一个意图参数即
Intent intent=new Intent();然后和Activity一样通过setClass来指定要启动的服务
intent.setClass(ServiceDemo.this,MyService.class);

第二个参数是为了指示连接该服务状态

  private ServiceConnection conn=new ServiceConnection(){

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

        @Override
        //在服务连接失败时调用
        public void onServiceDisconnected(ComponentName arg0) {
            // TODO Auto-generated method stub
            Log.i("ServiceDemo","disconnected Service");
        }

    };

所以完整的调用方式如下

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

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

        @Override
        //在服务连接失败时调用
        public void onServiceDisconnected(ComponentName arg0) {
            // TODO Auto-generated method stub
            Log.i("ServiceDemo","disconnected Service");
        }

    };

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

下面是一个方便理解服务进行过程的例子，提供了两种不同启用方式，本文中并没有介绍两种启动方式复合运用的场景，也可以通过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="启用服务"
        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="停止服务"
            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="启动绑定服务"
            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="停止绑定服务"
            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 {
    //定义log的标签
    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;
        }
    }

}