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;
}
}

}