服务几乎都是在后台运行的，移植依赖它都是默默的做着辛苦的工作，但是服务的优先级还是比较低的，当系统出现内存不足的情况时，就有可能会回收掉正在后天运行的服务。如果你希望服务可以一直保持运行状态，而不会由于内存不足的原因导致被回收，就可以考虑使用前台服务。前台服务和普通服务的最大区别就在于，它会一直有一个正在运行的图标在系统的状态栏显示，下拉状态栏后可以看到更加详细的信息，非常类似于通知灯额效果。当然有时候你也可能不仅仅是为了防止服务被回收掉才使用前台服务的，有些项目由于特殊的需求会要求必须使用前台服务，比如说彩云天气这款天气预报应用，它额的服务在后台更新天气数据的同时，还会在系统的状态栏一直显示当前的天气信息。
一、修改activity_main.xml文件
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
android:orientation="vertical"
android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">
<Button
android:id="@+id/start_service"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Start Service"/>
<Button
android:id="@+id/stop_service"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Stop Service"/>
<Button
android:id="@+id/bind_service"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Bind Service"/>
<Button
android:id="@+id/unbind_service"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Unbind Service"/>
</LinearLayout>
二、修改MainActivity文件
package com.example.yxp.service;
import android.app.Activity;
import android.content.ComponentName;
import android.content.Intent;
import android.content.ServiceConnection;
import android.os.Bundle;
import android.os.IBinder;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import java.sql.BatchUpdateException;
public class MainActivity extends Activity {
private MyService.DownloadBinder downloadBinder;
private ServiceConnection connection = new ServiceConnection() {
@Override
public void onServiceConnected(ComponentName name, IBinder service) {
downloadBinder = (MyService.DownloadBinder) service;
downloadBinder.startDownload();
downloadBinder.getProgress();
}
@Override
public void onServiceDisconnected(ComponentName componentName) {
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final Button startService = (Button) findViewById(R.id.start_service);
Button stopService = (Button) findViewById(R.id.stop_service);
startService.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Intent startIntent = new Intent(MainActivity.this,MyService.class);
startService(startIntent);
}
});
stopService.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Intent stopIntent = new Intent(MainActivity.this,MyService.class);
stopService(stopIntent);
}
});
final Button bindService = (Button) findViewById(R.id.bind_service);
final Button unbindService = (Button) findViewById(R.id.unbind_service);
bindService.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Intent bindIntent = new Intent(MainActivity.this,MyService.class);
bindService(bindIntent,connection,BIND_AUTO_CREATE);
}
});
unbindService.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
unbindService(connection);
}
});
}
}
三、修改MyService文件
package com.example.yxp.service;
import android.app.Notification;
import android.app.PendingIntent;
import android.app.Service;
import android.content.Intent;
import android.graphics.BitmapFactory;
import android.os.Binder;
import android.os.IBinder;
import android.util.Log;
public class MyService extends Service {
private DownloadBinder mBinder = new DownloadBinder();
class DownloadBinder extends Binder {
public void startDownload(){
Log.d("MyService","startDownload executed");
}
public int getProgress(){
Log.d("MyService","getProgress executed");
return 0;
}
}
public IBinder onBind(Intent intent){
return mBinder;
}
public MyService() {
}
public void onCreate(){
super.onCreate();
Log.d("MyService","onCreate executed");
Intent intent = new Intent(this,MainActivity.class);
PendingIntent pi = PendingIntent.getActivity(this,0,intent,0);
Notification notification = new Notification.Builder(this)
.setContentTitle("This is content title")
.setContentText("This is content text")
.setWhen(System.currentTimeMillis())
.setSmallIcon(R.mipmap.ic_launcher)
.setLargeIcon(BitmapFactory.decodeResource(getResources(),R.mipmap.ic_launcher))
.setContentIntent(pi)
.build();
startForeground(1,notification);
}
public int onStartCommand(Intent intent,int flags,int startId){
Log.d("MyService","onStartCommand executed");
return super.onStartCommand(intent,flags,startId);
}
public void onDestroy(){
super.onDestroy();
Log.d("MyService", "onDestroy executed");
}
}
四、效果
`···································
