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法律学如何在服务中实现前台启动？
在进入示例之前，我们应该了解 Android 中的服务是什么。服务将在后台运行而无需与 UI 交互，即使 Activity 被销毁后它仍然工作。
此示例演示如何在服务中实现前台启动。
步骤 1 - 在 Android Studio 中创建一个新项目，转到 文件 ⇒ 新建项目，并填写所有必需的详细信息以创建新项目。
步骤 2 - 将以下代码添加到 res/layout/activity_main.xml。
<?xml version = "1.0" encoding = "utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android = "http://schemas.android.com/apk/res/android"
xmlns:app = "http://schemas.android.com/apk/res-auto"
xmlns:tools = "http://schemas.android.com/tools"
android:layout_width = "match_parent"
android:layout_height = "match_parent"
tools:context = ".MainActivity">
<TextView
android:id = "@+id/text"
android:layout_width = "wrap_content"
android:layout_height = "wrap_content"
android:text = "Start Service"
android:textSize = "25sp"
app:layout_constraintBottom_toBottomOf = "parent"
app:layout_constraintLeft_toLeftOf = "parent"
app:layout_constraintRight_toRightOf = "parent"
app:layout_constraintTop_toTopOf = "parent" />
</android.support.constraint.ConstraintLayout>在上面的代码中，我们使用了 TextView，当用户点击 TextView 时，它将启动 startForeground()。
步骤 3 - 将以下代码添加到 src/MainActivity.java
package com.example.andy.myapplication;
import android.app.ActivityManager;
import android.content.Context;
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.TextView;
public class MainActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final TextView text = findViewById(R.id.text);
text.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
if (isMyServiceRunning(service.class)) {
text.setText("Stoped");
stopService(new Intent(MainActivity.this, service.class));
} else {
text.setText("Started");
startService(new Intent(MainActivity.this, service.class));
}
}
});
}
private boolean isMyServiceRunning(Class<?> serviceClass) {
ActivityManager manager = (ActivityManager) getSystemService(Context.ACTIVITY_SERVICE);
for (ActivityManager.RunningServiceInfo service : manager.getRunningServices(Integer.MAX_VALUE)) {
if (serviceClass.getName().equals(service.service.getClassName())) {
return true;
}
}
return false;
}
}在上面的代码中，启动和停止服务。我们使用了 Intent 并传递了上下文和服务类。现在在包文件夹中创建一个服务类作为 service.class 并添加以下代码 -
package com.example.andy.myapplication;
import android.annotation.TargetApi;
import android.app.Notification;
import android.app.NotificationChannel;
import android.app.NotificationManager;
import android.app.PendingIntent;
import android.app.Service;
import android.content.Context;
import android.content.Intent;
import android.graphics.Color;
import android.media.MediaPlayer;
import android.os.Build;
import android.os.IBinder;
import android.support.annotation.RequiresApi;
import android.support.v4.app.NotificationCompat;
import android.widget.Toast;
public class service extends Service {
@Override
public IBinder onBind(Intent intent) {
return null;
}
@Override
public void onCreate() {
super.onCreate();
}
@TargetApi(Build.VERSION_CODES.O)
@RequiresApi(api = Build.VERSION_CODES.JELLY_BEAN)
@Override
public int onStartCommand(Intent intent, int flags, int startId) {
Toast.makeText(this, "Notification Service started by user.", Toast.LENGTH_LONG).show();
String NOTIFICATION_CHANNEL_ID = "com.example.andy.myapplication";
String channelName = "My Background Service";
NotificationChannel chan = new NotificationChannel(NOTIFICATION_CHANNEL_ID, channelName, NotificationManager.IMPORTANCE_NONE);
chan.setLightColor(Color.BLUE);
chan.setLockscreenVisibility(Notification.VISIBILITY_PRIVATE);
NotificationManager manager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
assert manager != null;
manager.createNotificationChannel(chan);
Intent notificationIntent = new Intent(this, MainActivity.class);
PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, notificationIntent, 0);
Notification notification = new Notification.Builder(this,NOTIFICATION_CHANNEL_ID)
.setSmallIcon(R.mipmap.ic_launcher)
.setContentTitle("My Awesome App")
.setContentIntent(pendingIntent).build();
startForeground(1337, notification);
return START_STICKY;
}
@RequiresApi(api = Build.VERSION_CODES.N)
@Override
public void onDestroy() {
super.onDestroy();
stopForeground(true);
Toast.makeText(this, "Notification Service destroyed by user.", Toast.LENGTH_LONG).show();
}
}在上面的代码中，我们使用了通知通道和通知构建器，如下所示 -
String NOTIFICATION_CHANNEL_ID = "com.example.andy.myapplication";
String channelName = "My Background Service";
NotificationChannel chan = new NotificationChannel(NOTIFICATION_CHANNEL_ID, channelName, NotificationManager.IMPORTANCE_NONE);
chan.setLightColor(Color.BLUE);
chan.setLockscreenVisibility(Notification.VISIBILITY_PRIVATE);
NotificationManager manager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
assert manager != null;
manager.createNotificationChannel(chan);
Intent notificationIntent = new Intent(this, MainActivity.class);
PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, notificationIntent, 0);
Notification notification = new Notification.Builder(this,NOTIFICATION_CHANNEL_ID)
.setSmallIcon(R.mipmap.ic_launcher)
.setContentTitle("My Awesome App")
.setContentIntent(pendingIntent).build();
startForeground(1337, notification);要启动和停止前台服务，请使用以下代码 -
startForeground(1337, notification); stopForeground(true);
步骤 4 - 将以下代码添加到 manifest.xml
<?xml version = "1.0" encoding = "utf-8"?>
<manifest xmlns:android = "http://schemas.android.com/apk/res/android"
package = "com.example.andy.myapplication">
<application
android:allowBackup = "true"
android:icon = "@mipmap/ic_launcher"
android:label = "@string/app_name"
android:roundIcon = "@mipmap/ic_launcher_round"
android:supportsRtl = "true"
android:theme = "@style/AppTheme">
<activity android:name = ".MainActivity">
<intent-filter>
<action android:name = "android.intent.action.MAIN" />
<category android:name = "android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<service android:name = ".service"/>
</application>
</manifest>让我们尝试运行您的应用程序。我假设您已将您的实际 Android 移动设备连接到您的计算机。要从 Android Studio 运行应用程序，请打开您的项目之一的 Activity 文件，然后单击工具栏中的运行 
图标。选择您的移动设备作为选项，然后检查您的移动设备，它将显示您的默认屏幕 -
以上结果是初始屏幕，点击 TextView，它将启动通知服务，如下所示 -
在上面的结果中，服务已启动，现在点击 TextView，它将停止通知服务，如下所示 -
点击 此处 下载项目代码
更新于: 2019-07-30
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