1、Android O(8.0)通知的改变

NotificationChannel是android8.0新增的特性，如果App的targetSDKVersion>=26，没有设置channel通知渠道的话，就会导致通知无法展示。

Android O 引入了 通知渠道（Notification Channels），以提供统一的系统来帮助用户管理通知，如果是针对 android O 为目标平台时，必须实现一个或者多个通知渠道，以向用户显示通知。比如聊天软件，为每个聊天组设置一个通知渠道，指定特定声音、灯光等配置。

2、Android Channel通知的兼容支配

创建NotificationChannel

1. 创建NotificationChannel对象，指定Channel的id、name和通知的重要程度
2. 使用NotificationMannager的createNotificationChannel方法来添加Channel。

 private NotificationManager getNotificationManager() {
        if (mNotificationManager == null) {
            mNotificationManager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
        }
        return mNotificationManager;
  }

    @NonNull
    private NotificationCompat.Builder getNotificationBuilder() {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            NotificationChannel channel = new NotificationChannel("channel_id", "channel_name",
                    NotificationManager.IMPORTANCE_DEFAULT);
            //是否绕过请勿打扰模式
            channel.canBypassDnd();
            //闪光灯
            channel.enableLights(true);
            //锁屏显示通知
            channel.setLockscreenVisibility(VISIBILITY_SECRET);
            //闪关灯的灯光颜色
            channel.setLightColor(Color.RED);
            //桌面launcher的消息角标
            channel.canShowBadge();
            //是否允许震动
            channel.enableVibration(true);
            //获取系统通知响铃声音的配置
            channel.getAudioAttributes();
            //获取通知取到组
            channel.getGroup();
            //设置可绕过  请勿打扰模式
            channel.setBypassDnd(true);
            //设置震动模式
            channel.setVibrationPattern(new long[]{100, 100, 200});
            //是否会有灯光
            channel.shouldShowLights();
            getNotificationManager().createNotificationChannel(channel);
        }
        NotificationCompat.Builder notification = new NotificationCompat.Builder(this, "channel_id");
        notification.setContentTitle("新消息来了");
        notification.setContentText("周末到了，不用上班了");
        notification.setSmallIcon(R.mipmap.ic_launcher);
        notification.setAutoCancel(true);
        return notification;
    }

1. 设置通知重要性级别
   该级别必须要在 NotificationChannel 的构造函数中指定，总共要五个级别；范围是从 NotificationManager.IMPORTANCE_NONE(0) ~ NotificationManager.IMPORTANCE_HIGH(4)
   ，如果要支持 Android 7.1（API 25）及以下的设备，还得调用NotificationCompat 的 setPriority 方法来设置，如下所示

builder.setPriority(NotificationCompat.PRIORITY_DEFAULT);

Android 8.0 及以上是使用NotificationManager.IMPORTANCE_，Android 7.1 及以下是使用NotificationCompat.PRIORITY_它们都是定义的常量；下面我们以表格的形式更好的展示出来。

上面这些通知级别用户都是可以在 Channel 设置中更改

3、Android Channel通知的应用与管理（更新、删除）

4、自定义Channel通知栏

 private void sendCustomNotification() {
        NotificationCompat.Builder builder = getNotificationBuilder();
        RemoteViews remoteViews = new RemoteViews(getPackageName(), R.layout.layout_custom_notifition);
        remoteViews.setTextViewText(R.id.notification_title, "custom_title");
        remoteViews.setTextViewText(R.id.notification_content, "custom_content");

        Intent intent = new Intent(this, MainActivity.class);
        PendingIntent pendingIntent = PendingIntent.getActivity(this, -1,
                intent, PendingIntent.FLAG_UPDATE_CURRENT);
        remoteViews.setOnClickPendingIntent(R.id.turn_next, pendingIntent);
        builder.setCustomContentView(remoteViews);
        getNotificationManager().notify(3, builder.build());
    }

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
                android:layout_width="match_parent"
                android:layout_height="match_parent">

    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="vertical">

        <TextView
            android:id="@+id/notification_title"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="通知栏标题"
            android:textSize="24sp"/>

        <TextView
            android:id="@+id/notification_content"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="通知栏内容"/>

    </LinearLayout>

    <Button
        android:id="@+id/turn_next"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentRight="true"
        android:text="跳转"/>
</RelativeLayout>

5、封装的代码

public class NotificationUtils extends ContextWrapper {

    public static final String CHANNEL_ID = "default";
    private static final String CHANNEL_NAME = "Default Channel";
    private static final String CHANNEL_DESCRIPTION = "this is default channel!";
    private NotificationManager mManager;

    public NotificationUtils(Context base) {
        super(base);
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            createNotificationChannel();
        }
    }

    @TargetApi(Build.VERSION_CODES.O)
    private void createNotificationChannel() {
        NotificationChannel channel = new NotificationChannel(CHANNEL_ID, CHANNEL_NAME, NotificationManager.IMPORTANCE_DEFAULT);
       //是否绕过请勿打扰模式
        channel.canBypassDnd();
        //闪光灯
        channel.enableLights(true);
        //锁屏显示通知
        channel.setLockscreenVisibility(VISIBILITY_SECRET);
        //闪关灯的灯光颜色
        channel.setLightColor(Color.RED);
        //桌面launcher的消息角标
        channel.canShowBadge();
        //是否允许震动
        channel.enableVibration(true);
        //获取系统通知响铃声音的配置
        channel.getAudioAttributes();
        //获取通知取到组
        channel.getGroup();
        //设置可绕过  请勿打扰模式
        channel.setBypassDnd(true);
        //设置震动模式
        channel.setVibrationPattern(new long[]{100, 100, 200});
        //是否会有灯光
        channel.shouldShowLights();
        getManager().createNotificationChannel(channel);
    }

    private NotificationManager getManager() {
        if (mManager == null) {
            mManager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
        }
        return mManager;
    }

   /**
     * 发送通知
     */
    public void sendNotification(String title, String content) {
        NotificationCompat.Builder builder = getNotification(title, content);
        getManager().notify(1, builder.build());
    }

    private NotificationCompat.Builder getNotification(String title, String content) {
        NotificationCompat.Builder builder = null;
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            builder = new NotificationCompat.Builder(getApplicationContext(), CHANNEL_ID);
        } else {
            builder = new NotificationCompat.Builder(getApplicationContext());
            builder.setPriority(PRIORITY_DEFAULT);
        }
        //标题
        builder.setContentTitle(title);
        //文本内容
        builder.setContentText(content);
        //小图标
        builder.setSmallIcon(R.mipmap.ic_launcher);
        //设置点击信息后自动清除通知
        builder.setAutoCancel(true);
        return builder;
    }

    /**
     * 发送通知
     */
    public void sendNotification(int notifyId, String title, String content) {
        NotificationCompat.Builder builder = getNotification(title, content);
        getManager().notify(notifyId, builder.build());
    }

    /**
     * 发送带有进度的通知
     */
    public void sendNotificationProgress(String title, String content, int progress, PendingIntent intent) {
        NotificationCompat.Builder builder = getNotificationProgress(title, content, progress, intent);
        getManager().notify(0, builder.build());
    }

    /**
     * 获取带有进度的Notification
     */
    private NotificationCompat.Builder getNotificationProgress(String title, String content,
                                                               int progress, PendingIntent intent) {
        NotificationCompat.Builder builder = null;
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            builder = new NotificationCompat.Builder(getApplicationContext(), CHANNEL_ID);
        } else {
            builder = new NotificationCompat.Builder(getApplicationContext());
            builder.setPriority(PRIORITY_DEFAULT);
        }
        //标题
        builder.setContentTitle(title);
        //文本内容
        builder.setContentText(content);
        //小图标
        builder.setSmallIcon(R.mipmap.ic_launcher);
        //设置大图标，未设置时使用小图标代替，拉下通知栏显示的那个图标
        //设置大图片 BitmpFactory.decodeResource(Resource res,int id) 根据给定的资源Id解析成位图
        builder.setLargeIcon(BitmapFactory.decodeResource(getResources(), R.mipmap.ic_launcher));
        if (progress > 0 && progress < 100) {
            //一种是有进度刻度的（false）,一种是循环流动的（true）
            //设置为false，表示刻度，设置为true，表示流动
            builder.setProgress(100, progress, false);
        } else {
            //0,0,false,可以将进度条隐藏
            builder.setProgress(0, 0, false);
            builder.setContentText("下载完成");
        }
        //设置点击信息后自动清除通知
        builder.setAutoCancel(true);
        //通知的时间
        builder.setWhen(System.currentTimeMillis());
        //设置点击信息后的跳转（意图）
        builder.setContentIntent(intent);
        return builder;
    }
}