[Android Notification] Failed to post notification on channel & No Channel found for 原因是channelId不一致

问题：

使用 Notification 时，

1. Log 报错如下：

Line 5223: 03-07 11:49:20.121  1122  9346 E NotificationService: No Channel found for pkg=priv.xxx.demo, channelId=test, id=99, tag=null, opPkg=priv.xxx.demo, callingUid=10233, userId=0, incomingUserId=0, notificationUid=10233, notification=Notification(channel=test shortcut=null contentView=null vibrate=null sound=null defaults=0x0 flags=0x0 color=0x00000000 vis=PRIVATE)
    

2. 对应的 UI 提示：

Failed to post notification on channel "test". See log for more details.

分析

从Log和toast上看，应该是 channelId 一致性出了问题。

问题代码

public static void sendNotice(Context context) {
        Log.i(TAG, "[sendNotice] ENTER, context = " + context);
        NotificationManager notificationManager =
                (NotificationManager) context.getSystemService(Context.NOTIFICATION_SERVICE);

        // Android O  (8.0)新增的 API about channel。
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            // 使用NotificationChannel 类构建一个通知渠道
            NotificationChannel notificationChannel = new NotificationChannel("99", "TEMP",
                    NotificationManager.IMPORTANCE_DEFAULT);

            //通知的一些行为样式配置。
            notificationChannel.enableLights(true); //是否在launcher icon右上角展示提示点
            notificationChannel.setLightColor(Color.GREEN); //提示点颜色

            notificationManager.createNotificationChannel(notificationChannel);
        }
        Notification.Builder builder = new Notification.Builder(context,"test");
        builder.setContentTitle(context.getString(R.string.test_notification_title))
                .setContentText(context.getString(R.string.test_notification_content))
                .setWhen(System.currentTimeMillis())
                .setSmallIcon(R.mipmap.ic_launcher);
        Notification notification = builder.build();
        notificationManager.notify(99, notification);
}

问题解决

将channelId的内容统一，即问题代码中的“99”和“text”，取其一即可。

// channelId 要统一。
// channelId可以随便定义，只要保证全局唯一性就可以。
// 渠道名称是给用户看的，需要可以清楚地表达这个渠道的用途。
new NotificationChannel("99", "TEMP",
                    NotificationManager.IMPORTANCE_DEFAULT);
new Notification.Builder builder = new Notification.Builder(context,"99");

Nofitication 的用法

参考：通知概览  |  Android 开发者  |  Android Developers (google.cn)

1. 获取 NotificationManager 对通知进行管理
2. 构建一个通知渠道 NotificationChannel 
3. 通过 Builder 创建 Notification ，配置其内容。
4. 通过 manager 的notify() 显示通知

Note：关注 channelId 参数的统一

 public static void sendNotice(Context context, String channelId) {
        Log.i(TAG, "[sendNotice] ENTER, context = " + context);
        //1.获取 NotificationManager 对通知进行管理。
        NotificationManager notificationManager =
                (NotificationManager) context.getSystemService(Context.NOTIFICATION_SERVICE);
        //2.构建一个通知渠道 NotificationChannel。
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O && channelId != null) {
            NotificationChannel notificationChannel = new NotificationChannel(channelId, "TEMP",
                    NotificationManager.IMPORTANCE_DEFAULT);
            notificationManager.createNotificationChannel(notificationChannel);
        }
        //3.通过 Builder 创建 Notification ，配置其内容。
        Notification.Builder builder = new Notification.Builder(context, channelId);
        builder.setContentTitle(context.getString(R.string.test_notification_title))
                .setContentText(context.getString(R.string.test_notification_content))
                .setWhen(System.currentTimeMillis())
                .setSmallIcon(R.mipmap.ic_launcher);
        Notification notification = builder.build();
        //4.通过 manager 的notify() 显示通知。
        notificationManager.notify(1, notification);
    }

相关源码

NotificationChannel & Notification 的内部类 Builder

//android-30\android\app\NotificationChannel.java
    /**
     * Creates a notification channel.
     *
     * @param id The id of the channel. Must be unique per package. The value may be truncated if
     *           it is too long.
     * @param name The user visible name of the channel. You can rename this channel when the system
     *             locale changes by listening for the {@link Intent#ACTION_LOCALE_CHANGED}
     *             broadcast. The recommended maximum length is 40 characters; the value may be
     *             truncated if it is too long.
     * @param importance The importance of the channel. This controls how interruptive notifications
     *                   posted to this channel are.
     */
    public NotificationChannel(String id, CharSequence name, @Importance int importance) {
        this.mId = getTrimmedString(id);
        this.mName = name != null ? getTrimmedString(name.toString()) : null;
        this.mImportance = importance;
    }

// android-30\android\app\Notification.java
       /**
         * Constructs a new Builder with the defaults:
         *
         * @param context
         *            A {@link Context} that will be used by the Builder to construct the
         *            RemoteViews. The Context will not be held past the lifetime of this Builder
         *            object.
         * @param channelId
         *            The constructed Notification will be posted on this
         *            {@link NotificationChannel}. To use a NotificationChannel, it must first be
         *            created using {@link NotificationManager#createNotificationChannel}.
         */
        public Builder(Context context, String channelId) {
            this(context, (Notification) null);
            mN.mChannelId = channelId;
        }

Other

很多教程指导都是罗列方法和代码使用案例，缺少一些关键注意点的指引。

我这样的小白有点按部就班的不解，有些坑就是新手才会碰到的。