Android 通知チャンネルを有効にしているかどうか判定する

check-if-specific-channel-enabled.md

https://stackoverflow.com/questions/46928874/android-oreo-notifications-check-if-specific-channel-enabled

if (!notificationManager.areNotificationsEnabled()) {
        openNotificationSettings();
        return;
}

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O &&
        isChannelBlocked(CHANNEL_1_ID)) {
    openChannelSettings(CHANNEL_1_ID);
    return;
}

private void openNotificationSettings() {
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
        Intent intent = new Intent(Settings.ACTION_APP_NOTIFICATION_SETTINGS);
        intent.putExtra(Settings.EXTRA_APP_PACKAGE, getPackageName());
        startActivity(intent);
    } else {
        Intent intent = new Intent(Settings.ACTION_APPLICATION_DETAILS_SETTINGS);
        intent.setData(Uri.parse("package:" + getPackageName()));
        startActivity(intent);
    }
}

@RequiresApi(26)
private boolean isChannelBlocked(String channelId) {
    NotificationManager manager = getSystemService(NotificationManager.class);
    NotificationChannel channel = manager.getNotificationChannel(channelId);

    return channel != null &&
            channel.getImportance() == NotificationManager.IMPORTANCE_NONE;
}

@RequiresApi(26)
private void openChannelSettings(String channelId) {
    Intent intent = new Intent(Settings.ACTION_CHANNEL_NOTIFICATION_SETTINGS);
    intent.putExtra(Settings.EXTRA_APP_PACKAGE, getPackageName());
    intent.putExtra(Settings.EXTRA_CHANNEL_ID, channelId);
    startActivity(intent);
}