关于通知是否显示角标
应用发通知时，可以设置是否显示徽章：
设置接口：channel.setShowBadge(true); 修改为false既不显示。
411 private void createNotificationChannel() {
412 Log.d(TAG, "createNotificationChannel");
413 if (mNotificationManager == null) {
414 mNotificationManager = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
415 if (android.os.Build.VERSION.SDK_INT >= 26) {
416 String nameChannel = getString(R.string.app_name);
417 NotificationChannel channel;
418 channel = new NotificationChannel(CHANNEL_ID, nameChannel, NotificationManager.IMPORTANCE_LOW);
419 channel.setShowBadge(true);
420 channel.enableLights(false);
421 channel.enableVibration(false);
422 mNotificationManager.createNotificationChannel(channel);
423 }
424 }
425 }
构造 NotificationRankingUpdate获取：
frameworks/base/services/core/java/com/android/server/notification/NotificationManagerService.java#makeRankingUpdateLocked
6242 showBadge.putBoolean(key, record.canShowBadge());
看看源码，当创建通知channel时：
frameworks/base/services/core/java/com/android/server/notification/RankingHelper.java
609 @Override
610 public void createNotificationChannel(String pkg, int uid, NotificationChannel channel,
611 boolean fromTargetApp, boolean hasDndAccess) {
612 Preconditions.checkNotNull(pkg);
613 Preconditions.checkNotNull(channel);
614 Preconditions.checkNotNull(channel.getId());
615 Preconditions.checkArgument(!TextUtils.isEmpty(channel.getName()));
616 Record r = getOrCreateRecord(pkg, uid);getOrCreateRecord创建app通知channel record。
如可以adb pull data/system/notification_policy.xml看看：
创建了三个channel id，第一个设置不显示徽章，第二三个显示，show_badge="true"
这个XML是怎么保存的？
frameworks/base/services/core/java/com/android/server/notification/NotificationManagerService.java
void readPolicyXml(InputStream stream, boolean forRestore)
将从XML读取通知记录
private void writePolicyXml(OutputStream stream, boolean forBackup)
将把通知数据写入到XML
这个XML文件怎么创建？
是在onStart()的调用init()函数，入参：
final File systemDir = new File(Environment.getDataDirectory(), "system");
new AtomicFile(new File(systemDir, "notification_policy.xml"), "notification-policy"),
在/RankingHelper.java的
public void writeXml(XmlSerializer out, boolean forBackup)
方法中，将会调用NotificationChannel的writeXml，将具体channel id的信息写入到xml
/frameworks/base/core/java/android/app/NotificationChannel.java
697 private void writeXml(XmlSerializer out, boolean forBackup, @Nullable Context context)
698 throws IOException {
699 Preconditions.checkArgument(!forBackup || context != null,
700 "forBackup is true but got null context");
701 out.startTag(null, TAG_CHANNEL);
702 out.attribute(null, ATT_ID, getId());
703 if (getName() != null) {
704 out.attribute(null, ATT_NAME, getName().toString());
705 }
706 if (getDescription() != null) {
707 out.attribute(null, ATT_DESC, getDescription());
708 }
709 if (getImportance() != DEFAULT_IMPORTANCE) {
710 out.attribute(
711 null, ATT_IMPORTANCE, Integer.toString(getImportance()));
712 }
749 if (canShowBadge()) {
750 out.attribute(null, ATT_SHOW_BADGE, Boolean.toString(canShowBadge()));
751 }
761
762 out.endTag(null, TAG_CHANNEL);
763 }
764