Hey there! Let's troubleshoot why your notification's left-side icon isn't showing up—this is a super common gotcha when starting out with Android notifications, so I’ve got a few key things to check:

The icon that appears on the left of notifications is set with the setSmallIcon() method on your NotificationCompat.Builder object. It’s easy to mix this up with setLargeIcon() (which adds a bigger icon on the right in most Android versions).

Double-check your notification builder code includes this line:

NotificationCompat.Builder builder = new NotificationCompat.Builder(this, YOUR_CHANNEL_ID)
        .setSmallIcon(R.drawable.your_notification_icon) // This is the left-side icon
        .setContentTitle("Your Notification Title")
        .setContentText("Your notification content");

If you skipped setSmallIcon() or used the wrong method, that’s almost certainly why the icon is missing.

Starting with Android 5.0 (API 21), notification small icons must be single-color (white) with a transparent background. If you’re using a colorful icon, the system will either tint it to white (if you’re lucky) or hide it completely.

The easiest fix is to use Android Studio’s built-in tool to generate a compliant icon:

• Right-click your res/drawable folder → New → Image Asset
• Select "Notification Icons" as the asset type
• Follow the wizard to create a properly formatted icon—this ensures it works across all Android versions.

It’s easy to slip up here, so verify:

• The icon filename in R.drawable.your_notification_icon is spelled correctly (Android resource names are case-sensitive!)
• The icon file exists in the res/drawable directory (or use a vector drawable here for density-independent support)
• You haven’t only placed the icon in a density-specific folder (like drawable-hdpi)—without copies in other density folders, some devices won’t load it.

If you’re targeting Android 8.0 (API 26) or higher, you need to create a notification channel before posting any notifications. Even if you set the icon correctly, missing this step can cause odd behavior like icons not showing.

Add this method to your MainActivity and call it in onCreate():

private void createNotificationChannel() {
    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
        CharSequence channelName = getString(R.string.notification_channel_name);
        String channelDesc = getString(R.string.notification_channel_desc);
        int importance = NotificationManager.IMPORTANCE_DEFAULT;
        
        NotificationChannel channel = new NotificationChannel("YOUR_CHANNEL_ID", channelName, importance);
        channel.setDescription(channelDesc);
        
        NotificationManager notificationManager = getSystemService(NotificationManager.class);
        notificationManager.createNotificationChannel(channel);
    }
}

Give these steps a try—chances are one of them will fix your missing icon issue!

内容的提问来源于stack exchange，提问作者Bob liao