The small icon of notification setting shows a small square

Method 1 （ Modify the size and size of the icon ） （ Invalid ）：

NotificationCompat.Builder mBuilder = new NotificationCompat.Builder(this)
   .setSmallIcon(R.drawable.abc)
   .setContentTitle("aaaaa")
   .setContentText("bbbbbb")
   .setLargeIcon(abcd);

Called setSmallIcon() Method , But the small icon in the notification bar is a square , Not the icon we set ;

solve ： The icon size is limited to 20kb within . （ Invalid ）

Troubleshooting skills ：

When the icon set is too large ,AndroidStudio The picture doesn't show up when previewing ;

  Change to a small icon to display normally ：

The small icon of this phone can show , But it's gray , It's not colored .（ It's not completely solved ） 

Method 2 （ It works ）：
Use different icons in different versions , stay android 8.0 following , Use icons with transparent backgrounds , Match with background color .

if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.O) {
    builder.setSmallIcon(R.mipmap.launcher_icon);
} else {
    //  A picture with a transparent background , Match with background color 
    builder.setSmallIcon(R.mipmap.icon_notification)
            .setColor(Color.parseColor("#0972EE"));
}

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