使用 Picasso 库设置自定义通知图标

    PendingIntent pendingIntent = PendingIntent.getActivity(context,
    uniqueIntentId, intent, PendingIntent.FLAG_CANCEL_CURRENT);

    final RemoteViews remoteViews = new RemoteViews(context.getPackageName(), R.layout.remote_view_notification);
    remoteViews.setImageViewResource(R.id.remoteview_notification_icon, R.mipmap.ic_navigation_favorites);

    Uri defaultSoundUri = RingtoneManager.getDefaultUri(RingtoneManager.TYPE_NOTIFICATION);
    NotificationCompat.Builder notificationBuilder =
            new NotificationCompat.Builder(context)
                    .setSmallIcon(R.mipmap.ic_navigation_favorites) //just dummy icon
                    .setContent(remoteViews) // here we apply our view
                    .setAutoCancel(true)
                    .setContentIntent(pendingIntent)
                    .setPriority(NotificationCompat.PRIORITY_DEFAULT);

    final Notification notification = notificationBuilder.build();

    if (android.os.Build.VERSION.SDK_INT >= 16) {
        notification.bigContentView = remoteViews;
    }

    NotificationManager notificationManager =
            (NotificationManager) context.getSystemService(Context.NOTIFICATION_SERVICE);

    notificationManager.notify(uniqueIntentId, notification);

    //don't forget to include picasso to your build.gradle file.
    Picasso.with(context)
            .load(avatar)
            .into(remoteViews, R.id.remoteview_notification_icon, uniqueIntentId, notification);

然后在 layouts 文件夹中定义布局：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="@android:color/white"
    android:orientation="vertical">

    <ImageView
        android:id="@+id/remoteview_notification_icon"
        android:layout_width="60dp"
        android:layout_height="60dp"
        android:layout_marginRight="2dp"
        android:layout_weight="0"
        android:scaleType="centerCrop"/>
</LinearLayout>