Android平台提供了默认的通知栏实现，如下的代码就能实现：

NotificationManager manager = (NotificationManager) context.getSystemService(Context.NOTIFICATION_SERVICE);
NotificationCompat.Builder builder = new NotificationCompat.Builder(context);

builder.setContentTitle(getNotificationTitle())
       .setContentText(getNotificationContent())
       .setSmallIcon(iconDrawableId)
       .setTicker(getNotificationContent())
       .setAutoCancel(true)
       .setContentIntent(pendingIntent);

manager.notify(notifyTitleId, builder.build());

这种方式虽然简单，但图标不能为网络图片，因此我们需要使用自定义的方式。

刚开始想先显示通知栏，之后异步下载并图片并更新图标，但却一直不能显示网络图片，如下：

ImageRequest request = new ImageRequest(getNotificationStatusIcon(),
        new Response.Listener<Bitmap>(){

            @Override
            public void onResponse(Bitmap response) {
                remoteView.setImageViewBitmap(iconId, response);

            }
        }, 0, 0, Bitmap.Config.RGB_565,
        new Response.ErrorListener() {

            @Override
            public void onErrorResponse(VolleyError error) {

             }

        });

但图片获取成功了，显示无法成功。后来改变了顺序，先将图片下载了，之后再显示通知栏，居然显示正常了。

ImageRequest request = new ImageRequest(getNotificationStatusIcon(),
                           new Response.Listener<Bitmap>(){

                                @Override
                                public void onResponse(Bitmap response) {
                                    pushCustomNotification(context, response);

                                }
                            }, 0, 0, Bitmap.Config.RGB_565,
                            new Response.ErrorListener() {

                                @Override
                                public void onErrorResponse(VolleyError error) {
                                    pushDefaultNotification(context);

                                }

                            });
......

private void pushCustomNotification(Context context, Bitmap icon){
        Intent intent;
        try {
            intent = Intent.parseUri(getIntent(), 0);
            PendingIntent pendingIntent = PendingIntent.getActivity(context, 0, intent, PendingIntent.FLAG_UPDATE_CURRENT);

            final int notifyTitleId = ResourceUtil.getStringId(context,"push_mail_notification_title");
            NotificationManager manager = (NotificationManager) context.getSystemService(Context.NOTIFICATION_SERVICE);
            NotificationCompat.Builder builder = new NotificationCompat.Builder(context);
            final int iconDrawableId = ResourceUtil.getDrawableId(context, "mail_push_icon");
            final int iconId = ResourceUtil.getId(context, "push_notification_icon");

            final RemoteViews view = new RemoteViews(context.getPackageName(), ResourceUtil.getLayoutId(context, "layout_custom_notification"));
            view.setTextViewText(ResourceUtil.getId(context, "push_notification_title"), getNotificationTitle());
            view.setTextViewText(ResourceUtil.getId(context, "push_notification_content"), getNotificationContent());
            view.setImageViewBitmap(iconId, icon);


            builder.setCustomContentView(view)
                    .setSmallIcon(iconDrawableId)
                    .setTicker(getNotificationContent())
                    .setAutoCancel(true)
                    .setContentIntent(pendingIntent);

            manager.notify(notifyTitleId+1, builder.build());


        } catch (URISyntaxException e) {
            e.printStackTrace();
        }

    }