Category Archives: Personal Diaries

Multi-device Syncing Strategy

While reconstructing my app (WordsBaking), a big challenge is data synchronizing. I’ve spent a lot of time thinking about possible ways, and still not sure if I got the best one.

There are two main problems I am facing.

Physical timestamps can’t be trusted

When the user is online, well we may actually calculate the timestamp based on the difference between client and server that can be somehow trusted at some degree. However the process could be really complex if we want to get every detail right. And if the user is offline, you can never tell the timestamp that can be trusted.

So I have to get rid of it, and choose only to trust the physical timestamps with limited correction (lower and upper bounds).

There are too many records to compare when syncing

For my app, there could be thousands of records. And I can’t just upload all of them every time to check whether their timestamps are smaller than the copies on the server. Another independent timestamp for syncing has to be set for quickly picking up records that might have newer version.

The solution seems to be really obvious, just add another timestamp for sync seeking. The question keeps around in my mind is, do both of the timestamp for seeking and for version comparing necessary?

If they are, the complete synchronizing logic would be:

Client

clientStamp: updated every time after syncing, and the value equals the server time when that syncing happens.
itemUpdateStamp: updated every time when an item gets created/updated/removed, and the value should be greater than the latest clientStamp.

When syncing, client would upload the clientStamp and changed items along with their own itemUpdateStamps. And then it would receive changed items from the server along with the new clientStamp, it won’t receive new itemUpdateStamps because it’s not the device that would compare the records version.

Server

For every record in the database, it will have both the clientStamp and the itemUpdateStamp. When receiving a syncing request, it will first find all the records that have the clientStamp greater than the value it receives or have the same ids, and then comparing itemUpdateStamp with the items it receives respectively if they match the items it receives. If a change from the client has a newer itemUpdateStamp, then update the record in database (with the upper bound of itemUpdateStamp being the current time of the server). Otherwise, send the change to the client.

Seems to be quick clear after writing the logic down. ;)

Later I added another feature called passive syncing, thus the client is now able to sync down some related data on demand.

Original link of this archive: http://vilic.info/blog/archives/1159
本文的原始链接: http://vilic.info/blog/archives/1159

iOS Web Application Directly Using Online URI

Will Apple App Store approve web apps that directly using online URL and resources?

Yes.

When I submitted my app to Apple App Store, I was worrying about a rule that forbidding downloading code in any way or form. And as a web app that downloads its main code only after installation, it does seem to violate this rule. But luckily, it’s finally approved.

Apple App Store http://itunes.apple.com/app/id843170841
See also the Windows Phone version http://www.windowsphone.com/s?appid=a3e70b25-b048-4bef-996f-cc2b30a6eda2

And congrats to myself that WordsBaking is scheduled to be FEATURED in Windows Phone Store (China) tomorrow. ;)

Original link of this archive: http://vilic.info/blog/archives/1109
本文的原始链接: http://vilic.info/blog/archives/1109

An Underestimated Tool in Windows: HTA (HTML Application)

I can’t find a convinced source telling in which specific date did HTA become available, but it seems to be earlier than the year 2000.

On the official introduction page of HTA, there’s a highlight saying “The Power of Trust”. Unlike normal HTML pages running in a normal browser, HTA can have almost the same permissions that an exe file could have. Which gives it access to varieties of ActiveX that are not available in normal browsers due to security reasons.

I am always wondering why only a few people know and use HTA? Hmm, maybe one of the reasons is its “Microsoft” tag. I have given up the thoughts hoping HTA could be relatively mainstream, however, for developers who use JavaScript and HTML, HTA could still be a good choice to write some lite productive tools for your colleagues and yourself.

NodeJS would certainly have much better ecosystem now but for some specific tasks I still prefer tools with GUI… T-T (Now I also use NodeJS to do some batch work.)

But it was a shame that Microsoft stopped making it better. Wishes.

Original link of this archive: http://vilic.info/blog/archives/1097
本文的原始链接: http://vilic.info/blog/archives/1097

Let’s Again Talk About IE (Internet Explorer)

As an amateur but the same time professional front-end engineer, one of the most common things in my life is to press F5 in different browsers.

When this word was not “standardized” as it is now, I was used to pressing that button in several versions of IE, Chrome, Firefox, Safari, and, if I was in a really great mood, Opera. So I hadn’t suffer less than anyone. Especially from IE 6/7.

Now I basically test only in IE 8+ and Chrome. If the project is platform targeted, even better. There has been a lot of scoffs about IE  on compatibility and performance these years, which make me sort of sorry. People would always be fond of the new and tired of the old, even though it is the old one which brings the bright start to all these wonderful things.

IE 6 in my opinion is a great browser. It is out of date but It was well-designed and ignited many features in modern browsers. Actually, tons of newly added features in HTML5 or CSS3 can be imitated in IE 6, a browser which was released 12 years ago. And many earlier IE-only features have become the standards.

The earlier versions of IE is buggy and perform slow, but they perfectly served the days when it was released.

Well I am not trying to ask people not to give it up, but just hoping we can keep the respect, which this browser deserves, to it in its last days.

Microsoft seems to have realized their mistakes on detaining the developing of IE these years and brings us the new IE 9/10/11. Compatibility issues have become minor since version 9 (also it brings us fully GPU acceleration, which is a really important event for web apps), and since version 10, IE finally caught up the steps of modern browsers.

IE now is almost ready for web apps which could be as great as native apps, and I am looking forward to the booming of mobile web apps in the next several years. :)

Original link of this archive: http://vilic.info/blog/archives/1080
本文的原始链接: http://vilic.info/blog/archives/1080

Thoughts after Developing WordsBaking

Several months ago I started my own project called WordsBaking, which is a tool developed for helping students or learners like me to remember new English words. Considering the time and resources I have, I finally decided to use HTML/CCS/JS technologies so that it could be easier to have the versions for the three major mobile platforms.

But there would certainly be some subsequent issues. In last post, I wrote something about performance, gestures and preventing tap highlight. And in this post, I am gonna write some notes about browser bugs.

First of all, I like IE 10 Mobile quite much, comparing to original Android browser. But unfortunately, it still gets some weird bugs.

1. Scrolling issue with CSS3 transform.

I spent a lot of time locating this issue, as scrolling should be one of the most basic features, which in other word should be stable enough. It is a list of which the parent node has the style “overflow” with value “auto”. And the pseudo element “:active” of the list items has a transform with transition: translateX, so that when finger is on the item, it moves a little bit rightwards. Then the problem came, you can’t scroll the list down directly. If you want to do so, you’ll have to scroll up a little first. And, after you scroll to the bottom, you can even continue scrolling up (though the scrolling becomes no longer smooth).

So I have to change the transform to some older ways, like margin, padding, etc.

2. Scrolling issue with phone:WebBrowser control.

Ohh, again scrolling. To use pointer series of events built in IE, I have set -ms-touch-action to none under html selector. So that the page won’t move around or dance with your fingers. It works well until you get some elements with style “overflow: auto;” (or “scroll” I guess). After a list is scrolled to the top or bottom, if you put away and back your finger and continue scrolling, the whole page starts a bouncing effect. Luckily, this only happens in a phone:WebBrowser control. But unfortunately, I am using that control to wrap up my app.

I guess there should be a solution but I really haven’t found it.

Okay, so these are issues with the front end. On back end, I chose NodeJS as I am more confident with my JS skill. But it really took me quite a lot time to start due to the poor documentation. I am not familiar with back end and everyone knows I write front end all the time. I can’t say it would be a challenge to write the back-end stuffs I’ve done these days, but it was a great chance to learn new things.

The main problem I have is lack of database related experience, I don’t know how the db engine works in the box, so I don’t know how would my structures and logic perform. T-T

But back to NodeJS, I am quite missing my VEJIS, which helps JSers coding without looking for online documentations. Oh dear you know how it feels when you press the “.” but there is no accurate auto completion and hints? It might not be that helpful after one is extremely familiar with a framework, but before that, it helps a lot. And one more thing, we are never be that familiar with every new code line we write…

A thousand words are reserved here…

wb

So, I am very excited as WordsBaking for WP is almost ready for beta, after months. I always believe the power of a team, but when a team is not available, I also believe my own skills. Thanks my CTO (Chief Track Officer) for Tracking my developing progress btw, or I wouldn’t be able to finish the beta version. :)

Original link of this archive: http://vilic.info/blog/archives/1071
本文的原始链接: http://vilic.info/blog/archives/1071