Sunday, March 8, 2015

Just few random notes on Parse and Mobile FileUpload

FileUpload on mobile

 <input type="file" accept="image/*">
Android (Chrome and 4.4 native) provides a reasonable, but not-pretty, interface.

If you want to use camera, add the capture camera option. Note that it will not allow other images. allows to upload the file and query it by URL. It`s very simple, but note that it means an image access counts as an API call, and as images usually come in packs, this can cost your quota.

Detect change on textarea

Use $('#textAreaId#).on('change',function() { do something here });
change will be called when the focus is changed and any of the inside-text change.

Parse model update

On many views, you will want to first refresh the view from a saved DB element, and then on edit update(re-save) the element and refresh the view again.
For this pattern, always keep a cached parse object which was returned from the DB and is connected to parse via the row-id.
On refresh, update the cached-element, if found in the DB.
On edit either re-save (on the cached one) if it already exists, or save a new one and create cache.

You can save multiple objects via Parse.Object.saveAll (array)

Parse queries
When querying a pointer, sadly, you can't just pass an instance of a previously returned item (item itself != item pointer). You have to create a pointer object. 
var pointerToUser = {  __type: "Pointer",  className: "_User",       objectId: };

You can combine multiple queries using Query.or(q1, q2)

Parse weird save/query results

  • Parse will not fail if you query a db class which do not exist at all. Beware of Parse.Object.extend("SpellingMistakeWillNotBeNoticed");
  • It will also allow you to save db columns which do not exist at all. Beware of (item.set('spellingMistake',666).

Tuesday, February 3, 2015

Tinder-clone in javascript

Tinder-like moving images:

Have a look at the end result here.
And now let`s go step by step:

[Step 1]
  • Check if it actually doing anything: Use requeststAnimationFrame (+big function to make it better)
  • The actual moving of the element is done in js using: = 'translate3d('+newX+'px,'+ newY+'px,5px)';
  • To return it to first position, add style{transition:all 0.3s;}
  • To make sure the image is not dragged by itself:   user-drag: none;  -moz-user-select: none;  -webkit-user-drag: none;
[Step 2]
Lets use a card-style (see here) and move the entire card.

[Step 3]
Add tinder buttons  (V,X) below, add z-index to the .card ( z-index:1;    position: relative; ) so that it will move above them.
Also note that when we move the card down, it causes scrolling (solve by adding overflow:hidden to the main content) , and that the end of the content ends with the end of the buttons instead to extend to the full view. This is solved by a small js, to change main content size according to full size- header height.
Last change is addition of rotation to the transform  rotate( startX-newX)*0.05 + deg

[Step 4]
check the release location on hammer "panend" event, and a check of ev.isFinal and ev.deltaX ev.deltaY.  If it is above a threshold, move it far away.
Also , let`s use multiple cards, so we will use multiple Hammer instances, one for each card. Luckily hammer supports it and hammer events are separated per card.

[Final notes]
On mobile, panning may cause scrolling the window down. To avoid this, add:
        $(document).bind('touchmove', function(e) {

Saturday, December 6, 2014

Searching for close matches to my choices


Every user is asked a serious of binary questions:
What do you prefer, cats or dogs
Do prefer winter or summer
Do you consider computer-science gradatees as scientinst. Yes/No

There will be lots of users (1M), but not more than 300 questions.
Find the 10 closest matches for a certain user.


This problem is a similar to search nearest-neighbors of  Hamming distance. It is simplified as there are only binary(yes/no questions), hamming works with more options, but nearest-neighbors is extremely difficult problem....

1. For a query for unkown, new user, this stackoverflow question says that it`s a tricky problem.  For short distances (4 from 32 bit integers) BK-tree and VP-tree can speed up queries up to 10 times, or even 1000 times for very short distance of 1.   For medium ranges and above, no good data structure exists, and brute-force is needed.

If we can assume that our users always have 10 close matches with short distance, we can use one of the suggested data-structure, otherwise, just use blunt-force each time.

2. For a big calculation of all the matches, there might be a better solution. Didn`t find one.

Tuesday, November 4, 2014

Page pagination in JqueryMobile


  Infinite number of different, similar, pages like Tinder app, where each page contains images,labels and text.
One ajax request to the server contains the data for the next 10 pages, so we won`t do the "simple" solution of reading a new ajax page each time.


We will have 3 pages  (match1, match2, match3) each one as a "next" button pointing to the next one.
We will save the data of the next 10 pages at any given point, let`s call it the model.
On each page pagebeforeshow event, we will change the data on the non visible page.
Once the model data is empty (all the 10 pages were seen), we will use an ajax call to fill the model.

model state= 50,51,52,53,...,59
[page1] [page2] [page3]

on the first time (when all pages are empty) and later, when one page becomes obsolete, we will fill the obsolete pages
  50            51         52
[page1] [page2] [page3]

  53            51         52
[page1] [page2] [page3]


 59            57         58
[page1] [page2] [page3]

when we get to this state, once 58 becomes active, we will want to replace page2 with 60, so we will do an ajax call and update the model with it,
delicate points:  
  • If ajax call is on it`s way, there is no reason to make a new call.
  • We should also clean the previous page to null data (default image and text), in case the user will be faster than our ajax call. We may even consider creating a "loading" progress bar, if the ajax is very slow.


Thursday, September 11, 2014

Facebook user authentication

On the client side, you can call the facebook api to login a user using their popup window. The user will get an very temporary (few hours) access-token which will be saved in a cookie (by the facebook api automatically) and can be used to create API calls.

In this post, we will discuss user-authentication which not quite the same. We want that our server will know that the user is legit.

How it worked before:

Signup: You had the signup with user&password pair (and usually an email for lost password...). The server will save this pair in the database.
Sign-in: Each time you attemp to login, you send the pair to the server and the server replay with good or bad.
Sign-in cookie: As you don`t want the user to re-login in every page, or every day, you can decide to put a cookie which bypass this. An (unscure) cookie can be the user&password, but in this case, if someone browse the cookies on the user-machine, he can see them. It can also be a temporary access-token, for example a unique number which is good for one-day and saved with the user/password pair. Tomorrow, it will be deleted and the user will have to relogin.


Signup: The user already signed-up for facebook years ago. The user will have to permit your application to see his details, on the first login.
: The user will see facebook login.
Sign-in cookie: facebook, behind-the-scenes, saves a temporary access-token so you will not have to, so if you call the user login again after a short time, the user will not see the login dialog.

The user code for using it is quite short, as facebook sdk is doing most of the work, and can be seen at facebook api login samples.

Combine the two: But how can my server know that the user is a legit one?

On the client side, if login was correct, we can send the server the facebook user-id and use it as a token.  This is only half-secure, as anyone with some programming skills, can get the facebook user id and modify our client code to impersonate someone else.
But, it will stop non-programmers/hackers , and can be used for prototyping ONLY stage.

A proper authentication is to send the server the facebook-id and the access-token (which is like user/password pair). The server will ask facebook to verify it (instead of looking into the local database) and then send a temporary cookie, which is the same as the user/password cookie. This will used so the user will not have to login again and again, and that our server will not have to verify the facebook-id/access-token.

And to the implementation

  1. Do it yourself means server code for asking facebook verification and a db table with facebook-user-id to session.
  2. On node.js you can use passport library to do part of the work for you.
  3. Using facebook parse clould-server framework, they will do all of it, including storing the db for you (but it is limiting as you won't have direct access)

Tuesday, September 9, 2014

PhoneGap build

Phonegap build is a great tool for quick testing of your mobile-app as a deployed app. Copy all the relevant client file locally  (including /js /img /css folders). Make sure you have index.html file. create a simple config.xml file.

<?xml version="1.0" encoding="UTF-8"?>
<widget xmlns=""  xmlns:gap="" id=""  versionCode="10" version="1.1.0">
  <!-- versionCode is optional and Android only -->
    MyName application
  <author href="http:/" email="">
    Developer name


Facebook login depends on a domain which you configure at facebook. If your local app is deployed on the phone and the page is not served from the server, it will fail to work.

TODO: solution: load your facebook-login page from the server.

beauty:  to have integration with facebook native app, you will need to work harder and use a plugin, lets ignore for now.

JQueryMobile performance

JQueryMobile defaults are extraordinarily bad and causing bad performance. But with few tweaks you can get to an almost-native performance, as long as you are ok with reduced visual beautiy.

See this blog for some ideas/details/hacks.

Bad transitions performance on Android

On Android, on page-change there is a bad effect of "jitter" once before moving to the page. It is not seen of chrome pc.
few approaches (see stackoverflow)
1 .Simplest : change transition to none.  Fastest on Android. data-transition="none". It also make the wierd temporary scroll bar go away
$.mobile.defaultPageTransition  = 'none';
$.mobile.defaultDialogTransition = 'none';
$.mobile.buttonMarkup.hoverDelay = 0;
Note some places say u need user-scalalbe=no on phono gap even with none data-transition

2. using this: <meta name="viewport" content="width=device-width, user-scalable=no" /> fade works fine without flicker, but it is still slow.

Slider/Range widgets are very slow on Android

known issue planned to be solved on 1.5
iOS performance was ok, on the one sample iPhone I tried.

Click delay?

1. One common internet opinition is to use . Didn`t help me much... 2.   On JQueryMobile I believe there is another issue. When you click on a button, the blue highlight starts, and the actual action/page-transition occurs considrable time afterwards (half-a-second...) You can remove this, by adding the fastclick class to relevant elements, and declare it as below, but note that it can cause problems with paenl buttons and that the highlight disappears...
$( document ).one( "pageshow", function() {
               return false;

TODO; an actual better solution will be to first trigger an async-action (like page change), then show the blue-highlight. It appears it work the other way around now.
wierdly checkbox widget work better.

How to choose multi-panel or single?:

Approach 1 -  copy the header,panel each time.

It is better to have two separate pages (.html), one which each page in it.

<div data-role="page" id="profile">

    <div data-role="header" data-position="fixed" data-tap-toggle="false" data-id="persist1" data-theme="a">
      <span class="ui-title">Edit Profile</span>
        <div class="ui-btn-right">
            <a id="myButton1" class="headerButton" href="index.html" data-role="button">profile</a>            <a id="myButton2" class="headerButton" href="index2.html" data-role="button">index2</a>

        <a href="#myPanel" class="ui-btn ui-btn-left ui-icon-bars ui-btn-icon-notext">not-visible</a>

   <div data-role="panel" id="myPanel">
        <h2>Panel Header</h2>
      <div data-role="main" class="ui-content" id="main-profile">
         profile page

</div> <!--of page-->

in this case, there are three issues:
1. Ugly code which is the same for each page.
2. On transition, the header slightly change, unless you add it data-theme='a' (the default is bad)
3. If you are using multiple pages in the same .html file, after you move to another page, the panel fails to work, probably as we have multiple panels with the same-id.

Approach 2 -  external header and panel

In this case, you have to add a script above ,otherwise the external panel/header will not shown at all.

  $( document ).on( "pagecreate", function() {
  $( "body > [data-role='panel']" ).panel();
  $( "body > [data-role='panel'] [data-role='listview']" ).listview();

  $( document ).one( "pageshow", function() {
   $( "body > [data-role='header']" ).toolbar();
   $( "body > [data-role='header'] [data-role='navbar']" ).navbar();




<div data-role="header" data-id="my-header" data-position="fixed" data-tap-toggle="false" data-theme="b">
     <a href="#myPanel" class="ui-btn ui-btn-left ui-icon-bars ui-btn-icon-notext">not-visible</a>
    <div class="ui-btn-right">
            <a id="myButton1" class="headerButton" href="#first" data-prefetch="true" data-transition="fade" data-role="button">profile</a>
            <a id="myButton2" class="headerButton" href="#second" data-prefetch="true" data-transition="fade" data-role="button">home</a>
</div><!-- /header -->

<div data-role="panel" id="myPanel">
        <h2>Panel Header</h2>
        <p>You can close the panel by clicking outside the panel, pressing the Esc key or by swiping.</p>

<div data-role="page" id="first">
    <div data-role="content"> 
        <p>The content</p>     
        <p>View internal page called <a href="#second">second</a></p> 
    </div><!-- /content -->

<div data-role="page" id="second">
    <div data-role="content"> 
        <p>I'm the second content 2nd</p>     
        <p><a href="#first">Back to first</a></p> 
    </div><!-- /content -->


Issues with this approach
1. You will have to change pragmatically the title, active-button of the header once you move to another page
2. still need the data-theme="a" to have any theme to your page.

Let`s discuss the events in this scenario.  If you programtically modify the content of the page and not loading a different page, the beforecreate,create and init event will be called the first time you move to that page, but not afterwards.  Also remember you have to manually call the page enhance, if your change require widget change.
(Navigate from A to B)
page B---pagebeforecreate   (ONCE)
page B---pagecreate            (ONCE)
page B---pageinit                 (ONCE)
page A---pagebeforehide
page B---pagebeforeshow
page A---pageremove
page A---pagehide
page B---pageshow 

            activepage =  $.mobile.pageContainer.pagecontainer("getActivePage");

            console.log( activepage[0].id);
You can put it on the pagebeforeshow event , as example.


For Android -like drawer:
 <div data-role="panel" id="myPanel"  data-display="overlay" data-position-fixed="true" data-theme="a">
data-position-fixed="true"  - you content will always jump up when you open.
data-display="overlay"  for Android style, use "push"/"reveal" for iOS style.