"Paint" html table `td` elements on mobile web app - javascript

I'm working on a web application where the user needs to look at a grid of months and select whether documentation exists for a list of objects.
For the sake of user experience, I want to provide the ease of "painting" the grid. So say if the user knows the documentation exists for the whole year, she can just drag her finger across that row and every <td> in that row will have a class applied to it.
From what I can tell from Chrome Dev tools, I can get a lot of events firing when I attach a touchmove listener to each <td>, but the event's target is always the element the touch event started on and never on any other element.
Is there any way to have each <td> respond when a user drags his finger over a table?

Unfortunately the event target is set on the touchstart event so, as you drag your finger across the screen, the same event target is used as the origin of each touchmove event.
The only way around this I can think of would be to use the touchmove event to obtain the position of the touch and then figure out which table cell that would coincide with. If all your table cells are the same dimensions within a given table, taking the position obtained from the touchmove event and dividing it by the width and height of the table would give you the answer. Here's a quick snippet to get you started (this example assumes the table's position is at the very top left of the viewport):
var _columnWidth = 40;
var _rowHeight = 20;
var touchListener = function (e) {
var touch = e.touches[0];
var x = touch.pageX;
var y = touch.pageY;
var xIndex = Math.floor(_someTable.width / x / _columnWidth);
var yIndex = Math.floor(_someTable.height / y / _rowHeight);
};
_someTable.addEventListener('touchmove', touchListener, false);
So, if the width of the table is 80 and the height of the table is 100, and the x and y coordinates is 42 and 67 respectively, then xIndex would yield 1 and yIndex would yield 3 (meaning the second cell from the left and the forth cell from the top using zero-based indices).
Now this is a light example and won't magically solve your problem, but it's a good place to start. Hope this helps!

Related

Counting the number of times a user scrolled and moved his mouse using JS / Jquery

I'm trying to count the number of times a user scrolled the page (any direction) and moved his mouse using this jquery code:
$(window).bind('scroll',function(e){
scrolling++;
});
$(window).bind('mousemove',function(e){
mouse_moved++;
});
The problem with this is one scroll event or one mouse movement gives the variables 'scrolling' and 'mouse_moved' a very high amount instead of just incrementing it by one.
It seems whenever the scrubber / mouse position changed it is counting it as one event already, even though the original event isn't done yet.
How can I do this correctly? Count one scrolling and mouse movement event properly?
You need to track your state, e.g. detect when scrolling/moving starts, then again when it ends. And you need to decide what "ending" means — how long does the mouse have to be stationary again before you decide it's stopped moving? 5ms? 10? 15?
var scrolling = 0;
var scrollTimeout = 0;
$(window).bind('scroll',function(e){
cancelTimeout(scrollTimeout);
scrollTimeout = setTimeout(doneScrolling, 10); // 10 = 10ms
});
function doneScrolling() {
scrollTimeout = 0;
++scrolling;
}
...and similarly with the mouse move (with its own separate timer).

Fake scroll bars in browser

I want to provide the user with the experience of scrolling through content, but I would like to load the content dynamically so the content in their viewing area is what they would expect, but there is no data above or below what they are looking at. For performance reasons, I don't want that data loaded. So when they scroll down new data gets loaded into their view, and data previously in their view is discarded. Likewise when scrolling up. The scroll bar should represent their location within the entire content though, so using "infinite scrolling" or "lazy loading" does not look like what I need.
My solution may be that I need to re-architect things. As of now, my project is a hex-viewer that allows you to drop a binary file onto it. I create html elements for every byte. This causes performance issues when you end up with a 1MB file (1,000,000+ DOM elements). One solution would be to not use DOM elements/byte but I think this will make other features harder, so I'd like to just not display as many DOM elements at once.
Make a div, set overflow to scroll or auto. As user scrolls you can change the content of the div.
You could look at yahoo mail (the JavaScript based one) to see how they do it (they add rows with email as you scroll).
You don't necessarily need custom scroll bars.
You could look for some code here for custom scroll bars:
http://www.java2s.com/Code/JavaScript/GUI-Components/Scrolltextwithcustomscollbar.htm
or here:
http://www.dyn-web.com/code/scroll/
I'm looking for an answer to this question as well so I'll share where I'm at with it.
I have a large amount of content I want to display vertically and have the user scroll through it. I can load it all into the DOM and scroll normally but that initial creation phase is horribly slow and scrolling can awfully slow also. Also, I will dynamically add to it as I stream more data in.
So I want the same thing which is to be able to dynamically populate and update a non-scrolling area with content. I want to make it seem as if the user is scrolling through that content and have a model (which has lots of data) that is kept off the DOM until it would be seen.
I figure I'll use a queue concept for managing the visible DOM elements. I'd store queueHeadIndex and queueTailIndex to remember what off-DOM elements are shown in the DOM. When the user scrolls down, I'd work out what whether the head of queue falls off the screen and if it does update queueHeadIndex and remove it's DOM element. Secondly I'd then work out whether I need to update queueTailIndex and add a new element to the DOM. For the elements currently in the DOM I'd need to move them (not sure if they need animation here or not yet).
UPDATE:
I've found this which seems to have some promise http://jsfiddle.net/GdsEa/
My current thinking is that there are two parts to the problem.
Firstly, I think I want to disable scrolling and have some sort of virtual scrolling. I've just started looking at http://www.everyday3d.com/blog/index.php/2014/08/18/smooth-scrolling-with-virtualscroll/ for this. This would capture all the events and enable me to programmatically adjust what's currently visible etc. but the browser wouldn't actually be scrolling anything. This seems to provide mouse wheel driven scrolling.
Secondly, I think I need to display a scroll bar. I've had a look at http://codepen.io/chriscoyier/pen/gzBsA and I'm searching around more for something that looks more native. I just want it to visually display where the scroll is and allow the user to adjust the scroll position by dragging the scroller.
Stackoverflow is insisting I paste code so here is some code from that codepen link above
var elem = document.getElementById('scroll-area'),
track = elem.children[1],
thumb = track.children[0],
height = parseInt(elem.offsetHeight, 10),
cntHeight = parseInt(elem.children[0].offsetHeight, 10),
trcHeight = parseInt(track.offsetHeight, 10),
distance = cntHeight - height,
mean = 50, // For multiplier (go faster or slower)
current = 0;
elem.children[0].style.top = current + "px";
thumb.style.height = Math.round(trcHeight * height / cntHeight) + 'px';
var doScroll = function (e) {
// cross-browser wheel delta
e = window.event || e;
var delta = Math.max(-1, Math.min(1, (e.wheelDelta || -e.detail)));
// (1 = scroll-up, -1 = scroll-down)
if ((delta == -1 && current * mean >= -distance) || (delta == 1 && current * mean < 0)) {
current = current + delta;
}
// Move element up or down by updating the `top` value
elem.children[0].style.top = (current * mean) + 'px';
thumb.style.top = 0 - Math.round(trcHeight * (current * mean) / cntHeight) + 'px';
e.preventDefault();
};
if (elem.addEventListener) {
elem.addEventListener("mousewheel", doScroll, false);
elem.addEventListener("DOMMouseScroll", doScroll, false);
} else {
elem.attachEvent("onmousewheel", doScroll);
}
I imagine I'll have one class that listens to scroll events by either the virtual scroll method or the ui and then updates the ui scroller and the ui of the content I'm managing.
Anyway, I'll update this if I find anything more useful.
I think avoiding using DOM elements/byte is going to be the easier solution for me than creating a fake scrolling experience.
UPDATE: I ultimately solved this as explained here: Javascript "infinite" scrolling for finite content?
You're taking about using some serious javascript, specifically AJAX and JSON type elements. There is no easy answer to your questions. You'd need to do a lot of R&D on the subject.

Iscroll - Jquery - Get position on a list item

The error I'm having is the following:
To the right of my page, I have a list of interesting points (displayed on a map to the left of the page).
Because the list is so long, I am using iScroll 4 (great plugin).
However, what I would like to do is fire an event when the user has scrolled the list, so I can check which items are currently visible to the user. iScroll already has an event set up for that, so I have a function that fires when needed. However, I cannot seem to get the proper coordinates of my list items.
What happens is the following:
When the list loads, I get an .offset() value for the first element. offset.top = 35, because my list starts 35px lower than the top edge of the page. This is good.
When I scroll the list; say I pull it down for 500px; I would expect the new location to be 35px - 500px = -465px. However, it sill says 35. Scrolling though the list does not affect the elemen'ts coordinates even though it has moved.
How can I get the actual coordinates?
Playing with iScroll, I think I found the solution. the offset() function is javascript refering to the #scroller div, which doesn't change. However internally, iScroll uses its own x and y properties.
So you can refer to the iScroll offset like this
var myScroll = new iScroll(...)
alert(myScroll.y) // -- will return your offset (negative number)
add in iscroll.js
getScrollY: function () { var that = this; return that.y; },

How use JQuery/Javascript to scroll down a page when the cursor at the top or bottom edge of the screen?

Simple, I just would like to have it so when a user is dragging an item and they reach the very bottom or top of the viewport (10px or so), the page (about 3000px long) gently scrolls down or up, until they move their cursor (and thus the item being dragged) out of the region.
An item is an li tag which uses jquery to make the list items draggable. To be specific:
../jquery-ui-1.8.14.custom.min.js
http://code.jquery.com/jquery-1.6.2.min.js
I currently use window.scrollBy(x=0,y=3) to scroll the page and have the variables of:
e.pageY ... provides absolute Y-coordinates of cursor on page (not relative to screen)
$.scrollTop() ... provides offset from top of page (when scroll bar is all the way up, it is 0)
$.height()... provides the height of viewable area in the user's browser/viewport
body.offsetHeight ... height of the entire page
How can I achieve this and which event best accommodates this (currently its in mouseover)?
My ideas:
use a an if/else to check if it is in top region or bottom, scroll up if e.pageY is showing it is in the top, down if e.page& is in bottom, and then calling the $('li').mouseover() event to iterate through...
Use a do while loop... this has worked moderately well actually, but is hard to stop from scrolling to far. But I am not sure how to control the iterations....
My latest attempt:
('li').mouseover(function(e) {
totalHeight = document.body.offsetHeight;
cursor.y = e.pageY;
var papaWindow = window;
var $pxFromTop = $(papaWindow).scrollTop();
var $userScreenHeight = $(papaWindow).height();
var iterate = 0;
do {
papaWindow.scrollBy(0, 2);
iterate++;
console.log(cursor.y, $pxFromTop, $userScreenHeight);
}
while (iterate < 20);
});
Works pretty well now, user just needs to "jiggle" the mouse when dragging items sometimes to keep scrolling, but for scrolling just with mouse position its pretty solid. Here is what I finally ended up using:
$("li").mouseover(function(e) {
e = e || window.event; var cursor = { y: 0 }; cursor.y = e.pageY; //Cursor YPos
var papaWindow = parent.window;
var $pxFromTop = $(papaWindow).scrollTop();
var $userScreenHeight = $(papaWindow).height();
if (cursor.y > (($userScreenHeight + $pxFromTop) / 1.25)) {
if ($pxFromTop < ($userScreenHeight * 3.2)) {
papaWindow.scrollBy(0, ($userScreenHeight / 30));
}
}
else if (cursor.y < (($userScreenHeight + $pxFromTop) * .75)) {
papaWindow.scrollBy(0, -($userScreenHeight / 30));
}
}); //End mouseover()
This won't work as the event only fires while you're mouse is over the li.
('li').mouseover(function(e) { });
You need to be able to tell the position of the mouse relative to the viewport when an item is being dragged. When the users starts to drag an item attach an 'mousemove' event to the body and then in that check the mouse position and scroll when necessary.
$("body").on("mousemove", function(event) {
// Check mouse position - scroll if near bottom or top
});
Dont forget to remove your event when the user stops dragging.
$("body").off("mousemove", function(event) {
// Check mouse position - scroll if near bottom or top
});
This may not be exactly what you want, but it might help. It will auto-scroll when the mouse is over the 'border of the screen' (a user defined region). Say you have a 40px wide bar on the right of the screen, if the mouse reaches the first 1px, it will start scrolling. Each px you move into it, the speed will increase. It even has a nice easing animation.
http://www.smoothdivscroll.com/v1-2.htm
I get a weekly newsletter (email) from CodeProject, and it had some stuff that certainly looks like it will solve my problem... hopefully this can help others:
http://johnpolacek.github.com/scrollorama/ -- JQuery based and animates the scroll
https://github.com/IanLunn/jQuery-Parallax -- JQuery based, similar to above
http:// remysharp. com/2009/01/26/element-in-view-event-plugin/ -- JQuery, detects whether an element is currently in view of the user (super helpful for this issue!)
Also the site in #2 had some interesting code:
var windowHeight = $window.height();
var navHeight = $('#nav').height() / 2;
var windowCenter = (windowHeight / 2);
var newtop = windowCenter - navHeight;
//ToDo: Find a way to use these vars and my original ones to determine scroll regions

How can I react when a user touches an HTML element on an iPhone?

I'm displaying some HTML content in my iPhone app using a UIWebView. I have an image link, and I want it to change when the user touches it - at the moment the user puts a finger on the screen, rather than waiting until they lift their finger back off.
What CSS or JavaScript concept could accomplish this? I've looked at the hover and active states in CSS, but they don't seem to be what I'm after: hover relates to touch-up rather than touch-down, while active seems to have no effect at all.
You could try this.
I think it should be what you are looking for!
http://articles.sitepoint.com/article/iphone-development-12-tips/2
8: Touch Events
Of course, you use your iPhone with a
finger instead of a mouse; rather than
clicking, you tap. What’s more, you
can use several fingers to touch and
tap. On the iPhone, mouse events are
replaced by touch events. They are:
touchstart
touchend
touchmove
touchcancel (when the system cancels the touch)
When you subscribe to any of those
events, your event listener will
receive an event object. The event
object has some important properties,
such as:
touches — a collection of touch objects, one for each finger that
touches the screen. The touch objects
have, for example, pageX and pageY
properties containing the coordinates
of the touch within the page.
targetTouches — works like touches, but only registers touches on
a target element as opposed to the
whole page.
The next example is a simple
implementation of drag and drop. Let’s
put a box on a blank page and drag it
around. All you need to do is
subscribe to the touchmove event and
update the position of the box as the
finger moves around, like so:
window.addEventListener('load', function() {
var b = document.getElementById('box'),
xbox = b.offsetWidth / 2, // half the box width
ybox = b.offsetHeight / 2, // half the box height
bstyle = b.style; // cached access to the style object
b.addEventListener('touchmove', function(event) {
event.preventDefault(); // the default behaviour is scrolling
bstyle.left = event.targetTouches[0].pageX - xbox + 'px';
bstyle.top = event.targetTouches[0].pageY - ybox + 'px';
}, false);
}, false);
The touchmove event listener first cancels the default behavior of the finger move—otherwise Safari will scroll the page. The collection event.targetTouches contains a list of data for each finger currently on the target div element.
We only care about one finger, so we use event.targetTouches[0]. Then pageX gives us the X coordinate of the finger. From this value we subtract half the width of the div so that the finger stays in the center of the box.
Hope it helps!
Try the Javascript "onMouseDown", hopefully the mobile Safari will fire the event.
Link

Categories

Resources