I might be missing something, but it seems that Meteor's "magic" revolves around binding data to DOM elements, and updating text and HTML fragments via handlebars: http://docs.meteor.com/#reactivity
This is great, however, when trying to write a meteor app that displays live data in a <canvas> element, I cannot figure out the "meteor way" to update my canvas when the live data changes, since the canvas is populated via JS code like:
var g = canvas.getContext('2d')
g.fillRect(x, y, w, h)
and not data-backed text in the HTML template.
I am trying to draw on the canvas using data from a Meteor.Collection.
My only thought was to embed canvas-drawing JS code in the HTML template in a script tag populated by handlebar vars, but this seems wrong since meteor's events and data-binding code is already client-side JS.
Is there some way listen for live data changes, which triggers drawing on the canvas via JS instead of HTML elements/text?
Please let me know if I can clarify the question in some way
Update:
Tom's answer below made me notice Meteor.deps, which look to allow executing arbitrary code in a reactive context:
http://docs.meteor.com/#on_invalidate
I will try this out and update here if it works.
Perhaps the answer to your question is to use Collection.observe (http://docs.meteor.com/#observe) and trigger the relevant redrawing code in the various callbacks.
For instance, something like:
Rectangles.observe({
added: function(rect) {
var g = canvas.getContext('2d');
g.fillRect(rect.x, rect.y, rect.w, rect.h);
},
// etc
})
This works:
var Shapes = new Meteor.Collection('shapes')
if (Meteor.is_client) {
// Function that redraws the entire canvas from shapes in Meteor.Collection
function drawShapes() {
var shapes = Shapes.find({})
shapes.forEach(function(shape) {
// draw each on canvas
})
}
var startUpdateListener = function() {
// Function called each time 'Shapes' is updated.
var redrawCanvas = function() {
var context = new Meteor.deps.Context()
context.on_invalidate(redrawCanvas) // Ensures this is recalled for each update
context.run(function() {
drawShapes()
})
}
redrawCanvas()
}
Meteor.startup(function() {
startUpdateListener()
})
}
I had some trouble with updating the canvas so I created this simple game demo:
https://github.com/randompast/Meteor-SimpleGame
Related
I've got a non-angular page made with fairly basic JS, and thought it'd be a splendid idea to try and add learn some Angular2 and use it for some new functionality.
My plan was that I'd bind an Angular2 component to an object that is being updated by the old code, and I'd use Angular2 magic to update a chunk of UI.
The problem is I cant convince Angular2 to react to any changes made in the outside JS. What the trick to doing that? Attempts at googling the problem lead to in depth explanations of Angular2's change detection process, which hasn't been helpful so far. Is this just an awful idea?
I found a random Angular2 jsfiddle and hacked it up to show the problem. Strings are added to 'window.names', but you dont see them until one is added from the angular side: https://jsfiddle.net/byfo3jg3/ . The code follows:
var names = ['Joe'];
setTimeout(function() {
names.push("Frank");
}, 1000);
setTimeout(function() {
names.push("Sterve");
}, 2000);
setTimeout(function() {
names.push("Garfield");
}, 3000);
(function() {
var HelloApp,
ListThing;
ListThing = ng
.Component({
selector: 'list-thing',
template: '<ul><li *ng-for="#name of names">{{name}}</li></ul>',
directives: [ng.NgFor]
})
.Class({
constructor: function() {
this.names = window.names;
setTimeout(function() {
this.names.push("Oh hai");
}.bind(this), 10000);
}
});
HelloApp = ng
.Component({
selector: 'hello-app',
template: '<list-thing></list-thing>',
directives: [ListThing]
})
.Class({
constructor: function() {}
});
document.addEventListener('DOMContentLoaded', function() {
ng.bootstrap(HelloApp);
});
}());
You will need to set the NgZone to window object and then call run function of the zone.
Please refer to Angular 2 How to get Angular to detect changes made outside Angular? SO Question
names should be component property to work inside of template:
constructor(){this.names = window.names}
Changes to window.names will not be detected by angular, so you have few options: poll names using setInterval(()=>{this.names = window.names}, 1000) or expose global callback:
constructor(zone:NgZone)
{
window.notify = ()=> {
zone.run(()=> {
this.names = window.names;
});
}
}
and call it from plain js window.notify() or use other methods to invoke change detection.
Is this just an awful idea?
Yes.
Angular's automatic change detection system assumes that changes to data (that you want your components to display) are happening inside an event handler that is monkey-patched by Zone.js. Because then Angular's change detection will execute when such an event handler fires (well, technically, it will execute after the event handler finishes).
If you want a component view to automatically update, you have to change the bound data inside Angular – inside the Angular zone. As #Jigar answered, you can modify your code to call angularZone.run(_ => // make changes here), but if you have to do that, you might as well move the code that manages and manipulates the data into a service (or a component, if the logic is minimal).
See also Günter's alternative approach: set up an event listener inside Angular (hence inside the Angular zone). Then fire that event whenever you make changes outside the Angular zone.
I am currently using iron-router and this is my very first attempt to try out the Meteor platform. I has been running into issues where most of the jquery libraries failed to initialized properly because the of the way Meteor renders html, $(document).ready() fires before any templates are rendered. I am wondering is there any callbacks from Meteor/iron-router that allows me to replace the jQuery's dom ready?
Also, how should I (easily and properly) handle the live update of the dom elements if some of them are customized by jQuery/javascript?
This is what i am currently doing, i feel like it is very hackish and probably would run into issues if the elements got updated after the initialization.
var jsInitalized = false;
Router.map(function () {
this.route('', {
path: '/',
layoutTemplate: 'default',
after: function(){
if(!jsInitalized){
setTimeout(function(){
$(document).ready( function() { $$$(); });
}, 0);
jsInitalized = true;
}
}
});
}
With Meteor you generally want to think about when a template is ready, not when the dom is ready.
For example, let's say you want to use the jQuery DataTables plugin to add sorting to a table element that's created by a template. You would listen to the template's rendered event and bind the plugin to the dom:
HTML:
<template name="data_table">
<table class="table table-striped" id="tblData">
</table>
</template>
JavaScript:
Template.data_table.rendered = function () {
$('#tblData').dataTable();
};
Now anytime the template is re-rendered (for example, if the data changes), your handler will be called and you can bind the jQuery plugin to the dom again.
This is the general approach. For a complete example (that includes populating the table with rows) see this answer.
Try making a separate .js file, call it rendered.js if you'd like. and then;
Template.layout.rendered = function ()
{
$(document).ready(function(){console.log('ready')});
}
I use template layout, but you can do Template.default.rendered. I hope that helps.
Also take a look at this part of documentation, especially the Template.events; http://docs.meteor.com/#templates_api
I use Meteor v0.8.0 with Iron Router (under Windows 7) and here is how I handle 'DOM ready':
When I want to modify the DOM after a specific template has been rendered:
I use Template.myTemplateName.rendered on the client side :
Template.blog.rendered = function()
{
$('#addPost').click(function()
{
...
});
}
When I want to modify the DOM after any new path has been rendered:
I use Router.onAfterAction, but there seems to be a trick:
Router.onAfterAction(function()
{
setTimeout(function()
{
$('.clickable').click(function()
{
...
});
}, 0);
});
Notice the setTimeout(..., 0), it doesn't work for me otherwise (DOM empty).
Notice that you can use onAfterAction on specific path, but most of the time I think it is redundant with the Template.myTemplateName.rendered method above.
What seems to be missing:
A way to modify the DOM after any template has been rendered.
According to the Meteor documentation, a callback assigned to Template.template_name.rendered will execute after each instance of template_name has finished rendering. I have been trying to use this feature to attach jQuery plugins (such as TagsManager or DotDotDot) to DOM elements generated by the templates. The "natural" way to do this would be something like:
Template.template_name.rendered = function () {
var template = this;
var elem = $('input#tags'+template.data._id);
elem.tagsManager(); // doesn't work
}
However, this does not work -- the expected behaviors do not come out attached to the element. The jQuery selector works properly and, by logging the internals of tagsManager(), I can see that the event handlers do seem to get attached, but after .tagsManager() finishes up, they are somehow unattached.
The "usual" solutions of wrapping the code in a $(document).ready or a short setTimeout suffer from the exact same behavior:
Template.template_name.rendered = function () {
var template = this;
$(document).ready(function () {
window.setTimeout(function () {
var elem = $('input#tags'+template.data._id);
elem.tagsManager();
}, 100); // 0.1 seconds + $(document).ready doesn't work
});
}
I only got it to work by giving an unrealistically high setTimeout time, such as 3 seconds:
Template.song.rendered = function () {
var template = this;
console.log("Template for "+template.data.title+" created");
$(document).ready(function () {
window.setTimeout(function () {
var elem = $('input#tags'+template.data._id);
elem.tagsManager();
}, 3000); // 3 seconds + $(document).ready works
});
}
As a matter of fact, even replacing elem.tagsManager() by a simple elem.on('click',...) suffers from the same behaviors as described above -- which is why the guys at Meteor have given us Template.template_name.events, I guess. However, this kind of breaks all interesting plugins, and forces us to rely on hacky, dangerous code such as the above. Is there a better way?
In the template, wrap the div you want to apply the jQuery with {{#constant}} helper. This will kill all reactivity you may have on elements wrapped up.
If you need reactivity or constant did not help, try this hack. I unbind the event of the element when rendered is called and bind it right after. The problem in this case is that rendered is called like a dozen times and it screw up some way I haven't figured out. Try debugging it to see how many it is called with console.log in the first line of rendered.
Hope it helps!
check that package : https://github.com/Rebolon/meteor-animation/blob/master/meteor-animation-client.js
line 38 to 56
it uses template.rendered with a cursor observer.
It might help you coz it also uses jquery.
I am trying to create a group of draggable DOM objects using jQuery UI's .draggable() that are populated through Meteor subscriptions. The code I came up with looks like
Meteor.subscribe('those_absent', function() {
$( "li.ui-draggable" ).draggable( { revert: "invalid" } );
});
Meteor.subscribe('those_present', function() {
$( "li.ui-draggable" ).draggable( { revert: "invalid" } );
});
These correspond with some Meteor.publish() calls, so that any time the collection changes, the .draggable() behaviour will be attached. At least, that was my intention.
However, it only works once - once one of these <li>'s has been dragged and dropped, then they are no longer draggable at all.
When the objects are dropped, I'm firing a custom event that is attached to the Template for the item like so
$( "#c_absent .inner-drop" ).droppable({
drop: function( event, ui ) {
ui.draggable.trigger('inout.leave');
}
});
Template.loftie_detail.events = {
'inout.leave': function (e) {
Lofties.update({_id:this._id}, {$set: {present: 'N' }});
}
};
So, my thinking is that this change to the collection on drop should propagate through the pub/sub process and re-run the .draggable() line above. But it doesn't seem to.
The complete code for this can be seen here https://github.com/sbeam/in-out/blob/master/client/inout.js and the app is live at http://inout.meteor.com/ (there are some other probably unrelated issues with items randomly losing values or disappearing from the UI altogether)
So if my understanding of how pub/sub works in Meteor is off, it would be good to know. Or is there a more efficient way to achieve this UI behavior binding that works without it?
The way I have implemented this in my apps is with the method shown by #lashleigh.
I have a template event that listens using code like this :
Template.myDraggableItem.events({
'mouseover .workItem' : function() {
$(this._id).draggable();
}
});
Then I listen for the dragstop like this.
$('body').on('dragstop', '.myDraggableItem', function (e) {
// Update the collection with the new position
};
You can see the app that's using this code at aduno.meteor.com
I am a Backbone.js n00b and trying to get my head around it. I know how to render a model using a view and the built-in underscore.js templating engine. Now I'm trying to render a collection and that's where I get stuck. There is no server here, so I'm not fetching anything remotely, just a simple HTML page with some JavaScript.
ContinentModel = Backbone.Model.extend({});
ContinentsCollection = Backbone.Collection.extend({
model: ContinentModel,
initialize: function () {
this.continentsView = new ContinentsView;
this.bind("reset", this.continentsView.render);
}
});
ContinentsView = Backbone.View.extend({
el: '#continents',
template: _.template($('#continents-template').html()),
render: function() {
var renderedContent = this.template(this.collection.toJSON());
$(this.el).html(renderedContent);
return this;
}
});
$(function() {
var continentsCollection = new ContinentsCollection();
continentsCollection.reset([{name: "Asia"}, {name: "Africa"}]);
});
It breaks on the template attribute line in the view but I'm not sure that's where I need to look. Am I supposed to render a collection or do I miss the point completely here (maybe collections are just grouping objects and I shouldn't look at it as a list I can render)?
Thanks for helping...
The problem is that when you define ContinentsView, the template is evaluated and it uses $('#continents-template') - but the DOM is not ready yet, so it does not find the template.
To solve it, simply move the template assignment in the initialize function:
ContinentsView = Backbone.View.extend({
el: '#continents',
initialize: function() {
this.template = _.template($('#continents-template').html());
}
...
Regarding collections, yes, they are grouping objects, specifically sets of models.
You should make the code so the models (and collections) do NOT know about the views, only the views know about models.
ContinentModel = Backbone.Model.extend({});
ContinentsCollection = Backbone.Collection.extend({
model: ContinentModel,
// no reference to any view here
});
ContinentsView = Backbone.View.extend({
el: '#continents',
initialize: function() {
this.template = _.template($('#continents-template').html());
// in the view, listen for events on the model / collection
this.collection.bind("reset", this.render, this);
},
render: function() {
var renderedContent = this.template(this.collection.toJSON());
$(this.el).html(renderedContent);
return this;
}
});
$(function() {
var continentsCollection = new ContinentsCollection();
continentsCollection.reset([{name: "Asia"}, {name: "Africa"}]);
// initialize the view and pass the collection
var continentsView = new ContinentsView({collection: continentsCollection});
});
It is also worth noting there are additional complexities that quickly rear their heads when rendering a collection in a view. For instance, the view generally needs to be re-rendered when models are added or removed from the collection. It isn't rocket science to implement your own solution, but it is probably worth looking into existing solutions since there are quite a few tried and tested ones out there.
Backbone.CollectionView is a robust collection view class that handles selecting models in response to mouse clicks, reordering the collection based on drag and drop, filtering visible models, etc.
Several popular frameworks built on top of backbone also provide simple collection view classes, like Backbone.Marionette, Chaplin, and Layout Manager.
Even though Backbone itself does not provide any structure for rendering a collection, it is a non-trivial problem and lots of people have different opinions on how it should be done. Luckily it is such a common need that there are quite a few good options already in the eco system.