When I google "Knockout Google Maps" I find quite some KO-based Google Maps implementations. All of which I was able to find take the approach to use a custom binding handler whereas I originally intended to implement it as a Knockout component.
Examples:
http://www.codeproject.com/Articles/351298/KnockoutJS-and-Google-Maps-binding
http://www.hoonzis.com/knockoutjs-and-google-maps-binding/
https://github.com/manuel-guilbault/knockout.google.maps
Can anyone point me in the right direction why one would prefer a custom binding handler over a KO component here?
My planned use case is this:
I'm implementing a page with a list of address search results. The list so far is a KO component, each list entry is generated by another KO component which the list component repeatedly calls in a foreach binding. Next to this list of search results I need a google map showing the result entries also in the map. There will also be quite a lot of interaction between the list, the list entries and the map.
Here's what I've got so far:
var GMap = function () {
var self = this;
var initMap = function() {
var map = new google.maps.Map(document.getElementById('map'), {
zoom: 13,
center: {lat: 51.4387974, lng: 6.9922915}
});
};
initMap();
};
$(document).ready(function() {
ko.components.register('gmap', {
viewModel: GMap,
template: { element: 'gmap' }
});
ko.applyBindings();
});
#map {
height: 400px;
width: 600px;
}
<script src="https://maps.googleapis.com/maps/api/js?v=3.22"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/knockout/3.4.0/knockout-min.js"></script>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<gmap></gmap>
<template id="gmap">
<div id="map"></div>
</template>
A component and a custom handler are completely different things.
Custom binding
Basically a custom binding have access to:
the HTML component where it's used
the bound value (expression supplied to the binding)
all the other bindings in the element
the binding context of the element, from which you can acces to $root, $parent, and so on
Its definition includes two functions:
init: that allows to do the initial setup, like initializing widgets, setting event handlers and so on
update: it's called after init. In that moment you can access properties (including observable properties) through the binding, all the element bindings, the context and so on. This creates subscriptios that will call update when any of the accessed observable changes.
So a custom binding shuld be used when you need to interact directly with the DOM element, for example to modify its properties, initialize widgets, subscribe to events and so on
Component
A component is completely different. When you define a componente you must define:
a template, which is a set of DOM elements, usually with bindings
a viewmodel (usually a constructor or a factory)
When you use the component:
the viewmodel is instanced
the template is loaded
the viewmodel is bound to the template
So, a componente allows to reuse viewmodels and templates
So, what's the difference?
A custom binding has direct access to the DOM elements, allowing to interact with them, subscribe to events, modify properties, and so on
A component is only a viewmodel, and a set of DOM elements with bindings to that particular viewmodel.
So, in the case of Google Maps, which needs to initialize a widget (the map) and interact with Map events, and respond to observable propèrties cahnges, you could never use a component, because the component doesn't allow the direct interaction with the DOM elements. (Remember is a bunch of HTML elements with bindings, and the corrresponding view model, whic can't include any logic to intercat with those elements).
A custom binding usually applies to a single element (althoug it could handle its children, like foreach). In the case of Google Maps you only need the element in which you'll show the map.
A component is usually a more or less complex set of DOM elements, which are not accesible "from the outside". The only communication with the main viewmodel is done through parameters. The component cannot directly interact with the DOM elements: it must do it via ko bindings.
So, for the case of Google Maps is clear that you need a custom binding.
It only makes sense to create a component when you want to modularize or reuse a set of DOM elements, and the related viewmodel, which can also include functionality like accessing web services (via AJAX), making computations (propbaly by using computed observables), and so on. For example, a shopping cart could be implemented using a component, which would include:
the DOM elements to show the items in the cart (probably an HTML table, and some controls)
controls to modify the cart content (for example for deleting elements, or changing quantities)
a viewmodel that show the total, the taxes and so on
functionality to store the cart for later, or pay for it (which could be ajax calls to services)
In this case the cart would have a viewmodel which would include the computed observables (to show the total and taxes), the functionality to remove items, or modify quantities, or store or pay, and so on. And a concrete set of DOM elements with bindings for this viewmodel, i.e. the HTML to show the cart and interact with it.
In the case of Google Maps a component could not be used without the help of a custom binding or with the hacky use of additional, non ko, scripts.
If you wanted to show a list of places beside a map, and modify that list, you could use a component, which would include a viewmodel with the list and related functionality, and a template including an element with the Google Maps custom binding. That would make sense: viewmodel + several elements.
Conclusion
This all means that a custom binding usually have a deep interaction with the bound DOM element, while a component has a higher level interaction with the elements, which must be done through bindings.
So, they play a role at a very different level. You cannot compare or interchange them.
If you insist on doing so, you could create a beast of a binding which behaves like a component, becasue you have full control on the elements, and full acces to the view model, but that's harder to implement than a component. And probably could do the other way round also in some esoteric way.
Binding
Binding, a custom or not, is a very simple concept that covers 2 things:
A property of a UI element changes, and thus it should update an object (ViewModel)
A property of the object (ViewModel) changes, and thus it should update the UI element.
From the above if only 1 implemented, it is called One Way Binding (because if you change the UI, it will update the object but not the other way around). If both 1 and 2 are implemented, it is called Two Way Binding.
So at any time if you think you need something to do that, you would need to use binding, custom binding if the framework does not have the binding you need.
Most likely, the maps you speak of needed something like above. And it actually did because the author says this in the first paragraph:
Concretely, you can learn how to make the maps marker part of the View and automatically change its position any time when the ViewModel behind changes.
See, the author talks about 2 above: When the ViewModel changes, change the position of UI element.
Component
A component is a concept of having a reusable item that may have a UI but not necessarily, and all the code needed to make it work packaged along with it. This way it can be reused. For example, it may simply be an input UI element that only allows numbers. All the code needed for it is packaged along with the UI element.
Now the code packaged along with it may code related to bindings. It may even have custom bindings if the framework they used did not have the binding they needed. In addition it may have additional code that has nothing to do with binding.
Furthermore, a component may have a single UI element or multiple. A good example of a component with multiple elements would be a message box.
In Conclusion
Bindings and Components are separate things. A component may have bindings within it or it may have other code to make it work or both.
In the case of the maps you speak of, they have only added a feature to it: To react to changes in the ViewModel. It is not a component because it is not self contained and reusable.
They could have done it using a component. However, if they did that and said it is a KO component, it may still have KO specific binding code packaged with it along with the ViewModel and all the UI elements needed.
In my Windows Store XAML app I’m using the TreeView control from the WinRTXamlToolkit and I’m attempting to two-way bind the SelectedItem property to a property on a ViewModel.
Out of the box, the SelectedItem property is read only and this makes sense because the control supports Virtualization.
I have seen some folk work around this with things like attached properties, helper methods and so forth, a great example of which is seen in this question
WPF MVVM TreeView SelectedItem
But all of the questions/solutions are not based on WinRT and all of my attempts to rework the solution code for a WinRT app have proven fruitless.
So, my question is, is this possible in a WinRT app? What am I missing?
Thanks
I'd skip trying to come up with a bindable property globally for the view model and instead use the IsSelectedBindingPath and IsExpandedBindingPath properties of the TreeView as in the debugging tools' example of the control's usage. Then when you want to select/expand an item from the view model - use a method similar to SelectItem() in my view model where I essentially set IsExpanded/IsSelected to true in item/node view models throughout the path from the root of the view model tree and load the content of the tree if the nodes in the expected path do not exist.
I'm new to html5. I want to bind backbone collection to DOM element using rivets without extending backbone view. I got code snippets like extending adapter, using rivets.bind but i dont know how to organize everything. Can someone explain me how to achieve this in steps?
Thanks in Advance
Update: We can do this if we follow the example provided in the link of the accepted answer.
what you want to bind is the View, not the collection. The Collection is just data, an array of models if you wish. The View is what responds to user interaction, and that's where your rivets binding will be handled.
Check out Backbone.Marionette framework as its specialized CollectionView simplifies this even further, although you may go with a standard Backbone.View too.
I'm currently working on a project that involve a re-implementation of the Array class.
This object needs to be an Array for compatibility reasons, while I also need to keep control of what is written in.
I cannot seem to find any way to check property creation inside of a dynamic object in AS3. Something that would work like the Event.ADDED_TO_STAGE but, like, ClassEvent.PROPERTY_ADDED.
I override methods like push, splice etc, but I cannot control direct assignation : MyArray[i] = ...
Is such a thing even possible ?
Of course, I could make some kind of validations elsewhere, but this would involve accessing a part of the code I cannot modify.
Thanks for your time !
I'm not sure I follow you entirely but you may be looking for the Proxy class:
http://help.adobe.com/en_US/FlashPlatform/reference/actionscript/3/flash/utils/Proxy.html
An example at the bottom shows you how you can override direct assignment:
override flash_proxy function setProperty(name:*, value:*):void {
_item[name] = value;
}
Using this you would be able to dispatch a custom event that would be fired any time an item was added to your ProxyArray
I have my own custom component. This component extends from a basic container. I want to be able to access the itemRenderer instances that are being visualized. I know that the component mx:list has an internal getter that provides an array of Arrays containing the itemRenderer instances that render each data provider item. I want the same thing. Any idea how of how to do that?
To be more specific: I am setting the selected property of my dataProvider items to true or false. From the updateDisplayList funcion of my ItemRenderer I check for changes of the property and correct the border color of the selected ones. Unfortunately I have to force the updateDisplayList function. I already did this once on a ItemRenderer from a list. Only with the list it was practical because by making my own list I was able to get the list of items being rendered and therefore visualized (cannot be many). It was no overhead to go trough the rendered Items and updateDisplayList. But in this case I can have 100 items. Imagine checking and changing styles on so many items. Thanks
The Flex architects intentionally made this difficult to do, because they are properly encapsulating the component. In short, to even try to do this is a violation of good OOP principles.
That said, about 90% of the things you are probably trying to do can be done by manipulating the data item, and the remaining 10% can be done by using a ClassFactory for your itemRenderer that sets a custom property on your itemRenderer to a callback where you can look at the data available to the containing context and provide back a value based on that.
If you elaborate a bit more on your end goal, I can give you more specifics.
Edit in light of clarification:
You need to make your data object class dispatch an event when it changes (one way is to make it bindable, or just make the selected property bindable). Then, in your renderer, listen for the change event and take the appropriate action.
A second way to handle this would just be to refresh() the collection, storing the selectedItem first (if you care about that) and resetting it once the refresh has finished.
I believe you can access the itemRenderer instances through getChildAt method. Flex 3's container overrides "getChildAt", "numChildren", given that some children are logical children, while some are decorative children such as background, border and scrollbars.
Keep in mind that itemRenderer may not right away become available upon dataProvider assignment, as they may be created during the next component lifecycle. Check with the underlying container's documentation and find out which event to be listened when the renderers are surely created, so you can reliably access them.