I have yet another question:
Why is that if I repeat over a list of objects from a template the element in the template cannot see the object when used declaratively?
artists = [ {name: 'whatever',..},...];
Example:
<template repeat="{{a in artists}}">
<artist-record model="{{a}}"></artist-record>
</template>
If I do the same imperatively it works
Example
artists.forEach(function(a) {
var node = document.createElement('artist-record');
node.model = a;
this.$.container.appendChild(node);
}, this);
Is there a way to do this declaratively?
This works for me: http://jsbin.com/zemawugu/1/edit
Check that your array assignment is to this.artists and not artists. The binding system needs that array to be on the element prototype for the template to see it.
Related
I'm wondering, is there a possibility to have databindings "out of" a template? Say I have a <template/>-Tag somewhere which I put into the slot of a different component - that component stamps it to its context. Then I want to bind data from the root element to the <template/>-Tag. Also, event bindings (on-x-changed) don't work, because you can't assign a function which is defined in the hosting component. Any ideas?
Example:
... host
{{boundData}}
<binding-component>
<template>
{{boundData}}
</template>
</binding-component>
I don't see changes when I observe boundData in the hosting component. Is there a way to get around this? Or is firing a custom event my only chance?
If you are looking for binding a property outside of polymer something like from index.html you may bind value with element. an example ; index.html
<dom-bind>
<template>
<binding-component bound-data="{{boundData}}"></binding-component>
</template>
</dom-bind>
<script>
// set a value a string, Number or Object etc.
// Optionally wrap this code into a listener ie;
// window.addEventListener('load', e=> { ...below code ... })
var boundData= document.querySelector('dom-bind');
boundData = {} //
</script>
Now in your binding-component element has a property as boundData
hope its helps or provide more code to understand better.
I've made it work the way dom-if does it, too. Like in dom-if (reference), I'm creating a Templatize-instance which then uses forwardHostProp to handle the "inside"-properties
this.__ctor = Templatize.templatize(template, this, {
mutableData: true,
forwardHostProp(prop, value) {
// handling item updates, item being the only property
// from within the binding component
// everything else is automatically bound by templatize
this.set(prop, value);
this.update(this.item);
},
});
this.__instance = new this.__ctor();
this.root.appendChild(this.__instance.root);
This all happens in connectedCallback.
Because the Templatize-instance is passed this, it's bound to the current context as well.
Good luck!
This is the code snippet but I'm not able to understand how the observer method is working
static get properties() {
return {
selected: {
type: Object,
observer: '_selectedChanged'
}
};
}
_selectedChanged(selected, oldSelected) {
if (oldSelected) oldSelected.removeAttribute('selected');
if (selected) selected.setAttribute('selected', '');
}
connectedCallback() {
super.connectedCallback();
this.selected = this.firstElementChild;
}
full code: https://codelabs.developers.google.com/codelabs/polymer-2-carousel/index.html?index=..%2F..%2Findex#3
What is selected and oldselected and how can we do oldSelected.removerAttribute?
Are these objects of elements?
Please elaborate!
selected is property of element. It's value is some HTML element (in this case it's always img i think) so, in selected property there is always saved reference to img somewhere in html. When this property change, function _selectedChanged is called with 2 arguments. first argument is new image that is currently saved in selected and second argument is old image(previous value of selected).
further in tutorial you can see code
const elem = this.selected.nextElementSibling;
if (elem) {
this.selected = elem;
}
where is shown that const elem takes some html element and put it into this.selected.
So inside function _selectedChanged they removed html attribute from old image that was previously selected (so it was visible on screen) and added new html attribute to new image that should be visible on screen for now.
You can imagine that img with attribute selected is the only one that is shown on the screen at the time
I hope you understand my explanation. My english isn't 100% so if you have question, ask me and i can try to explain it more.
EDIT
Some example with binding and observer:
Let's say we have some paper-input which should show some results (articles for example) based on value of this input. So we have some HTML:
<paper-input value="{{search}}" label="Find articles"></paper-input>
this is primitive. Just some paper-input with value stored in search property. inside script tag:
Polymer({
is: 'test-el',
properties: {
search: {
type: String,
observer: "_findResults"
},
articles: {
type: Array
}
},
_findResults() {
this.set("articles", ['firstArticle', 'secondArticle', Math.random()]);
},
});
Explain: we defined property search and articles. Whenever property search changes, it calls function _findResults (because of observer). Function _findResults do only one thing. this.set("articles") is almost same as this.articles =. More about this can be found in documentation. So this.set("articles", ['firstArticle', 'secondArticle', Math.random()]); means it creates array and set it to articles property. and now, when we have some array that is changing everytime user enter some value in paper-input, we can add some HTML to show these articles:
<template is="dom-repeat" items="{{articles}}" as="item">
[[item]] <br>
</template>
I made also fiddle, so you can play with it and understand it a little bit more.
https://jsfiddle.net/2va41sy0/1/
Your question at the beginning was almost same in difference that they stored in some property reference to HTML object and not only just string. This is also about understand some basics of javascript and not polymer
How do I print to the console all the properties of an element I have imported into a custom element.
For example, I have a custom element my-el and in that element, I have imported a firebase-document element. I want to know the current state of the model for the firebase-document element by observing the value of all the properties of the firebase-document at a particular point in time.
my-el.html
<firebase-document id="document"
app-name="my-app"
data="{{data}}">
</firebase-document>
...
foo: function() {
...
var doc = this.$.document;
// Neither of the following "works" (see below for definition)
console.log('doc', doc);
console.log('doc.properties', doc.properties);
}
By works, I mean it does not produce the desired behavior of printing an object to the console. The object being all the properties of the doc object.
You can use console.dir(), but you can also use the %o substitution string in a standard console.log() call:
console.log( 'doc=%o', doc );
The list of substition strings is avaiable on MDN's website.
Summary from comments:
Use
console.dir( doc );
How can I trigger a refresh of the template if a member of a data-bound complex object changes?
In the template:
<other-component data="{{complexObject}}"></other-object>
In the component:
_onChange: function(newData) {
//callback from some event-system
this.set("complexObject", newData);
}
The _onChange-Method is triggered when the complexObject is changed, but newData is always a reference to the same object, just members of this object changed - because of this, polymer doesn't update the view and doesn't pass the data down to other-component.
Is there a way to let polymer know that there is indeed some new data and it has to re-evaluate the template? It is working if I create a shallow clone of newData, but that seems like a hack and could hurt performance for big objects.
I can't use the set method to change the properties of the object via the path because the change happens outside of polymer-elements and I can't control it.
Call render()
this.$.yourTemplateID.render();
Here is one working example where sibling elements are interchanging data between each other: Plunk.
Docs: https://www.polymer-project.org/1.0/docs/devguide/data-binding.html#array-binding
<template>
<button on-tap="btnTapped">change Emploees from Second</button>
second: empl: <span>{{empl.employees.0.firstName}}</span>
</template>
...
<script>
btnTapped: function () {
console.log('Second: btnTapped');
//Propagate array subproperty
this.set('empl.employees.0.firstName', 'Test');
console.log(this.empl.employees[0].firstName);
//Object set
this.set('temp.firstName', 'Test');
}
</script>
this.complexObject = _.clone(this.complexObject)
cloning & reassigning might solve this problem`
I'm learning Polymer. One item that is challenging me is updating the item of an array. I wish there was a CDN for Polymer so I could put together a fiddle. For now though, I have an element defined like this:
my-element.html
<dom-module id="my-element">
<button on-click="onLoadData">Load Data</button>
<button on-click="onTest1Click">Test 1</button>
<button on-click="onTest2Click">Test 2</button>
<template is="dom-repeat" items="[[ data ]]" as="element">
<div><span>[[ element.id ]]</span> - <span>[[ element.status ]]</span></div>
<template is="dom-repeat" items="[[ element.children ]]" as="child">
<div> <span>[[ child.id ]]</span> - <span>[[ child.status ]]</span></div>
</template>
</template>
</template>
<script>
Polymer({
is: 'my-element',
properties: {
data: {
type: Array,
value: function() {
return [];
}
}
},
onLoadData: function() {
// Generate some dummy data for the sake of illustration.
for (var i=1; i<=3; i++) {
var element = {
id: i,
state: 'Initialized',
description: ''
};
element.children = [];
for (var j=1; j<=5; j++) {
var child = {
id: i + '-' + j,
state: 'Initialized',
description: ''
}
element.children.push(child);
}
data.push(element);
}
},
// Setting an individual property value works
onTest1Click: function() {
this.set('data.0.children.0.state', 'data set');
},
// Setting an entire object value does NOT work.
onTest2Click: function() {
var c = this.data[0].children[0];
c.state = 'data set';
this.set('data.0.children.0', c);
}
});
</script>
</dom-module>
For some reason, if I update the property value of an array element (as shown in onTest1Click), the UI is updated properly. However, if I update an entire element (as shown in onTest2Click), the UI does NOT get updated. In my real problem, I'm updating multiple properties on an element. For that reason, I'm trying to update an array element and not just a property. Am I doing something wrong or misunderstanding something? Or, am I going to have to update each property value individually?
If you want to mutate an array, rather than just an object in an array (such as swapping out an entire element in an array), there are array mutation methods similar to this.set.
For example, this.splice('data.0.children', 0, 1, c) will remove the current item at the 0 index of the child array and replace it with a new one, which is what it appears you're trying to do. There's also this.shift, this.unshift, this.push and this.pop. These are all similar to their Array prototype counterparts.
One thing to note is that in your example, you're also not actually swapping out the entire object. When you grab the element from the array, mutate a field, and try and replace it with itself, you're not actually replacing it, so that doesn't actually trigger an update. And since the mutation of the field was done outside of Polymer's notification system, that also doesn't trigger an update. If you replace the item with an actual different object, it will work using splice.
https://jsbin.com/rapomiyaga/1/edit?html,output (This is a modified snapshot of Günter Zöchbauer's jsbin)
If you're not making a copy of the object/a completely new object, you'll want to update each field individually through this.set.
Yes, you are going to need to update each property value individually. When you call set, Polymer will go to the given path and check if the value has changed. If the value is an object it will compare the references (and not the subproperties). Since the object reference has not changed, it will not update the UI.