CodePen: http://codepen.io/opnsrce/pen/hclaH
Expected behavior: You should only be able to highlight one item at a time.
Current Behavior: You can highlight multiple items
Cause: HasChanged returns true when checked by the controller during the change event.
When I run this code with Backbone 0.9.2 it works. When I use 1.1.2 it doesn't.
Did something fundamentally change in the way hasChanged works between those two versions?
I believe this is the desired functionality. A model's changed attributes change each time the model itself is set. So until you set a model multiple times it will hold onto its changes. The code you've set up here would work if that hash of changes cleared out when a different model was selected. What is actually happening is that as soon as you set a model to isSelected it will always have isSelected == true and hasChanged('isSelected'), so it will never pass the condition to set isSelected to false.
One way to accomplish what you're looking for is to change your collection method to this:
onSelectedChanged: function(modelActive) {
if(modelActive.get('isSelected') === true){
this.each(function(model) {
if (model != modelActive) {
model.set({isSelected: false});
}
});
}
}
Note that I took out hasChanged since that was simply confirming that a model had changed at some previous point. Instead I compare the actively selected model with the ones being iterated. We don't want to touch the active one. I also check to see if this method was triggered via the setting of isSelected to true because if we don't do that, every setting of the iterated models to false will trigger this method and cause problems.
The only limitation of this is that you can't select the same item to toggle it off.
Related
I not sure how to solve this issue. I am sure someone will know this very quickly.
I have an array of objects and modifying a property. I have a firebase listener 'child_changed'. When firebase is updated need to update the array. Here is the code below.
dbRefList.on('child_changed', function(snap) {
var len = this.grocerylist.length;
for(var i=len; i--;) {
if(this.grocerylist[i].key === snap.key) {
this.set(['grocerylist', i, 'selected'], snap.val().selected);
}
}
this.notifyPath('grocerylist', this.grocerylist.slice());
}.bind(this));
When the array is modified I want the template repeat-dom to trigger. I know this.set will not trigger array mutation sub properties but again I am not sure how to solve this. I done research and tried so many solutions.
I can force a render on the template dom-repeat but I would prefer the data binding way.
So this code (just the this.set you have in there now) should cause the value of grocerylist.i.selected to update inside the dom-repeat (assuming it's bound in there so it's actually showing up).
What behavior are you seeing? Are you trying to filter or sort the list based on the selected value? In that case, you might need to add observe="selected" on the dom-repeat.
(Also—have you confirmed that the child-changed callback is being called with the this value you expect—the element—rather than window or something else?)
You should be able to force a refresh by doing this.grocerylist = this.grocerylist.slice() or this.set('grocerylist', this.grocerylist.slice()); ... notifyPath doesn't work here because notifyPath doesn't change the value, it notifies the element about a prior change (the second argument is effectively ignored).
I have an entity in the scope that is being edited by the user. Each time it gets modified, I want to trigger some custom validation. So I have:
// validate the position if anything has changed
$scope.$watch("entity", function() {
if ($scope.entity.Id) {
$scope.validate();
}
}, true /* watch "by value" (see: https://docs.angularjs.org/guide/scope#scope-life-cycle) */);
So far so good. Now, since this is a big entity with quite some fields, not all of the fields participate initially in data-binding. Only portions of the fields are visible to the user by using a tab control. When the user switches tabs, another portion of the entity is shown.
However, when the additional controls get bound to the corresponding fields of the entity, the $watch gets triggered even though the binding doesn't change any value on the entity.
Why is this the case and how could I prevent it?
Note:
I thought that the data-binding is possibly adding some internal $... fields to entity but these are hopefully disregarded (at least this is the case in angular.equals so they should probably be disregarded in the $watch too, I assume).
$watch with object equality flag true compares the properties of the old object copy with the current object. Therefore the listener fires when a property name is changed, added, or removed. You can try something like the following:
$scope.$watch("entity", function(newVal, oldVal) {
if(Object.keys(newVal).length !== Object.keys(oldVal).length)
return; //Detect added properties
if ($scope.entity.Id) {
$scope.validate();
}
}, true
I have many events bound to elements in my view, though when I use stickit js to change values in my view by altering the model it doesn't trigger an onChange event.
Is there a way that I can trigger an onchange event for the current model:element after the setting the value in the model without having to write a handler for every binding? This would be for all form elements, input/select/textarea.
I want to avoid the following for each form element on the page:
bindings: {
'#foo': {
observe: 'foo',
afterUpdate: 'forceChange'
},
'#bar': {
observe: 'bar',
afterUpdate: 'forceChange'
},
...
},
forceChange: function(el) { jQuery(el).change() }
One possible hack (with version 0.6.3 only) would be to define a global handler which matches all elements:
Backbone.Stickit.addHandler({
selector: '*',
afterUpdate: function($el) {
$el.trigger('change');
}
});
Since handlers are mixed in with other matching handlers and bindings configurations in the order that they are defined, you couldn't use afterUpdate in any of your bindings without overwriting this global, all-matching handler since the bindings configurations are the last to be mixed in. You can read more about it here.
Ahhh, that comment clarifies matters. So, in Javascript when you change an input's value "manually" (whether through jQuery or through someElement.value =) the browser won't, as you noticed, fire a change event. Change events (and most other events for that matter) are only fired in response to user actions, not to Javascript.
Luckily, just as you can "manually" change a value, you can also "manually" trigger an event. In jQuery the syntax for that is:
$(yourElement).trigger('change');
If you need to control things like e.target you can read up on the jQuery trigger documentation for the details, but that's the basic idea.
You can even chain the value-changing and event-triggering together if you want:
$(yourElement).val('newValue').trigger('change');
My backbone.js model has an array property. I bound the change event to save().
After sync() (triggered by save(), my app server returns an identical JSON, but backbone thinks the array has been changed (due to a different reference to the array I guess?), and trigger changes again. Then an infinite loop occurs.
save() -> sync() -> triggered `change` -> save()...
What shall I do?
Idea: I can bind the change event to a function that checks if the changed attributes are of type object/array, and do a deep comparison and call save only if the array/object really changed. If true then save()?
Thanks!
Try the Edge version of Backbone (master branch) this behavior changed after 0.9.9 - see https://github.com/documentcloud/backbone/pull/2004
Backbone has a special option on many methods to prevent just this sort of issue: silent:true. If you pass that option to your save method, the resulting sync won't trigger a change event.
So, if you want to set your change event handler to save silently, something like:
changeHandler: function() {
this.save({silent:true});
}
should do the trick.
The Backbone documentation says:
Model.set will fail if validation fails - it won't set the value therefore it won't trigger any callback. We can pass { silent: true } to Model.set - then it will set the value but won't trigger any callback neither.
So,
Why does Backbone Model require a valid state to simply set an attribute value? What if we want to set attributes as the user interacts with the UI, but the model is not valid yet? It means change callbacks are unavailable unless we pass { silent: true } then manually trigger the change?!
Please say you know a better way of handling this :)
I'm not sure how to answer the Why questions but you could say that there are arguments for why it is good that set runs validations. For instance, it makes it dead simple to do client side validation in real time.
If your problem could be solved by only validating the value that is currently being changed by the user, you can do that by combining your validate method with the hasChanged method.
For example something like this:
Backbone.Model.extend({
defaults : { name : "" },
validate : function (attrs) {
var errors = {};
if(this.hasChanged("name") && attr.name.length == 0) {
errors.name = "Need a name yo!";
}
//...
if(_.keys(errors).length > 0) {
return errors;
}
}
})
In Backbone whenever you call set on model , It keeps track of what attributes of model has been changed and what attributes are newly added.Calling validate allows it be more efficient in doing it .Passing {silent:true} as options in set function causes validate and change to not execute so if doesnt fire any change events.
If you want to set attributes as the user interacts with the UI, but the model is not valid yet
In this case you can set the change in a plain object make sure object keys are sames as model's attribute and then at some point just set in your model.
var uiChanges = {name:'x'}; //just fill it with your changes
ur_model.set(uiModel); //then set it ,this way it fires change events only once
To check the diff between your plain object and model you can use the
ur_model.changedAttributes(uiChanges);
changedAttributes -
Return an object containing all the attributes that have changed, or false if there are no changed attributes.
You can further use it save only those attributes that have changed rather than saving entire model again.