I have the following fragment in a web component:
<div id="mycodes">
<template iterate='code in codeList'>
{{code}}
</template>
</div>
And in a Dart file, codeList is populated when the user clicks on a button:
void onMyButtonClick(Event event) {
HttpRequest.getString('http://getData').then((response) {
mylist = json.parse(response);
for(var code in mylist){
codeList.add(code['c']);
}
}
The problem is that I don't see data on first click. I need to click the button twice to see data.
But if I fill codeList manually (not from network data) as shown below, then I see the data on first click:
void onMyButtonClick(Event event) {
codeList.add("data 1");
codeList.add("data 2");
}
}
I need the template to iterate after the network data is available. It appears that event loop has already done its job of painting a page before the network data becomes available through future object.
Is there a way to refresh the page after model is updated in dart?
The reason your codeList currently populates if you add it with the on-click event is because the current web_ui has 'watchers' which automatically are called when an event happens. You then populate the list synchronously. However one of the downfalls of watchers is exactly your use case, when the data is updated asynchronously then the watchers don't reflect changes in time.
As a result the watchers are being phased out and replaced with observables. Observables allow us to flag a variable to be watched for reassignment and when that happens it will cause the view to change. For example:
#observable int x = 0;
// ...
x = 1;
When the x = 1 is called later in the code it automatically triggers the views to update. This leaves us with one problem however. When you are adding to a list, you are not reassigning the value itself. As such, observables also offer a function to convert a list to an observable list (this also works for maps).
For instance if you changed your declaration of codeList to something like the following, then when you add to the list later it will update accordingly.
var codeList = toObservable([]); // Assuming it starts with an empty list
// or
var codeList = toObservable(_startCodeList); // if you already have a list
Also see the Dart Tutorial: Target 7 for more information on using #observable and toObservable.
For more in-depth information, check out the article on Observables and Data Binding
You need to mark the fields you want WebUi to monitor with the #observable annotation. Otherwise you only get the initial value not any subsequent updates.
You can do this either directly on the object declaration or you can make the entire class as observable and all its fields will then be observed.
For an example see http://www.dartlang.org/docs/tutorials/custom-elements/#using-two-way-data-binding
Related
I have been scouring the web for a clear answer on how to query for an element generated by a dom-repeat element from Dart code.
sample.html
<dom-module id="so-sample>
<style>...</style>
<template>
<template is="dom-repeat" items="[[cars]] as="car>
...
<paper-button on-click="buttonClicked">Button</paper-button>
<paper-dialog id="dialog">
<h2>Title</h2>
</paper-dialog>
</template>
</template>
sample.dart
I'll omit the boilerplate code here, such as imports or the query to my database to fill the cars property ; everything works fine.
...
#reflectable
void buttonClicked(e, [_])
{
PaperDialog infos = this.shadowRoot.querySelector("#dialog");
infos.open();
}
This generates the following error :
Uncaught TypeError: Cannot read property 'querySelector' of undefined
I have tried several 'solutions', which are not, since nothing works.
The only thing I saw on quite a lot of threads is to use Timer.run() and write my code in the callback, but that seems like a hack. Why would I need a timer ?
I understand my problem may be that the content of the dom-repeat is generated lazily, and I query the items 'before' they are added to the local DOM.
Another advice I didn't follow is to use Mutation Observers. I read in the polymer API documentation that the observeNodes method should be used instead, as it internally uses MO to handle indexing the elements, but it again seems a bit complicated just to open a dialog.
My final objective is to bind the button of each generated model to a dedicated paper-dialog to display additional information on the item.
Has anyone ever done that ? (I should hope so :p)
Thanks for your time !
Update 1:
After reading Gunter's advices, although none of them actually worked by themselves, the fact that the IDs aren't mangled inside a dom-repeat made me think and query paper-dialog instead of the id itself, and now my dialog pops up !
sample.dart:
PaperDialog infos = Polymer.dom(root).querySelector("paper-dialog");
infos.open();
I now hope that each button will call the associated dialog, since I'll bind data inside the dialog relative to the item I clicked ~
Update 2:
So, nope, the data binding didn't work as expected: All buttons were bound to the item at index 0, just as I feared. I tried several ways to query the correct paper-dialog but nothing worked. The only 'workaround' I found is to query all the paper-dialog into a list and then get the 'index-th' element from that list.
#reflectable
void buttonClicked(e, [_])
{
var model = new DomRepeatModel.fromEvent(e);
List<PaperDialog> dialogs = Polymer.dom(this.root).querySelectorAll("paper-dialog");
dialogs[model.index].open();
}
This code definitely works, but it feels kind of a waste of resources to get all the elements when you really only need one and you already know which one.
So yeah, my initial problem is solved, but I still wonder why I couldn't query the dialogs from their id:
...
<paper-dialog id="dialog-[[index]]">
...
</paper-dialog>
#reflectable
void buttonClicked(e, [_])
{
var model = new DomRepeatModel.fromEvent(e);
PaperDialog dialog = Polymer.dom(this.root).querySelector("dialog-${model.index}");
dialog.open();
}
With this code, dialog is always null, although I can find those dialogs, correctly id-ied, in the DOM tree.
You need to use Polymers DOM API with shady DOM (default). If you enable shadow DOM your code would probably work as well.
PaperDialog infos = new Polymer.dom(this).querySelector("#dialog")
I'm having trouble with a knockout model that is not binding on a subscribed update. I have a C# MVC page that delivers a model to the template which is parsed to Json and delivered raw as part of a ViewModel assignment for ko.applyBindings. I have a subscription to an observable that calls a method to perform an update of the viewModel's data. Irrelevant stuff pulled out and renamed for example usage:
var myViewModel = function (data) {
var self = this;
self.CurrentPage = ko.observable();
self.SomeComplexArray= ko.observableArray([]);
self.Pager().CurrentPage.subscribe(function (newPage) {
self.UpdateMyViewModel(newPage);
});
self.UpdateMyViewModel= function (newPage) {
var postData = { PageNumber: newPage };
$.post('/Article/GetMyModelSearchByPage', postData, function (data) {
ko.mapping.fromJS(data, {}, self);;
});
};
When I perform logging, I can see all of the data, and it all looks correct. The same method is used to produce both the initial model and the updated model. I've used this technique on other pages and it worked flawlessly each time. In this case however, I'm looking for it to bind/update SomeComplexArray, and that's just not happening. If I attempt to do it manually, I don't get a proper bind on the array I get blank. I'm wondering if there is something obvious that I'm doing wrong that I'm just flat out missing.
Edit: I don't know that ko.mapping can be pointed to as the culprit. Standard model changes are also not affecting the interface. Here is something that is not working in a bound sense. I have a p element with visible bound to the length of the array and a div element with a click bound to a function that pops items off of SomeComplexArray. I can see in the console log that it is performing its function (and subsequent clicks result in 'undefined' not having that function). However, the p element never displays. The initial array has only 2 items so a single click empties it:
<p data-bind="visible: SomeComplexArray().length === 0">nothing found</p>
<div data-bind="click: function() { UpdateArray(); }">try it manually</div>
-- in js model
self.UpdateArray = function () {
console.log(self.SomeComplexArray());
console.log(self.SomeComplexArray().pop());
console.log(self.SomeComplexArray());
console.log(self.SomeComplexArray().pop());
console.log(self.SomeComplexArray());
});
Edit 2: from the comment #Matt Burland, I've modified how the pop is called and the manual method now works to modify the elements dynamically. However, the ko.mapping is still not functioning as I would expect. In a test, I did a console.log of a specific row before calling ko.mapping and after. No change was made to the observableArray.
I created a test of your knockout situation in JSFiddle.
You have to call your array function without paranthesis. I tested this part:
self.UpdateArray = function () {
self.SomeComplexArray.pop();
};
It seems to be working on JSFiddle side.
I'm not really sure why, but it would seem that ko.mapping is having difficulty remapping the viewmodel at all. Since none of the fields are being mapped into self my assumption is that there is an exception occurring somewhere that ko.mapping is simply swallowing or it is not being reported for some other reason. Given that I could manually manipulate the array with a helpful tip from #MattBurland, I decided to backtrack a bit and update only the elements that needed to change directly on the data load. I ended up creating an Init function for my viewModel and using ko.mapping to populate the items directly there:
self.Init = function (jsonData) {
self.CurrentPage(0);
self.Items(ko.mapping.fromJS(jsonData.Items)());
self.TotalItems(jsonData.TotalItems);
// More stuff below here not relevant to question
}
The primary difference here is that the ko.mapping.fromJS result needed to be called as a function before the observableArray would recognize it as such. Given that this worked and that my controller would be providing an identical object back during the AJAX request, it was almost copy/past:
self.UpdateMyViewModel= function (newPage) {
var postData = { PageNumber: newPage };
$.post('/Article/GetMyModelSearchByPage', postData, function (data) {
self.Items(ko.mapping.fromJS(JSON.parse(data).Items)());
});
};
This is probably not ideal for most situations, but since there is not a large manipulation of the viewModel occurring during the update this provides a working solution. I would still like to know why ko.mapping would not remap the viewModel at the top level, but in retrospect it probably would have been a disaster anyway since there was "modified" data in the viewModel that the server would have had to replace. This solution is quick and simple enough.
I am using angular-ui sortable version 1.2
I want to handle the move of an item from one list to another, and update the back-end accordingly.
jquery-ui-sortable defines a bunch of events, including the receive event
From within that event handler, I cannot find a way to access the angular model item which was moved, and its new parent list.
See this codepen sample.
You can see that I can access the item via the scope() in the update event, but not in the receive event.
Any suggestions for a way to handle these moves? either via the receive event or otherwise?
Reorder the items in one list
UI sortable behaves intuitive if you have one list of items and just want to reorder the list. In this case you do the following if you have an array of objects in your controller like this:
$scope.yourObjects = [
{title:'Alabama'}, {title:'Ohio'}, {title:'Colorado'}
];
in your html you may create a list of these items by using ng-repeat:
<ul ui-sortable="sortableOptionsA" class="list items-container" ng-model="yourObjects">
<li class="item sortable" ng-repeat="item in yourObjects">{{item.title}}</li>
</ul>
where sortableOptions is:
$scope.sortableOptionsA = {
stop : function(e, ui) {
var item = ui.item.scope().item;
var fromIndex = ui.item.sortable.index;
var toIndex = ui.item.sortable.dropindex;
console.log('moved', item, fromIndex, toIndex);
}
};
As you can see, in the stop function we have access to all relevant information we need to be informed about the movement.
Connect 2 list of items
Now the problem get's a little bit complicated. UI Sortable gives us no information about the drop-targets that we can use directly in any way. If we move one item from one list to another list the following events are fired:
start: We have access to the item that will be moved including the scope of this item.
update: We have access to the item that is moved including the scope of this item.
Now the item is deleted from it's source list
removed: The item was removed from the source list. The scope is no longer valid (e.g. undefined).
received: The item is about to be dropped in the second list. scope is still undefined, we have only access to the sender e.g. the drag source.
Now the item is inserted in the target list.
update: The item is dropped at the target list. but we have no access to the item scope nor does there a target object exist in the event objects. The jQuery UI Sortable did not provide these information and the angular wrapper did not expose the target model in any way :(
stop: If all steps of the drag'n'drop process are done, the stop event is fired. But we have also no access to the items target scope or the target list.
What can we do if we want to get informed about a movement and which item was moved to what kind of list?
The item that was moved is accessible by ui.item.sortable.moved in the stop event. This is our item that was moved.
Which list is the drop-target can be determined by Angular's $watch function. We just listen to changes to the lists and know, which list was modified. One caveat: the source and the target list are changing, but the target list is changed at last (see the above event order). If we listen to the changes in this way:
$scope.dropTarget = null;
$scope.$watchCollection('lists[0].items', function() {
console.log('watch 0');
$scope.dropTarget = $scope.lists[0];
});
$scope.$watchCollection('lists[1].items', function() {
console.log('watch 1');
$scope.dropTarget = $scope.lists[1];
});
we have all information to get to know wich item was moved to what kind of list and what are the from and the to index:
stop:function(e, ui){
var item = ui.item.sortable.moved;
var fromIndex = ui.item.sortable.index;
var toIndex = ui.item.sortable.dropindex;
console.log(item, fromIndex, toIndex, $scope.dropTarget);
},
PLUNKR with a lot of debug code that shows what kind of information is available during the drag'n'drop process.
Remark: if you move one item from the 'Connected lists' to 'One sortable list' the log output is wrong - because there is no listener to the 'One sortable list' list!
I am very new to ZK framework and trying to customize few things and have struck at one point which I am not sure how to achieve that.
I have a predefined section where I need to show 2 drop down and a button and need to persist those drop down values on button click event.
This is how It has been define in Spring file
<bean id="mybean" parent="parentBean" class="WidgetRenderer">
<property name="detailRenderer">
<bean class="DetailsListRenderer" parent="abstractWidgetDetailRenderer"/>
</property>
</bean>
Here mybean is being used to show main section and I am adding my drop down using this bean while button are being added to detailRenderer.
Save button is bind to onClick event, but I am not sure how I can fetch values from my custom drop down?
I am aware about binding those Dropdown with onClick event but they have to be in same class.
Can any one suggest me how I can fetch values of those drop down.I am creating down down with following code
Listbox listbox = new Listbox();
listbox.appendItem("item1", "item1");
listbox.appendItem("item2", "item2");
This is my button code in another class
protected void createUpdateStatusButton(Widget widget,Div container)
{
Button button = new Button(LabelUtils.getLabel(widget, buttonLabelName, new Object[0]));
button.setParent(container);
button.addEventListener("onClick", new EventListener()
{
public void onEvent(Event event)throws Exception
{
MyClass.this.handleSaveStatusEvent(widget, event);
}
});
}
You may want to listen to the onSelect (I prefer to use Events.ON_SELECT rather than writing the strings) which is more specific to when the Listbox selection changes.
Either way, the key is to get the information you want from the Event passed to your EventListener, rather than going back to your Listbox itself. The basic Event usually carries useful information on getTarget and getData but using more specific events (SelectEvent in this case) will give you access to more relevant info.
button.addEventListener(Events.ON_SELECT, new EventListener<SelectEvent<Listitem, MyDataObject>() {
public void onEvent(SelectEvent<Listitem, MyDataObject> event) {
// Now you can access the details of the selection event..
List<Listitem> selectedItems = event.getSelectedItems();
List<MyDataObject> selectedObjects = event.getSelectedObjects();
}
});
You can find out what events are available for different ZK widgets in their Component Reference documentation.
If I understand the question (I don't think I did in my previous response) you want to gather information from the page (eg: Listbox selection state) when the user clicks a button. Your problem being that you are using disparate classes to compose the page and so don't have access to the various ZK Components when the button is clicked.
(Ignoring the multiple class issue for a minute)
From a high level, there are sort of two camps in the ZK community. The newer MVVM approach suggests the view should push the relevant state to the back end as the user interacts with the front end. This way, the back end never needs to ask for the client state, and when the button is clicked, the values/state are on the server ready to be used.
The other camp binds the client to the server such that the back end always has access to the client Components and when the button is clicked, the values/state can easily be retrieved by interacting with the components.
Another approach is more like what I was talking about in my previous answer, to not bind the back end to the client at all but to rely on event data as much as possible. I favor this approach where it is sufficient.
Now, you're free to choose your favored approach and ZK has lots of documentation on how to work in either of these camps. The question then is where is the client state stored on the server (either pushed there by the client in MVVM or bound there in MVC). I don't think that's a question that can be solved here, that's a software engineering challenge. I personally suggest you take on standard ZK patterns so as not to but heads with the framework. If you really want to go your route, you can grab a reference to the Listbox on the fly like so:
public class Foo {
public static final String LISTBOX_ID = "myListbox";
public void renderListbox(Component parent, MyItem items) {
Listbox listbox = new Listbox();
listbox.setId(LISTBOX_ID);
listbox.setParent(parent);
for (MyItem item : items) {
listbox.appendItem(item.getName(), item);
}
}
}
public class Bar {
#Listen(Events.ON_CLICK + " = #saveButton")
public void saveButtonClicked(Event event) {
Component saveButton = event.getTarget();
Listbox listbox = (Listbox) saveButton.getFellow(Foo.LISTBOX_ID);
Set<Listitem> selection = listbox.getSelectedItems();
// do something
}
Often, I create an element from which I need to listen to (Mouse)Events. Then, later, I don't need the button anymore, so I remove it. Like this:
var button = new ButtonElement()
..onClick.listen((_) => print("Clicked!"));
// ... somewhere else in the code or in the callback above
button.remove();
Should I also take care of the onClick subscription (to prevent memory leaks) or is that handled for me?
I suspect this will not be done automatically by removing the element from the DOM, as you might re-insert it at another point. The source code for remove() is fairly simple:
Node remove() {
// TODO(jmesserly): is parent == null an error?
if (parentNode != null) {
parentNode.nodes.remove(this);
}
return this;
}
However, if there are no other references to the object and the Element class gets cleaned up by the garbage collector, then I expect the subscriptions will go with it (though I don't know enough to know how to confirm this from the source!).