I have strange (at least to me) problem with multiple checkboxes with v-model. When using multiple checkboxes that are v-model'ed to one property then normal array is produced which is done with code below:
.form-check
input.form-check-input(type=“checkbox” name=“checkbox” v-model=“methodology” value=“issue tracking tool”)
label.form-check-label issue tracking tool
However, when I try to move it to Single File Component I had to copy some magical tricks from Vue.js forum to make it work. I still suspect that there must be easier way to achieve it. I can’t imagine that it wasn’t solved with simple solutions since it’s quite a common pattern (checkbox in a component - nothing exotic, right?). Any help appreciated!
Here is the working jsfiddle - please have in mind that there is no errors. I just want to know if that really has to be that complicated.
The answer is, no. You may be able to do this magic differently, but it needs to be done.
Vue has to do magic behind the scenes for checkbox because unlike all the other inputs, which have a single item that gets updated, the checkbox has to manage whether the a value is in an array. This means that the listeners and values have to be patched between the wrapper and input.
I was able to get Aurelia-validation working on a dynamically created form when using the compose element, but I've switched to custom elements for better encapsulation and reuse of the custom controls. However, now my validation seems to be half-broken.
https://gist.run/?id=6e97538c3888cae0f6134faed9d67362
Issue 1: The ValidateBindingBehavior is not doing anything. I suspect it's not finding the controller or matching the rules since the property name is not easily visible in the binding (due to dynamic controls).
Issue 2: For some reason validate() on submit actually only shows the first error instead of all of them. That indicates a problem but I don't know what.
Can anyone get the attached GistRun to work properly?
I have an elm app designed with the Elm Architecture in mind. I've used it for all the samples in the tutorial and they work fine. I have the following components
ContainerListView
ContainerView
AddressView
RegistrationView
...
The ContainerView component is a very formatted div structure that is used to contain other views (but for now, only 1 at a time)
ContainerListView can contain multiple containerViews. It handles their presentation and positioning. You can think of it as an MDI surface
A menu from the main ui is used to add new container views to the container view list.
I'm presented with with three main questions. Two of them are
How do I create the components such that Container view can contain any other element is I pass in for example the init, update, and view functions and expect all things to be wired correctly? At the moment, the samle views I have are kinda hard-coded. They know exactly who the children is.
Some of the components require access to things like url, access token, etc. Does this always have to be passed in from main to the individual components or it can come from another source which will essentially be readonly and maybe updatable only from main?
I'm not sure if these two should be individual questions on their own. Any information on how to architect larger apps beyound hello world will also be appreciated.
I'm working on something similar! Nested controls. I too have a container object which knows about all the types that it can handle, and has basically case statements to handle each type. So I can't drop in a new control type and expect it to handle it, that requires altering the container.
As far as I know elm doesn't have type classes, which would be how I might try to handle that kind of abstraction in haskell or purescript. There's more about that here:
https://github.com/elm-lang/elm-compiler/issues/38
and here:
https://github.com/elm-lang/elm-compiler/issues/1039
The upshot appears to be that they don't know how they want to solve that problem yet, so they haven't.
I have a project with a number of comboboxes, all binding correctly. Since installing SL5 I started experiencing all sorts of binding issues as well as the debugger being crippled. The problem is that when you switch from SL4 to SL5 and then back to SL4, not all the references are reset. Long story sort, I had to reinstall vs2010 to fix those issues. Now I am testing the dev environment and although I can get a textbox to bind from the VM, I cannot get a combobox to bind.
What I would like to know is what is the absolute minimum requirements for a combobox to bind. My ViewModel's property SET is getting its data.I have the comboboxes ItemSource set and the DisplayMemberPath set.I have tried using the ItemTemplate syntax but nothing works. The RaisePropertyChanged is being fired. Could this be a UI threading issue? The only difference between this combobox and the others is that there is a call to the database that collects values that are then used in a second call to the database. Those results are then passed to the property in the VM which raises the RaisePropertychanged event, but the binding doesnt render. I have mocked an entity in the class constructor and the binding works, but when I load the entities from the database it doesnt work.
I found the issue. This might be helpful to others. I was instantiating a ViewModels ObservableCollecion in the Completed event of the method and then looping through the collection from the database and addng it to the collection. Binding was not happening. I moved the instantiation of the ObservableCollection to the ViewModels constructor instead and the Binding started working. Still a bit puzzled as to why the newing up of the ObservableCollection has to be in the ViewModels constructor and not in the Completed event of the method fetching the data.
At the article, WPF Apps With The Model-View-ViewModel Design Pattern, the author who is Josh Smith said:
(1) In a well-designed MVVM architecture, the codebehind for most Views should be empty, or, at most, only contain code that manipulates the controls and resources contained within that view. (2) Sometimes it is also necessary to write code in a View's codebehind that interacts with a ViewModel object, such as hooking an event or calling a method that would otherwise be very difficult to invoke from the ViewModel itself.
My question is ,at the (1), why the empty codebehind is regarded as a a well-designed MVVM.(It sounds that the empty codebehind is always good.)
EDIT: My question is, as the following, why the approach like the AttachedCommandBehavior or the InvokeCommandAction is tried to avoid the codebehind coding.
Let me explain more detail.
As far as the (1) is concerned, I would think like the following situation as from the AttachedCommandBehavior. As the Border doesn't implement the ICommandSource for the MouseRightButtonDown, you cannot commonly bind the event and the ICommand, but can do with the AttachedCommandBehavior.
<!-- I modified some code from the AttachedCommandBehavior to show more simply -->
<Border>
<local:CommandBehaviorCollection.Behaviors>
<local:BehaviorBinding Event="MouseRightButtonDown"
Command="{Binding SomeCommand}"
CommandParameter="A Command on MouseRightButtonDown"/>
</local:CommandBehaviorCollection.Behaviors>
</Border>
OR
We can do this with the System.Windows.Interactivity.InvokeCommandAction.
<Border xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity" >
<i:Interaction.Triggers>
<i:EventTrigger EventName="MouseRightButtonDown">
<i:InvokeCommandAction Command="{Binding SomeCommand}"
CommandParameter="A Command on MouseRightButtonDown"/>
</i:EventTrigger>
</i:Interaction.Triggers>
</Border>
BUT,
We use the following XAML and its codebehind having the Border_MouseRightButtonDown method, which is linked to the (2) Josh Simth said above.
<Border MouseRightButtonDown ="Border_MouseRightButtonDown"/>
I think using the codebehind as above is not bad just because the difference between these is only where binding a command or add event handler is.
What do you think about this?
why the empty codebehind is regarded as a a well-designed MVVM
Having a code-behind file which consists solely of a call to InitializeComponent() in its constructor means you have achieved purity - you have absolutely zero logic in your codebehind. You have not polluted your view with any code that rightfully belongs in the viewmodel or model. This means a couple of things:
the viewmodel (and model) is easier to test in isolation
you have achieved a good level of loose coupling, which has excellent benefits from a maintenance and extensibility perspective
The benefits really become noticeable when you have to change your UI, i.e. you switch from using a ListView to a DataGrid, or you change from using the standard Microsoft controls to using some other vendor's.
As mentioned though, it is sometimes impossible to avoid a little code in the code-behind file. What you should ensure is that the code you do have is purely UI related. As an example, if you have ComboA and ComboB, and ComboB is set in response to the selection in ComboA, then setting the SelectedIndex of ComboB from the view is fine, but setting the Items or the SelectedItem of ComboB is not - those properties are both data related and should be specified via binding to the viewmodel. The SelectedIndex property is directly visual related and somewhat independent of the actual data (and it is irrelevant to the viewmodel).
If you do access the viewmodel from code-behind in the view, you should try and do it via an interface. This means your viewmodel is injected or given to the view as an interface. (Note that the binding subsystem doesn't know or care about the interface, it will continue to bind in its normal way. What this achieves is better code, with less tight coupling). The way I code it, the viewmodel has no idea that a view exists, and the view only knows about the viewmodel as an interface.
One thing to remember though is that MVVM is a pattern, and a pattern is simply a recipe or prescription for achieving a certain result in a certain situation. It shouldn't be treated as a religion, where non-believers or non-conformers are going to go to some purgatory (although adherence to the pattern is good if you want to avoid the purgatory of maintenance hell and code smell).
If you want an excellent example of how this particular pattern helps, try writing a few reasonably complicated screens in ASP.Net, and then write the same in WPF or Silverlight, and note the difference.
Edit:
let me answer some of your questions, I hope it helps....
the viewmodel's (model of view) role , in my view, has UI logic and state of a view
The viewmodel should never have any UI logic or "view state" in it. For the purposes of this explanation, I would define view state as scroll position, selected row index, selected index, window size, etc. None of those belong in the viewmodel; things like SelectedIndex are specific to the way the data is shown in the UI (if you change the sort order of a DataGrid then the SelectedIndex can change, even though the SelectedItem is still the same). In this particular case, the SelectedItem can be bound to the viewmodel, but the SelectedIndex shouldn't.
If you need to keep track of UI session type info them then you should come up with something generic (for example, I have persisted view state before by saving important stuff into a KeyValuePair list) which is then "saved" with a call to the viewmodel (via the interface I mentioned previously). The view has no idea how the data is being saved, and the viewmodel has no idea the data is coming from a view (it has simply exposed a call through its interface).
and the view's role is displaying some contents and synchronizing the viewmodel(having databinding code)
Yes, the view's responsibility is simply to visually display data presented by the viewmodel. The viewmodel gets the data from the model (the model is responsible for making database calls or WCF webservice calls, this will usually be done via a "service", but that is a whole other discussion). The viewmodel can then shape or manipulate the data, i.e. it may get a list of all customers, but only expose a filtered version of that list (maybe the current customers) in a public property which the view can then bind to.
If the data is to be manipulated into something visual (a common example is an enum value being translated into a color), then the viewmodel still only has the enum value(s), and the view still binds to that value, but the view also uses a converter to translate the pure data to a visual representation. By using the converter the viewmodel has still avoided doing anything UI related, and the view has avoided any real logic.
The MVVM can split code and page design completely; coders just care about coding and designers only care about design. But:
I've never seen any designer who using Blend or understanding XAML.
Almost all XAMLs are written by coder himself.
There is nothing inherently bad in code-behind. For simple cases, it's fine to have it. However, UI logic can get difficult to manage in many scenarios. Encapsulating that logic in attached behaviors and view models allows us to isolate the variables (and test them) so that it's easier to comprehend and maintain.
If testability is a concern, the more of your UI logic that you can encapsulate in viewmodels and attached behaviors, the more you you will be able to verify without resorting to UI testing. (While it doesn't eliminate the need for UI Testing altogether, it does provide a first level of verification before engaging in UI Testing which will be more time/resource intensive.
I think the quoted section refers to the way data is visualized. I think they mean you should not write code in code behind that is, for example, related to how or where the data is displayed (for example something like: label1.Text = ...). Doing things like that using bindings makes it easier to separate design and code (what happens if you need the data to be displayed in a text box named "tbTest" in a later version? You'd have to change your code behind).
They are not saying that you shouldn't have any code in code behind - they are just saying that in an ideal world, you'd only react to events or process data that could not otherwise be processed.
At least that's what I understand from the section you quoted.
The MVVM pattern is powerful but I find it too 'Purist'. I can see benefit is having the code behind handle all the commands and properties in the view while the ViewModel is concerned with any translation to business model properties.
A benefit of this is that if you wish to change the user UI, perhaps from desktop to browser it is likely to be just replacing the View and its code behind.
Just my thoughts!!