My attempts at trying to stick with the MVVM design pattern has left me spinning in my tracks. I have a view that is a pick list of site locations. I have a viewmodel that the view gets its data context from and I've bound some items to it with buttons and such (yay!).
Now I'm trying to switch the current view from a button click from within the view.
By clicking on the "start maintenance" button I would like to switch the view to another view with a different viewmodel.
So I know MVVM is just a design pattern and there seems to be a bajillion different ways of implementing navigation with MVVM. But the majority of these solutions I've seen point to having a main navigation pane and that is not what i am intending to do.
I plan on now trying to use a viewmodellocator with MVVM light messenger pattern to try and get my views to change. But after spending the past 3 days trying to shoehorn this thing to work, I'm growing desperate. Are there any other suggestions on how to implement this? I do like Sheridan's answer to a similar post:WPF MVVM navigate views because it avoids using a toolkit/framework. But I think the answer was perhaps too vague for me and I couldn't implement it because I didn't understand how to change the views (Sheridan's custom relay message was hard to follow as a novice).
Help please you Internet Denizens! :) If you could point me to any examples that would appreciated as well!
A big thank you to Rachel! I created a mainviewmodel that instantiates the other view models in my app. Then I used MVVM light to send a message using a template of a generic object to stuff the message between the models which then allowed me to handle the message in my main view model and switch the viewmodel context!
Thanks for all the help!
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Someone asked me to implement MVVM in Unity and I'm sure they were not happy with my version, so I'm trying to clear things out and improve.
I know what MVC or MVVM stands for. But in Unity the "View" and "ViewModel" blur in scope. I'm not sure what does specific developers expect when they want to see a "ViewModel" in Unity.
It's more of a clear separation for MVC in Unity for me, but I have no idea what people expect when they want to see a "ViewModel".
Does it mean the Button will also have the logic script? Which sometimes seems like a horrible break of SRP when your button also initializes bullets.
Question: How to utilize MVVM in Unity?
Thank you.
ViewModel:
I'd expect a ViewModel to:
Be a component.
Contain properties.
Allow Views to be subscribed to receive updates whenever the value of a property changes.
View:
A View in Unity on the other hand would be a component that causes something to be drawn on the screen, or is used for receiving the user's input, such as a Button or a Renderer.
The command pattern can be used to handle button clicks in MVVM: bind a button to an ICommand or delegate type property in a ViewModel, and execute it when the button is clicked.
I am using a NavigationWindow to house my pages in this WPF application. I am just learning MVVM with WPF and have been looking for a good solution to navigating pages while maintaining MVVM.
I have a LoginViewModel that does all SQL database credential checking, once the credentials have been verified against a Password Hash I want to navigate to a new page depending on who logs in.
I am looking for some suggestions or common answers to this solution. I have done a lot of research and keep seeing IOC containers or an application view model? I wanted to get some other opinions on the matter and possibly a point in the right direction!
Thanks!
I would suggest using a framework to achieve the IOC container solution. Mvvm light for example uses a ViewModelLocator to store its ViewModels.
An example for page navigation in MVVMLight can be found here.
I currently have a viewmodel such that it has a grid full of appointments. I would like to double click and open up my CalendarView with the editappointmentdialog opened for the record that was selected. May I ask how would I do that in an MVVM style?
I searched the internet and found this RadScheduleViewCommands.EditAppointment.Execute(appointment, this.scheduleView); but I don't have access to the scheduleView object from the MVVM. May I ask how abouts I should do this?
I think I can achieve this if I relay it back to the view, but I'm trying to look for another approach.
The issue you have is that you can't open a view from a view model as it'll break the MVVM design pattern.
There are a couple of ways you can open a view from the view model without too much hassle:
Implement a Messenger service to publish an event to the view, like MVVMLight does.
Straight up add a Click event handler on your button and open the view in the code behind (It's still view code after all).
However my preferred method is to use an ICommand, or RelayCommand. I have written a repository on GitHub which demonstrates how to achieve this.
I'm developing a WPF based MVVM application and have a question relating to the best way of approaching view navigation within my application. Specifically, I am interested in the cleanest way to approach this navigation when I have multiple views that can cause navigation.
Let me summarize my current application layout so that I can better explain the problem.
The diagram above shows the rough layout of my main shell. The Main Navigation area is static and provides a number of buttons. Buttons exists for primary application functions such as Status, Configuration, Diagnostics etc. When one of these buttons is pressed, the content of the Contextual Navigation area is set. Specifically, this achieved by having the contextual navigation area contain a content control with the Content property bound to a single property of type ViewModelBase. In addition, the view models and views are tied together with data templates in the application resources.
The specific view/viewmodel populated in the contextual navigation content control then provides addition navigation options that are relevant to the primary function selected in the main navigation. When an option is selected in the contextual navigation, the main content region is updated in exactly the same way as described with the contextual navigation previously.
So I suppose you could describe the combination of MainNavigation and ContextualNavigation areas something very similar to an Outlook Style menu bar. i.e. primary selection at the bottom, secondary selection at the top, resulting in a change in main content area.
Now to the problem. I can make this work, but it's starting to get very messy! I've got the MainNavigationViewModel causing navigation, and multiple contextual ViewModels that get populated in to the ContextualNavigation area causing navigation. On some occasions, it may be that an action in the main content area also creates the need for navigation also. I've also actually got a Ribbon control that may also cause some navigation. So I've got navigation everywhere spread throughout my ViewModels and I don't believe that it is maintainable. PS. In case you were wondering, I'm currently using a messenger system to allow decoupled communication between view models.
I'm starting to think the best approach is to create an abstract service that takes care of navigation for all the view models within my application but not sure what that would look like. Am I on the right lines here and if so, does anyone have any suggestions for an application wide navigation service that handles navigations from multiple view models?
first of all what MVVM approaches are you using? View first or View Model first?
the right choice can make you life easier.
The idea you already have go's into the right direction Interfaces and inheritance - abstracting the navigation layer.
if you already use Messanger it's actually follows a similar approaches.
in your case an architecture plan would be more than necessary, take yourself time and draw it down.
Can someone please help me work out how to open a Dialog Window,
the simplest scenario I can think of is:
We have a main window with a button and a Label,
when the user presses that button,
a dialog window with a text box and 2 buttons appear,
one button says submit,
when the user presses submit it closes the window,
it changes the color of the mainwindows background to red,
and takes the input placed in the textbox and changes a label on the main window to that content(I am bot so much worried about this part I get how to do this part),
while the other button just cancels the operation,
Assume that the Datacontext of the MainWindow and DialogWindow is MainWindowViewModel and UserInputViewModel respectivily.
Now on this link Cameron talks about using a service, ie IDialogService and DialogService
now could someone please explain to me how to implement those methods in the scenario above? Or if there is another way to do this then please let me know?
Please don't link me to any to any pages because I've probably read them all and I can't seem to get a clear understanding of what is meant to be happening?
~Slowly loosing his sanity because MVVM makes things so much harder :(
Not really an answer, but I think I'll add my POV anyway. How to use dialogs in an MVVM way, is something no one has really managed to do in an elegant fashion yet. There's basically 3 camps:
(1) The people who use an dialogservice like you described,
(2) The people who thinks that MVVM is good, but not something you should spent countless of hours trying to get right, so they use the codebehind, and
(3) people like me, who thinks that more often than not, the dialog and the parentview are so tied together that they should share viewmodels (as-in, the dialog is just one way of showing the data from your viewmodel).
The learning curve for MVVM can be slightly steeper when attempting to do something a little more advanced than simple data binding. Have you checked out the MVVM Light toolkit? It includes a Messenger class that facilitates sending messages around the place. A listener registers for messages they want, and a sender just publishes them. In this manner, neither the listener or sender know about each other, but can communicate. Meaning the View can register for a message, and the ViewModel can send one.
This question talks about doing something very similar to what you want to do. I recommend the MVVM Light toolkit by the way!
I'm not sure about how you use the results of a dialog to send them through to the ViewModel. I'm assuming the harder part for you is communicating from the VM to the View.