So I'm planning on writing an application that is largely a windowless application. There will be windows for user interaction, but only at the request of the user. Otherwise the application sits in the system tray and runs a timer, executing some logic every minute or so. My question is this: As far as I can tell, I would put all the related logic in App.xaml.cs (starting the timer, executing the logic at each interval), but for some reason this seems wrong to me.
The app will have a system tray icon that users can interact with to get details, adjust settings, etc., but otherwise the app just sits there and does what it does. Is it appropriate to put all the code in the code-behind for the App.xaml class? I don't know why, but it seems as if I shouldn't, and there should be somewhere else, but I can't really think of anything.
I've never written an app like this before, hence my ignorance. Any advice would be greatly appreciated. Thanks.
James
Even with applications where most interaction is done through windows it's usually a bad idea to put all the code in the code behind. Interactions are often initiated eventhandlers in the code behind but you can put your code in classes you create yourself.
The same goes for applications that do not show a user interface most of the time. Most of the actions will be initiated from the App.xaml.cs but that doesn't mean all the code has to live there. You can encapsulate timers in their own classes that can kick off other code to do work for example. Divide your code up along lines of responsibilities, a window class does UI stuff, domain logic goes into other files etc. That will enable you to create more maintainable applications.
It doesn't sound like the code belongs there, and at most just a call to start the timers.
What does sound like a perfect fit for your issues, is the M-V-VM (Model - View - ViewModel) pattern. As you noteded, it also will 'feel' more correct then attaching logic to your code behind. Using MVVM you can separate your sparse UI into a View, and your code can exist separately in the Model and ViewModel.
I would recomend using the toolkit here, as it also contains good overview documents and a sample you can digest as you create your own solution. Laurent Bugnion has also released a MVVM starter toolkit that you could use to get started.
Also, here is some good stuff to get you started on actually setting up your controls in the system tray.
Related
I'm trying to get into WPF and have been reading articles saying MVVM is generally the way to go for WPF.
What about application that doesn't require user interactions such as button clicks?
An example would be a Card reader application:
User connect card.
Application read and display card info on screen.
Perform backend validation.
Display result on screen.
I could be wrong but I don't see MVVM being suitable for such application. Is there a more suitable design pattern that I should be considering instead?
The point of MVVM is to detach your views from your code.
Lets say in a month you need another view, you can easily create one without having to worry about "logic" being part of the view.
Mind you, some things are still easier done in the code behind ... but depending on your "purist" status, it'll vary.
Having said that, you can still happily use MVVM for your card application, and use the GUI to switch around and show different views ...
Last thing is I'll recommend picking an MVVM framework to help you jump start. There's plenty of them out there, varying in complexity and goals.
MvvmLight , Castel (?), Prism, Micro mvvm (?) ... run a quick search and see which you like .
Having said the above, let me shamelessly plug this article: The big mvvm template
I am building a WPF application and using the MVVM for the first time. Overall using MVVM has been very interesting and one of the major benefits is the nice separation between the view and the model classes. It kind of disciplines (at least young developers) to not to mix them together.
We have a scenario where a window needs to be closed on a button click after a confirm message box. Now this can achieved the old-way by handling the button click event and closing the window in the Window class itself. Or we can do it MVVM way by creating a command in ViewModel, call Window to show message box..etc.
I understand what needs to done here, but my question is - is it necessary to use MVVM commands in all cases? Are there exceptions where we should not use commands e.g. simple UI actions? Are we not overusing MVVM here? What exactly will the benefits doing everything the MVVM-way?
Or we can do it MVVM way by creating a command in ViewModel, call Window to show message box..etc.
Let me pick this apart, mainly because IMVHO I see this done wrong all the time - a lot of people try to do too much in the VM. First of all, ask yourself the question:
Is the prompt related to the data or business rules in any way whatsoever?
If it isn't, i.e. it is simply a "are you really sure?" type prompt, then this SHOULD be done purely within the code behind of the view. The only time the viewmodel needs to have any knowledge or take any action is when it actually has something to do with the viewmodel, in which case you should expose a command from the VM, but the actual window closing is still done from the code behind of the view.
The VM should know nothing about the view that it is bound to, that is one of the purposes of the MVVM pattern. It can expose commands, but it shouldn't know that a user has interacted with a specific UI element1, and it shouldn't directly know that the window is about to be closed. It is okay for the VM to prompt (via a dialog service, which you do have, yeah?) that the current data is unsaved, but it doesn't know about the window in general because it doesn't know how its data is presented.
Sometimes you will walk a fine line, and it is easy to over analyze whether something should be done purely from the view, purely from the VM, or as a mixture of both. If you remember the role of the VM, and remember that it is okay to have code behind in the view (provided it is only doing view related stuff and handing VM stuff off to the VM) then 99% of the time you won't have a problem.
1 For example, the VM shouldn't know or care whether the user just clicked a button, hyperlink, or touched a hot spot in an image. The same command can be used to handle any of this.
When I first learned about Microsoft's then-new framework for developing desktop applications, WPF, I thought that one of the biggest benefits of it would be its efficiency. After all, I already know what the GUI controls and elements were that I wanted to use--I just have to slap them all on the page and then wire up all my bindings right, and I'll be done. After that, I learned about the MVVM pattern, which promised clean separation of concern within my WPF app.
I thought this was going to be great! I got into creating several different admin and data entry WPF apps with my team at work, and thus I began to crank out working software with robust but simple GUIs, right?
Not so fast, there, cowboy coder. My experience is that writing WPF is S-L-O-W.
Well, at least the way I do it. You see, after I have a picture of my GUI on a whiteboard, I code up the XAML with the controls that I want. This part, as expected, is fast--laying out the whole of a window is pretty quick. After that, its all the little stuff you want these elements to do takes awhile. I always seem to want to make this text bold in some cases; show a red error box in these other cases.
Then things unravel: this binding isn't working right over here--I have to write a converter and adjust the layout for the right values. Whoops, I forgot that extra NotifyPropertyChanged there. Oh, and I want to use a different template in this state vs. that, so I have to figure out what I can use to swap the templates in certain situation. This data is coming in asynchronously, so I need to make sure the right thing is happening on the right thread and that Property gets NotifyChanged as well. Crap, when I maximize my window, it doesn't stretch like I thought it would--must be because its container height isn't defined, but I don't want to define that, so I have to make it stretch in its parent. Oh, now I really want to make a user control out of this stuff over here, so I better implement some dependency properties...
On and on I go, spending hours and days on stuff that just feels so small and minor. I soon resort to cutting usability features and look-and-feel enhancements because this is taking just too darn long.
Does anyone have any tips or principles I need to try in order to write WPF efficiently?
A couple of things that have saved a lot of time for me:
Use DockPanel as your default panel for layout unless you have a good reason not to.
Keep a folder full of useful classes: a ViewModelBase class that implements INotifyPropertyChanged, a RelayCommand class, etc. There's no need to get fancy and try to make this a separate assembly that you build into your project; just write reasonably good implementations and copy/paste them into your new projects.
Get Resharper and use it. Use templates for creating dependency properties, properties that do change notification, and commands.
Find or build a good library for asynchronous task management.
I find that even for very simple applications I get more done faster with WPF than I did with Windows Forms. For applications that aren't very simple, there's absolutely no comparison.
For the most part, WPF applications are a lot of work to develop because it's harder to make the case for cutting out UI features. You can't just say, "Oh, that's not possible," because it probably is possible (whatever "it" is).
Write your own library, or find an existing one.
WPF is great, but out of the box it is missing some things that would make coding faster. I got tired of writing the same things repeatedly, so I ended up creating my own library full of things like converters, visual tree helpers, attached properties, custom controls, etc., and since then, my development time has sped up considerably.
In addition to my own library, I've also started using Microsoft's Prism and Galasoft's MVVM Light Toolkit. Both contain useful objects that I use all the time and are better than what I could code on my own. (Most used are NotificationObject from Prism, RelayCommand from MVVM Light Toolkit, and EventAggregator or Messenger from either one depending on the project, etc.)
Another thing I've done to speed up coding time is to take advantage of Visual Studio's macros. For example, to create a property with Change notification, I write the private property, hit Ctrl+E, Ctrl+R which generates the public version, then run a macro which automatically sets up the PropertyChanged notification in the setter method.
I almost never change the setter methods from the default macro'd one, and instead use the PropertyChanged event to handle any changes that should occur on the setter. This not only makes it easier to track application flow, but also greatly reduces the time I used to waste browsing through my public properties to alter a setter method.
I believe the right answer isn't for WPF at all, but it can fit what you're looking for.
Most of the times, when you want to leverage a new technology there's a time while you're not efficient, productive and your solutions aren't that impressive, innovative or just doesn't look like others.
What will give you more efficiency is working with WPF itself.
It's more about project management topics than programming. After finishing some project, your team and you should go to some room and discuss:
Success stories.
Problems during development.
Pros and cons.
Fails in the application architecture.
Communication problems within the team and customer.
... and so on.
If everyone shares their knowledge, project manager or team leader does a good job documenting each project story, finally everyone will have a "know-how".
In addition, it's important that you won't need to reinvent the wheel for every new project: if some pattern worked fine, do the same way next time, even if it's not the best way of doing it. And try to enhance it, if possible.
Design patterns, technologies, paradigms, languages, companies, colleagues and nothing are a silver bullet: Microsoft said WPF is a step-forward in Windows client developments, and it is that: a more modern approach to provide shinny user interfaces and a programming paradigm that fits nowadays' desired approaches, easing the relation between coders and designers, as WPF has XAML, which allows not only separation of concerns, but separation of professionals by area (designers, UI programmers, business programmers, ...).
Finally, as I said above, WPF won't be your silver bullet: learn from your own success and read a lot, see sample applications, download open source solutions, listen your colleagues, drink a coffee and, after all, after some headaches, some day in the near future, you'll leverage these technologies (and many others).
EDIT
I'd like to add that a good way of using the know-how is creating a Visual Studio guidance pack, so you can automate a lot of tasks like creating managers, views, models and other things just in the way your team would do by hand.
For example, you can create a guidance pack for a WPF CRM-like application and you can automate module creation. When you want to add a new module, guidance pack starts a process which adds all the necessary classes to start development this new module, and it can create a sample form already associated with a navigation manager, controller or whatever (it's just an example).
Guidance pack and T4 would be both good tools for automating tedious or repetitive tasks in everyday's tasks:
http://msdn.microsoft.com/en-us/library/ff631854.aspx
http://msdn.microsoft.com/en-us/library/bb126445.aspx
I have been using WPF since 2008 and can honestly say to do it right and clean does take more time than the same thing in WinForms would take to develop. I have written a lot more WPF than Winforms. That being said - if I need a simple internal utility - it is ALWAYS Winforms. If I have something forward facing to a client - it is always WPF. Why? Winforms are cheap and dirty and you get a lot for free. What you don't get is the fit and polish that WPF can provide. The flexibility with WPF does come at a cost - but in the longer run it's worth it for public facing software.
Yes WPF is a hurdle but it also has rewards. You are on the right track with a design pattern such as MVVM. Sounds like you have not even gotten to the "rewards" of dependency properties or event bubbling. But the control over the UI is great. Almost everything is a content control. In forms I was always writing custom controls to get the UI I wanted. In WFP I have never had to write a custom control for UI and doubt I ever will. The syntax is new but it is compact - I rewrote a Form app in WPF and the WPF has 1/3 the lines and more features. Read a whole book on WPF just to get grounded - I like PRO WPF in C# 2010. You could also say LINQ is complex but man does it do a lot in just a few key strokes. WPF is not something you just pick up on the fly as you next application.
We were building out the next version of an in-house thick-client application using WPF/Prism (Composite Application Library). As we were nearly done with the client our team was put under new management and shortly thereafter:
We were then directed to drop the Prism framework to keep things simple. This includes not using any type of Inversion of Control.
We were directed to build out the WPF application without using MVVM or similar; and more along the lines of a traditional WinForm application. The idea is that if a developer sees a control in Visual Studio’s designer view, then (s)he should be able to click on the control and see exactly what it's doing without having to traverse through a view-model (or similar).
We have now been tasked with building out the WPF application using one primary Window, use a Frame Control to contain the content, and use a Ribbon outside of the frame for the menu items. Reason we were provided to use Frame Control:
a. We will show a view in the Frame with a Page (not a user control) and then load the page in the Frame.
b. When a new view is to be shown in the Frame, the current view (Page) will be closed/disposed and the new view (Page) will take its place in the Frame.
c. When a developer looks at the Page in design view, (s)he will be able to click on any control and see exactly what is being done.
Given the restrictions of 1 and 2 above, we’d like to present another method of building out the application that:
Can be presented as an alternative to using the “Frame Methodology” (item 3 above) but still provides the same type of functionality.
Does not use MVVM (see #1 and #2 above).
Provided the direction we’ve been given, any suggestions as to an alternative we can present? I’d request that the responses be kept on the professional level and thank you in advance.
I'd personally try to argue to use Martin Fowler's Presentation Model. (That's a joke, btw...)
Basically, you're being given a restriction that says "Use WPF, but don't use any of the features that make WPF usable." It really sounds like your requirements are such that you would be much better off explaining, reasonably, the advantages of patterns like MVVM.
It sounds like the weird requirements are really boiling down to this:
The idea is that if a developer sees a control in Visual Studio’s designer view, then (s)he should be able to click on the control and see exactly what it's doing
If that's the main issue, and the reason you're avoiding MVVM and other similar patterns, I would seriously take the time to educate the management. Looking at a Command, by name, instead of an event, by name (which is what you see in the designer) is really no more difficult.
However, in a large scale application, the separation of concerns is key. Even a properly designed Windows Forms application requires a clean separation of concerns - but with event based programming, this becomes much more difficult, especially from the designer. If you try to develop a large scale, clean, application using an event approach, you'll have event handlers, but those event handlers will all eventually need to delegate their work to a separate component.
This is actually adding an extra level of effort, from an understandability and maintenance point of view, on top of what you get with MVVM. With MVVM, you only look to the ViewModel, which is very discoverable.
BTW - The "rationale" for using a Page instead of a UserControl doesn't make any sense. You can do exactly the same thing you're describing with UserControls... The only reason to use a Frame and Page is if you want to take advantage of navigation, in which case, you can't dispose the old pages directly (or they get regenerated constantly). Also, the navigation tools probably wouldn't be used with a ribbon - the two conceptual models are quite different.
There are criticisms of MVVM which may be applicable to your project; however having unreasonable dictates of programming methodology is always a recipe for disaster.
One of the reasons that we have frameworks and spending time building layers and separation is to avoid the coding mess that always results when you can "simply click on the button in visual studio to see the code that is being executed".
There may not be a way of achieving what you've been asked to do without something similar to MVVM, because anything that has an architecture may well be labelled as being too similar.
However I have been using a system for many years that provides simple inter-object plumbing currently called Emesary you may want to read my C# .NET Emesary walkthrough.
But basically it allows my buttons to be implemented thus:
private void addButton_Click(object sender, RoutedEventArgs e)
{
GlobalTransmitter.NotifyAll(new Notification(NotificationType.CreateRecipe));
}
This may be an answer to your problem. It's under hyped, small and so simple but it just works well.
I've achieved a solution to the second question by using a Window, a user control for the ribbon bar (the user control contains the listview), and another user control for the Frame part. This second user control obvious is built using other user controls using a very simple view class. All views and controls are connected using Emesary.
As a school project I had to develop a WPF client which allowed for multiple people to make use of it at the same time. And I used Pages. My verdict: Save yourself a huge amount of effort, and use UserControls instead.
Sometimes the Page Navigator (which you'll use to scroll through) tends to bug out and cause you a lot of problems. Maybe it was my crappy coding, but who knows?
Though I must say, the control being called "Pages" is somewhat misleading... I went "Eureka!" when I found them, and swore at them thereafter.
I totally agree with #2 (MS bigs take note!). It would be cool if you could double-click a Control and it would take you straight to its command (or event if its command is lacking). However till then, make sure that you organize your Views and ViewModels in separate folders.
Having a dual screen (or a very wide one) will allow you to have two instances of VS open on the project, one focused around the View and the other around the ViewModel (my personal choice was having Expression Blend on the View).
Although not a very big application, I managed to convert my project to proper MVVM (ie. ViewModel for every UI element, RelayCommands and Mediator) in a matter of days, so once you understand it it's not too complicated to implement. Plus, there are tools out there (such as Josh Smith's RelayCommand and Marlon Grech's Mediator - totally free, by the way) which make MVVM half as difficult, and twice as powerful.
Using WPF without MVVM is like trying to eat rice without a fork. You'd be better off using WinForms if you're not going to take advantage of what WPF has to offer. My 2 cents.
I wish I could say your management is totally wrong.. but I cannot say that as it will not be the most accurate truth. I guess that the main reason to the changes you described is either because the new manager is not comfortable with the concept of MVVM being the new messiah of UI development or/and another reason could be the cost of educated sophisticated developers vs. cheap developers which can be instructed to get the things done as fast as possible, a concept which is widely known as lean development.
So, putting all I wrote so far under "not what you asked for", here is what I suggest:
you can still use object oriented pure approach, meaning you can have a model object which already have method to show UI information. so every object will be a window derived object, that way you will loose on SOC but you still going to be OOP/OOD.
But LOL, The next phase will bring you to seperation of model from view in order to not repeat the same code in many derrived windows which relay on the same data... so your management will endorse MVC/MVP as good solution .. and the distance from it to MVVM is kinda of short if they want WPF.
Conclusion: you will have to teach your manager why it is better to go for MVVM, unless the project is very short.
Using the Composite Application Guidance tools from Microsoft, It seems as if there is no mechanism to allow you to query your modules ViewModels and ask if any of them have unsaved data. This is a problem because, and I'm guilty of this as well, you cannot stop the application from terminating when there is unsaved data...
I had thought about creating an interface called IApplicationEvents and have an event on there called ApplicationExiting. The thought being that each module can subscribe to the event and, when fired, can send back a "Cancel=true" or "Cancel=false" to say whether or not to allow the application exiting.
Curious to find out what others may have done in this instance, and to see what possible solutions there are in the community to solve this issue.
Thx.
There are a lot of choices here.
First off, I wanted to clarify a little nomenclature... typically your Views or ViewModels contained within your Module assemblies are the things with unsaved changes, not the Module itself. The Module is responsible for instantiating any views necessary at the start and contributing back to the shell during Initialize and that's typically it, so when you attack this problem, you'll want to focus on your views/viewmodels and not the Module classes.
Options off the top of my head:
Adopt a complimentary framework like Caliburn that has support for application events like this (as well as some MDI events like ViewClosing, that kind of thing). It has builtin support for Prism (http://caliburn.codeplex.com/)
Use a composite command. Your views or viewmodels will register themselves with a composite command elsewhere (CloseCommand, which you declare statically for your application) and every open view will have its CanExecute and Execute methods fired so that you can both vote in the closing of the application and also react to it, should it happen anyway. CompositeCommands are a feature of Prism. (See: Commanding Quickstart)
I think those are probably the most elegant. There's a few more options but these live in the best harmony with existing conventions.
Hope this helps.