Why is mvvm good

This makes the binding from View to ViewModel via Commands much cleaner. I'm currently using Postsharp, though I believe there are other tools that can do this. If I hadn't discovered this, I probably would've given up by now, as the boilerplate code to implement it manually was really bugging me.

I've had to invert my approach to how the software is implemented. Instead of having a dictator class that tells all of its minions what to do, which in turn use their minions, my software becomes more a matter of loosely coupled services that say:. When you begin to structure your code in this way and use tools that make it easy to wire up the dependencies there are a wide range of IoC frameworks to choose from , I've found it eases some of the awkwardness of MVVM, as you can reduce the boilerplate code associated with injecting the Models into the ViewModels and locating various View Services such as displaying file dialogs for your ViewModels to consume.

It's a huge investment to learn this different approach and, as with any major shift in implementation, productivity is much lower when you first start using it. However, I'm beginning to see some light at the end of the tunnel and I believe that, once I've mastered the messy details, my applications will be cleaner and much more maintainable. I've customized it a bit for my use, but that gives you the gist of it. With this, I just tag the class [NotifyPropertyChanged] and all of the public properties will have the pattern implemented in their setters even if they are auto-property setters.

It feels much cleaner to me, as I no longer have to worry about whether I want to take the time to make the class implement INotifyPropertyChanged. I can just add the attribute and be done with it.

I agree that using MVVM put more weight on our shoulders by writing ore code, but look at the bright side where everything is isolated then if you are a designer so you can design your program and other can code it for you and other does the Database layer for you,look how maintainable enviroment you will be in especially in large enterprise applications if you would not use MVVM ,then the maintainance is almost killing I myself used it when developing ERP solution now the maintainance is pretty straight forward because of that isolation level.

You'll be happy in the long run if you use a pattern like MVVM for all the reasons the others have posted. Remember, you don't need to follow the pattern requirements word-for-word, just make sure you have good separation between your window View and your logic code-behind.

It's just Seperation of concerns not more. You could also write the ViewModel logic into the Controller. The ViewModel is just repsonsible for doing a conversion for example and object into a string. By using MVVM you use more object-oriented programming style. By writing the conversion logic into the Controller you use more functional programming style. So it comes down to having more code with better readability or less code with big Controller files.

I have no idea why there's a wide consensus to leave the C. How are we doing? Please help us improve Stack Overflow. Take our short survey. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams?

Collectives on Stack Overflow. Learn more. Why use MVVM? Ask Question. Asked 11 years, 7 months ago. Active 2 years, 2 months ago. Viewed 36k times. Or at least hard to find Cannot think of a single scenario where this is advantageous. Improve this question. Community Bot 1 1 1 silver badge. Michal Ciechan Michal Ciechan If you have evaluated it several times and you haven't seen advantages in using it, don't use it. Why use multiple question marks?

It seems to be a duplicate of quite some questions that show up as related: stackoverflow. Daniel I know but I want some example scenarios to hopefully change my mind and actually implement it! MVVM just makes things simpler and testable. This could answer some of the questions: wintellect.

I'm posting as a comment because it's just a link, not a real answer. Show 1 more comment. Active Oldest Votes. Summary The usage of all patterns is situational, and the benefit if there is any always lies in reduced complexity. ViewModel projects the data from the Model into a format that fits the View. For trivial projects MVVM is unnecessary. Using only the View is sufficient. Model and ViewModel do not need to exist from the start and can be introduced when they are needed.

When to use patterns and when to avoid them For a sufficiently simple application every design pattern is overkill. To explain familiar and unfamiliar complexity, take the following 2 sequences of characters: "D. Introducing the ViewModel There is no ViewModel in the application because until now the Model presents the data in exactly the way the Csv needs it, which is also the way the View needed it.

New requirements: different way to format the data The next customer request is that we should not display the data as rows in a table, but instead display the information of each item a.

New requirements: dynamic exchange rate The next customer request is that we pull the exchange rate from the internet, rather than using a predefined exchange rate. Improve this answer. Peter Peter 5, 1 1 gold badge 22 22 silver badges 41 41 bronze badges. Peter Brilliant explanation! This is a very very well written article! Very helpful! Hey Peter, grate explanation. I have one question though. For the case of " New Requirements: Show price in Euro " you have mentioned above, can you explain maybe a code snippet or something to understand how viewmodel is handling this.

Is it like, new data model class is created having the new column as a property and use this model for binding to the view? Add a comment. Paul Sasik Paul Sasik Thats why I asked this question. It has happened to me before. I just need some motivation to stop being lazy and write some extra in my opinion duplicate code — Michal Ciechan. Could you give a real-life example of a feature that would take a long time to implement and using MVVM it would of been easy. For example, you can make Enum values appear much more user-friendly in the UI by converting the actual Enum value to a user-friendly string maybe even localized.

Or do you want your users to read values like "VeryHigh", "LightRed",? Thanks, i have now decided to go with MVVM. In an old school Winforms app you'd have a massive headache to support two UIs simultaneously.

The separation gammelgul speaks of would have helped significantly. For example, a date might be stored on the model as number of seconds since midnight on January 1, Unix Time. To the end user, however, it is presented with the month name, date, and year in their local time zone.

A view can also have behaviors associated with it, such as accepting user input. The view manages input key presses, mouse movements, touch gestures, etc which ultimately manipulates properties of the model. In MVVM, the view is active. One thing to remember about the view is that it is not responsible for maintaining its state.

Instead, it will synchronize this with the viewmodel. The viewmodel is a key piece of the triad because it introduces Presentation Separation , or the concept of keeping the nuances of the view separate from the model.

The controller might take input from the view and place it on the model, or it might interact with a service to retrieve the model, then translate properties and place it on the view. The viewmodel also exposes methods, commands, and other points that help maintain the state of the view, manipulate the model as the result of actions on the view, and trigger events in the view itself. The examples of the pattern often focus on XAML for the view definition and data-binding for commands and properties.

These are more implementation details of the pattern rather than intrinsic to the pattern itself, which is why I offset data-binding with a different color:. Here is what a sample view model might look like. This view model is obviously designed to manage a list of contacts. It also exposes a delete command and a flag to indicate whether delete is allowed thus maintaining state for the view. The view model here makes a concrete reference to the service, you would most likely wire in that reference externally or use a dependency injection framework.

The phone numbers, of course, are faked. These mechanisms help implement the pattern by binding UI behaviors to the underlying models. In Silverlight, the VSM should be the primary choice for coordination of transitions and animations. Learn more about VSM. The viewmodel becomes wholly responsible for the model in this scenario. You might have heard discussion about view first or viewmodel first. In general, I believe most developers agree that a view should have exactly one viewmodel. There is no need to attach multiple viewmodels to a single view.

A view may be composed of other views, each with its own viewmodel. Viewmodels might compose other viewmodels when necessary often, however, I see people composing and aggregating viewmodels when in fact what they really want is messaging between viewmodels. While a view should only have one viewmodel, a single viewmodel might be used by multiple views imagine a wizard, for example, that has three views but all bind to the same viewmodel that drives the process. View first simply means the view is what drives the creation or discovery of the view model.

In view first scenarios, the view typically binds to the view model as a resource, uses a locator pattern, or has the view model injected via MEF, Unity, or some other means. This is a very common method for managing views and view models. Here are some of my posts on the topic:. The view is created, then the view model attached. In the App object, it looks like this:. ViewModel first is another method to wire the framework together.

In this scenario, the viewmodel is responsible for creating the view and binding itself to the view. The second issue exists in Silverlight 3 because the ICommand interface is provided, but not implemented. These are implementation details that make it easier to use the MVVM pattern. I also implemented a command. Typically you would have a more generic type of command to handle different situations, but again, for the sake of illustration, I simply created a delete command specific to the function it performs.

I am using a message box to confirm the delete. If you require something more elegant like a ChildWindow , read the scenarios I describe below to better understand how to integrate a dialog box as a service within MVVM.

This particular command uses a delegate to callback when it is done, but this would only allow for a single subscriber. A multicast delegate or event will be required if multiple consumers or viewmodels for the command exist. In Silverlight 4, I can simply bind a button to the command using the Command tag. I built the example in Silverlight 3, which does not have native support. To create the binding, I made a simple trigger — again, specific to this project and for the sake of illustration — to invoke the command, so I can easily bind it in the XAML.

You can also delete a contact. I often receive complaints that blog examples are too simple. You can download the source code for this example here. You can also see it in action here click on the names and try delete … I simulated a slight delay for the initial load and the refresh after a delete.

You may or may not want to do this in practice. Having the configure code separately for each view may be simpler in that case. MVVM works well if your app requires many model-to-view transformations. However, not every object will neatly fit into the categories of model, view or view model. Instead, you should use MVVM in combination with other design patterns.

Furthermore, MVVM may not be very useful when you first create your application. MVC may be a better starting point. This app displays nearby coffee shops provided by Yelp.

Everything you need has been included for you in the starter project. The only thing you need to remember is to open CoffeeQuest. Open APIKeys. These map pins are kind of boring. Open MapPin. MapPin takes a coordinate , title , and rating , then converts those into something a map view can display… does this sound familiar? First, you need to give this class a better name. This will rename both the class name and file name in the File hierarchy.

Next, select the Models group in the File hierarchy and press Enter to edit its name. Rename this to ViewModels. Finally, click on the yellow CoffeeQuest group and select Sort by name. Ultimately, your File hierarchy should look like this:.

BusinessMapViewModel needs a few more properties in order to show exciting map annotations, instead of the plain-vanilla pins provided by MapKit.

Still inside BusinessMapViewModel , add the following properties after the existing ones; ignore the resulting compiler errors for now:. You accept image via this initializer and set ratingDescription from the rating. This tells the map to use ratingDescription as the subtitle shown on annotation callout when one is selected.

Now you can fix the compiler error. Open ViewController. High-quality caffeine is like catnip for developers, so you label anything less than 3. You gotta have high standards, right? Build and run, and you should see the custom images! It appears most San Francisco coffee shops are actually 4 stars or above, and you can find the very best shops at a glance. You learned about the MVVM pattern in this chapter.