问题
I'm working on some .Net XAML application using MVVM pattern. According to MVVM I keep my app logic in VM and in Code Behind I do UI-related actions. But I need to execute some UI-related code in Code Behind in respond to some logic in VM.
Example: I need to show an error message (custom toast notification in my case) when login operation failed. Login operation resides in VM, but I can't use any UI-specific classes in my VM, so I made an event in VM and hooking up to in in Code Behind, doing UI stuff.
Is it a violation of MVVM pattern? If yes, then how to solve my case?
回答1:
Ideally communication between View and ViewModel in MVVM pattern done through Mediator to avoid hard-referencing View from VM. Having a mediator,
- View can subscribe to certain type of message.
- Then VM send the message to mediator,
- mediator broadcast the message, so all party that subscribed will get it.
- Upon receiving, View can respond by executing certain UI logic according to the message
The CodeProject link above shows how to implement a mediator class. But I will suggest to use a popular MVVM framework since you'll find it has Mediator implementation and many other tools for MVVM available out-of-the-box.
来源：https://stackoverflow.com/questions/21330409/mvvm-calling-ui-logic-in-code-behind-from-viewmodel