Handling Dialogs in WPF with MVVM

 

In the MVVM pattern for WPF, handling dialogs is one of the more complex operations. As your view model does not know anything about the view, dialog communication can be interesting. I can expose an ICommand that when the view invokes it, a dialog can appear.

Does anyone know of a good way to handle results from dialogs? I am speaking about windows dialogs such as MessageBox.

One of the ways we did this was have an event on the viewmodel that the view would subscribe to when a dialog was required. 

public event EventHandler<MyDeleteArgs> RequiresDeleteDialog;

This is OK, but it means that the view requires code which is something I would like to stay away from.

I suggest forgoing the 1990's modal dialogs and instead implementing a control as an overlay (canvas+absolute positioning) with visibility tied to a boolean back in the VM. Closer to an ajax type control.

This is very useful: 

<BooleanToVisibilityConverter x:Key="booltoVis" />

as in: 

<my:ErrorControl Visibility="{Binding Path=ThereWasAnError, Mode=TwoWay, Converter={StaticResource booltoVis}, UpdateSourceTrigger=PropertyChanged}"/>

Here's how I have one implemented as a user control. Clicking on the 'x' closes the control in a line of code in the usercontrol's code behind. (Since I have my Views in an .exe and ViewModels in a dll, I don't feel bad about code that manipulates UI.)

Wpf对话框

You should use a mediator for this. Mediator is a common design pattern also known as Messenger in some of its implementations. It's a paradigm of type Register/Notify and enables your ViewModel and Views to communicate through a low-coupled messaging mecanism.

You should check out the google WPF Disciples group, and just search for Mediator. You will be much happy with the answers...

You can however start with this:

http://joshsmithonwpf.wordpress.com/2009/04/06/a-mediator-prototype-for-wpf-apps/

Enjoy !

Edit: you can see the answer to this problem with the MVVM Light Toolkit here:

http://mvvmlight.codeplex.com/Thread/View.aspx?ThreadId=209338

A good MVVM dialog should:

  • Be declared with only XAML.
  • Get all of it's behavior from databinding.

    • Unfortunately, WPF doesn't provide these features. Showing a dialog requires a code-behind call to ShowDialog(). The Window class, which supports dialogs, can't be declared in XAML so it can't easily be databound to the DataContext.

    To solve this, I wrote a XAML stub control that sits in the logical tree and relays databinding to a Window and handles showing and hiding the dialog. You can find it here: http://www.codeproject.com/KB/WPF/XAMLDialog.aspx

    It's really simply to use and doesn't require any strange changs to your ViewModel and doesn't require events or messages. The basic call looks like this: 

    <dialog:Dialog Content="{Binding Path=DialogViewModel}" Showing="True" />

    You probably want to add a style that sets Showing. I explain it in my article. I hope this helps you.

    链接地址: http://www.djcxy.com/p/9592.html

    上一篇: 评估MVVM命令的“可执行”状态

    下一篇: 使用MVVM处理WPF中的对话框