WPF: switching UserControls depending on corresponding ViewModels (MVVM)
I'll try to simplify the task I'm working on by imagining this example:
Let's suppose that we have the following hierarchy of model classes:
Animal
Lion
Snake
Bird
...corresponding ViewModels:
AnimalCollectionViewModel
AnimalViewModel
LionViewModel
SnakeViewModel
BirdViewModel
... and corresponding views:
AnimalCollectionView
LionView
SnakeView
BirdView
It's supposed that AnimalCollection contains a list filled with objects of different types of animals and below the list it has a property grid for setting the properties of a selected animal. Obviously the pr开发者_如何学运维operty grids will have different properties and should change when the type of a selected item changes.
The question is: How to implement switching of the property grids in WPF according to the MVVM pattern? Using what mechanism?
Currently I have an abstract enum property in the base ViewModel (AnimalViewModel.PropertyGridType = {Lion, Snake, Bird}) which the derived classes implement by returning corresponding values. And the AnimalCollectionView changes the property grid user controls depending on the value of this property. Something like this:
...
<UserControl.Resources>
<Style x:Key="PropertyGridStyle" TargetType="ContentControl">
<Style.Triggers>
<DataTrigger Binding="{Binding PropertyGridType}" Value="Lion">
<Setter Property="Content">
<Setter.Value>
<view:LionPropertyGridView />
</Setter.Value>
</Setter>
</DataTrigger>
<DataTrigger Binding="{Binding PropertyGridType}" Value="Snake">
<Setter Property="Content">
<Setter.Value>
<view:SnakePropertyGridView />
</Setter.Value>
</Setter>
</DataTrigger>
</Style.Triggers>
</Style>
</UserControl.Resources>
<ContentControl Style="{StaticResource PropertyGridStyle}" />
...
But I'm not sure whether it is the right approach. (At least I don't like introducing the auxiliary enum property. Is it possible to deduce the necessary user control based on a ViewModel type?) Can anybody advise other options? Thanks in advance!
Is it possible to deduce the necessary user control based on a ViewModel type?
You mean, like this?
<Window.Resources>
<DataTemplate DataType="{x:Type vm:LionViewModel}">
<v:LionView />
</DataTemplate>
<DataTemplate DataType="{x:Type vm:SnakeViewModel}">
<v:SnakeView />
</DataTemplate>
<DataTemplate DataType="{x:Type vm:BirdViewModel}">
<v:BirdView/>
</DataTemplate>
</Window.Resources>
See "Applying a View to a View Model" in Josh Smith's article on MVVM.
Edit:
Here's a trivial example of type-based template selection that you can paste into Kaxaml to prove to yourself that it really works:
<Page
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:sys="clr-namespace:System;assembly=mscorlib">
<Page.Resources>
<sys:String x:Key="string">this is a string</sys:String>
<sys:Int32 x:Key="int32">1234</sys:Int32>
<DataTemplate DataType="{x:Type sys:String}">
<TextBlock Foreground="Red" Text="{Binding}"/>
</DataTemplate>
<DataTemplate DataType="{x:Type sys:Int32}">
<TextBlock Foreground="Blue" Text="{Binding}"/>
</DataTemplate>
</Page.Resources>
<StackPanel>
<ContentControl Content="{Binding Source={StaticResource string}}"/>
<ContentControl Content="{Binding Source={StaticResource int32}}"/>
</StackPanel>
</Page>
You can use DataTemplateSelector for that. The method of choosing the right template is up to you. You can use enums or test for class type if you wish.
精彩评论