Prism/mef ViewModel：财产相对于 ctor 的优点和缺点
在 StockTraderRI 示例代码中，MEF 使用属性注入 ViewModel：
[Export(typeof(IOrdersView))]
[PartCreationPolicy(CreationPolicy.NonShared)]
public partial class OrdersView : UserControl, IOrdersView
{
public OrdersView()
{
InitializeComponent();
}
[Import]
[SuppressMessage("Microsoft.Design", "CA1044:PropertiesShouldNotBeWriteOnly", Justification = "Needs to be a property to be composed by MEF")]
public IOrdersViewModel ViewModel
{
set { this.DataContext = value; }
}
}
我想知道的是： 为什么不使用像这样的 ImportingConstructor 来注入 ViewModel：
[Export(typeof(IOrdersView))]
[PartCreationPolicy(CreationPolicy.NonShared)]
public partial class OrdersView : UserControl, IOrdersView
{
[ImportingConstructor]
public OrdersView(IOrdersViewModel ViewModel)
{
InitializeComponent();
this.DataContext = ViewModel;
}
}
是否有特殊功能、问题或原因 我想念为什么 StockTraderRI 示例确实使用属性而不是 ctor 的参数？
In the StockTraderRI sample code the ViewModel is injected by MEF using a property:
[Export(typeof(IOrdersView))]
[PartCreationPolicy(CreationPolicy.NonShared)]
public partial class OrdersView : UserControl, IOrdersView
{
public OrdersView()
{
InitializeComponent();
}
[Import]
[SuppressMessage("Microsoft.Design", "CA1044:PropertiesShouldNotBeWriteOnly", Justification = "Needs to be a property to be composed by MEF")]
public IOrdersViewModel ViewModel
{
set { this.DataContext = value; }
}
}
What I wonder is: why not use an ImportingConstructor like this to inject the ViewModel:
[Export(typeof(IOrdersView))]
[PartCreationPolicy(CreationPolicy.NonShared)]
public partial class OrdersView : UserControl, IOrdersView
{
[ImportingConstructor]
public OrdersView(IOrdersViewModel ViewModel)
{
InitializeComponent();
this.DataContext = ViewModel;
}
}
Is there a special feature, problem or reason I miss why the StockTraderRI sample does use a Property instead of a paramter to the ctor?
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因为在 XAML 中部分定义的类型不能很好地与参数化构造函数配合使用。 XAML 构建在“创建空白对象并随后填充属性”范例之上。
Because types partially defined in XAML don't play well with parametrized constructors. XAML is built on the "create a blank object and fill in the properties afterwards" paradigm.