WPF MVVM视图模型构造的designMode
问题描述:
我有一个主要的WPF窗口:
I've got a main wpf window:
<Window x:Class="NorthwindInterface.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:ViewModels="clr-namespace:NorthwindInterface.ViewModels" Title="MainWindow" Height="350" Width="525">
<Window.DataContext>
<ViewModels:MainViewModel />
</Window.DataContext>
<ListView ItemsSource="{Binding Path=Customers}">
</ListView>
</Window>
而MainViewModel是这样的:
And the MainViewModel is this:
class MainViewModel : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged = delegate { };
public MainViewModel()
{
Console.WriteLine("test");
using (NorthwindEntities northwindEntities = new NorthwindEntities())
{
this.Customers = (from c in northwindEntities.Customers
select c).ToList();
}
}
public List<Customer> Customers { get;private set; }
现在的问题是,在designermode我看不到我的MainViewModel,它强调它说,它不能创建MainViewModel的一个实例。它连接到数据库。这就是为什么(当我评论了code中的问题解决)。
Now the problem is that in designermode I can't see my MainViewModel, it highlights it saying that it can't create an instance of the MainViewModel. It is connecting to a database. That is why (when I comment the code the problem is solved).
但我不希望出现这种情况。解决这个最佳做法的任何解决方案?
But I don't want that. Any solutions on best practices around this?
和为什么这项工作MVVM工作时:
And why does this work when working with MVVM:
/// <summary>
/// Initializes a new instance of the <see cref="MainViewModel"/> class.
/// </summary>
public MainViewModel()
{
// Just providing a default Uri to use here...
this.Uri = new Uri("http://www.microsoft.com/feeds/msdn/en-us/rss.xml");
this.LoadFeedCommand = new ActionCommand(() => this.Feed = Feed.Read(this.Uri), () => true);
this.LoadFeedCommand.Execute(null); // Provide default set of behavior
}
甚至完全执行在设计时。
It even executes perfectly at design time.
答
这将让你看到设计师。
public MainViewModel()
{
if (!DesignerProperties.IsInDesignTool)
{
Console.WriteLine("test");
using (NorthwindEntities northwindEntities = new NorthwindEntities())
{
this.Customers = (from c in northwindEntities.Customers
select c).ToList();
}
}
}