[英]How to use a ViewModelLocator in a user control?
I was asked to convert a standalone WPF application that uses the MVVM pattern into a user control. 我被要求将使用MVVM模式的独立WPF应用程序转换为用户控件。 This app consists of a main window and a few other windows.
这个应用程序包含一个主窗口和一些其他窗口。 However, I get a few errors when trying to do so all pointing to my App.xaml class and other resources declared like converters:
但是,尝试这样做时会遇到一些错误,这些错误都指向我的App.xaml类和声明为转换器的其他资源:
Library project file cannot specify ApplicationDefintion element.
The project file contains a property value that is not valid.
The name "ViewModelLocator" does not exist in the namespace "clr-namespace:MapperX.ViewModels"
. The name "ViewModelLocator" does not exist in the namespace "clr-namespace:MapperX.ViewModels"
。
So it looks like the errors revolve around my ViewModelLocator. 因此,看来错误围绕着我的ViewModelLocator。
Currently the project directory structure is set up like so: 当前,项目目录结构的设置如下:
Top level -> ViewModels folder -> ViewModelLocator 顶层-> ViewModels文件夹-> ViewModelLocator
The App.xaml is set up like so: App.xaml的设置如下:
<Application x:Class="MapperX.App"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="clr-namespace:MapperX"
xmlns:vm="clr-namespace:MapperX.ViewModels"
StartupUri="MainWindow.xaml">
<Application.Resources>
<vm:ViewModelLocator x:Key="ViewModelLocator" />
</Application.Resources>
</Application>
And here's a snippet of the ViewModelLocator
class: 这是
ViewModelLocator
类的片段:
namespace MapperX.ViewModels
{
/// <summary>
/// This class instantiates all the viewmodels
/// </summary>
public class ViewModelLocator
{
WpfMap map = new WpfMap();
private MainViewModel _mainViewModel;
public MainViewModel MainViewModel
{
get
{
if (_mainViewModel == null)
{
_mainViewModel = new MainViewModel(map)
}
return _mainViewModel;
}
}
private LayersViewModel _layersViewModel;
public LayersViewModel LayersViewModel
{
get
{
if (_layersViewModel == null)
{
_layersViewModel = new LayersViewModel(map)
}
return _layersViewModel;
}
}
}
}
And then I set the DataContext
for the views .xaml like so: DataContext="{Binding Path=MainViewModel, Source={StaticResource ViewModelLocator}}"
然后像这样设置视图.xaml的
DataContext
: DataContext="{Binding Path=MainViewModel, Source={StaticResource ViewModelLocator}}"
What's the correct way to still be able to use the ViewModelLocator without the App.xaml?? 在没有App.xaml的情况下仍然能够使用ViewModelLocator的正确方法是什么?
Why not put the ViewModelLocator
in your top-level UserControl
? 为什么不将
ViewModelLocator
放在顶级UserControl
?
<UserControl.Resources>
<vm:ViewModelLocator x:Key="ViewModelLocator" />
</UserControl.Resources>
Instead of relying on a resource, you may create an attached property to set the DataContext
of the views in your control library: 您可以创建一个附加属性来设置控件库中视图的
DataContext
,而不是依赖资源:
namespace ControlsAndResources
{
public class View
{
private static readonly ViewModelLocator s_viewModelLocator = new ViewModelLocator();
public static readonly DependencyProperty ViewModelProperty = DependencyProperty.RegisterAttached("ViewModel", typeof(string),
typeof(ViewModelLocator), new PropertyMetadata(new PropertyChangedCallback(OnChanged)));
public static void SetViewModel(UserControl view, string value) => view.SetValue(ViewModelProperty, value);
public static string GetViewModel(UserControl view) => (string)view.GetValue(ViewModelProperty);
private static void OnChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
UserControl view = (UserControl)d;
string viewModel = e.NewValue as string;
switch (viewModel)
{
case "MainViewModel":
view.DataContext = s_viewModelLocator.MainViewModel;
break;
case "LayersViewModel":
view.DataContext = s_viewModelLocator.LayersViewModel;
break;
default:
view.DataContext = null;
break;
}
}
}
}
Usage: 用法:
<UserControl xmlns:local="clr-namespace:ControlsAndResources" ...
local:View.ViewModel="MainViewModel">
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