为改变一个ViewModel查看 [英] Changing the View for a ViewModel

问题描述

我试图实施吨WPF应用程序的设计MVVM百通。为了将视图连接到的ViewModels，我用的，这看起来 ResourceDictionary中（以 Application.Resources 使用）像

I am trying to implement the MVVM design patern for mt WPF application. In order to connect the view to the viewmodels, I use a ResourceDictionary (used in Application.Resources), that looks like

<DataTemplate DataType={x:Type viewmodel:SampleViewModel}>
    <view:SampleView1 />
</DataTemplate>

视图模型，然后简单地投入内容presenters显示它们。

The view models are then simply put into content presenters to display them.

现在，当用户presses一个按钮，我想使用不同的视图来显示 SampleViewModel 。如何更改用于 SampleViewModel ？

Now, when the user presses a button, I'd like to display SampleViewModel using a different view. How do I change the data template used for SampleViewModel?

推荐答案

少言多code。
如你所说至于，你有类 SampleViewModel 。我加了属性标题示范和 ViewType 确定正确的观点：

Less words more code. As far as you said, you have the class SampleViewModel. I added the property Title for demonstration and ViewType for identifying the correct view:

public enum ItemViewType { View1, View2 };

public class SampleViewModel 
{
    public string Title { get; set; }
    public ItemViewType ViewType { get; set; }
}

的 DataTemplateSelector 为视 ViewType 属性两种观点：

class ItemViewTemplateSelector : DataTemplateSelector
{
    public DataTemplate View1Template { get; set; }
    public DataTemplate View2Template { get; set; }

    public override DataTemplate SelectTemplate(object item, DependencyObject container)
    {
        var vm = item as SampleViewModel;
        if (vm == null)
            return null;

        switch (vm.ViewType)
        {
            case ItemViewType.View1:
                return View1Template;
            case ItemViewType.View2:
                return View2Template;
        }

        return null;
    }
}

XAML中code：

Xaml code:

<Window.Resources>
    <DataTemplate x:Key="view1Template">
        <TextBlock Text="{Binding Title}" Foreground="Red"/>
    </DataTemplate>
    <DataTemplate x:Key="view2Template">
        <TextBox Text="{Binding Title}" />
    </DataTemplate>
    <local:ItemViewTemplateSelector x:Key="viewTemplateSelector"
                                    View1Template="{StaticResource view1Template}"
                                    View2Template="{StaticResource view2Template}"/>
</Window.Resources>

<Window.DataContext>
    <local:MainViewModel/>
</Window.DataContext>

<StackPanel>
    <Button Content="ChangeView" HorizontalAlignment="Center" Command="{Binding SwitchViewCommand}"/>
    <ContentControl  Content="{Binding ItemViewModel}" ContentTemplateSelector="{StaticResource viewTemplateSelector}"/>
</StackPanel>

的主要部分是在类 MainViewModel ，我已经把逻辑切换视图：

The main part is in the class MainViewModel where I've put the logic for switching views:

public class MainViewModel : ViewModelBase
{
    public MainViewModel()
    {
        this.ItemViewModel = new SampleViewModel { Title = "Some title", ViewType = ItemViewType.View1 };

        this.SwitchViewCommand = new RelayCommand(() =>
        {
            this.ItemViewModel.ViewType = this.ItemViewModel.ViewType == ItemViewType.View1
                                            ? ItemViewType.View2
                                            : ItemViewType.View1;
            //The magic senquence of actions which forces a contentcontrol to change the content template
            var copy = this.ItemViewModel;
            this.ItemViewModel = null;
            this.ItemViewModel = copy;
        });
    }

    public RelayCommand SwitchViewCommand { get; set; }

    private SampleViewModel itemViewModel;

    public SampleViewModel ItemViewModel
    {
        get { return itemViewModel; }
        set
        {
            itemViewModel = value;
            RaisePropertyChanged("ItemViewModel");
        }
    }
}

的 SwitchViewCommand 可以是任何类型的命令，我用命令从mvvmlight库。

The SwitchViewCommand can be any type of command, I use the command from the mvvmlight library.

命令的处理函数中更改视图模型的类型和一个取巧的方法更新属性 ItemViewModel ，因为 ContentControl中刷新仅当更改内容属性来看，除非你设置为不同的对象的引用此属性不会改变。

Inside the handler of the command I change the type of viewmodel and update the property ItemViewModel in a tricky way because a ContentControl refreshes a view only if to change the Content property, and this property will not be changed unless you set a reference to different object.

我的意思是，即使是code this.ItemViewModel = this.itemViewModel 不会改变的观点。
很奇怪，但解决方法并不需要太多的工作。

I mean, even the code this.ItemViewModel = this.itemViewModel will not change the view. It's strange, but the workaround doesn't require much work.

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