选择选项卡时获取它的视图模型的属性 [英] Get a property of a tabitem's viewmodel when it's selected

问题描述

我有一个 UserControl ParentView 包含一个 DataGrid 和一个 catel:TabControl，其中每个 TabItem 是一个很小的 ​​UserControl，它的 ViewModel 是 BaseTabViewModel 的 子类.

I have a UserControl ParentView containing a DataGrid and a catel:TabControl, in which each TabItem is a tiny UserControl and whose ViewModel is a subclass of a BaseTabViewModel.

此BaseTabViewModel 包含一个自定义类的ObservableCollection，其属性将生成DataGrid 的列.

This BaseTabViewModel contains a ObservableCollection of a custom class, whose properties will generate the columns of the DataGrid.

由于所有选项卡只有一个 DataGrid，我如何使用所选选项卡的视图模型的 ObservableCollection 自动填充它?

现在，我只是卸载选项卡 (LoadTabItems="SingleUnloadOthers")，并且由于每个选项卡的视图模型在实例化时都会重新生成其集合，因此我使用了 InterestedIn 和 OnViewModelPropertyChanged 来获取它；但是这种卸载行为并不完全可靠，我经常发现自己的 DataGrid 仍然由前一个选项卡填充，而不是在更改选项卡时被清除.

Right now, I just unload tabs (LoadTabItems="SingleUnloadOthers") and, since every tab's viewmodel regenerate its collection when instanciated, I use InterestedIn and OnViewModelPropertyChanged to get it; yet this unloading behavior isn't completely reliable, and I often find myself with the DataGrid still filled by the previous tab instead of being cleaned when changing tab.

需要注意的是，它被清理并不是一种理想的行为，我现在别无选择.让每个标签保持加载状态是我的目标.

To note, the fact that it gets cleaned isn't a desired behavior, I just have no other choice right now. Having each tab remaining loaded is my goal.

我知道当涉及到视图模型时，继承是很不受欢迎的，但老实说，我想不出更好的方法来做到这一点.

父视图

<Grid>
    <Grid.RowDefinitions>
        <RowDefinition Height="Auto"/>
        <RowDefinition/>
    </Grid.RowDefinitions>
    <catel:TabControl LoadTabItems="SingleUnloadOthers">
        <TabItem Header="FIRST">
            <local:FirstView/>
        </TabItem>
        <TabItem Header="SECOND">
            <local:SecondView/>
        </TabItem>
        <TabItem Header="THIRD">
            <local:ThirdView/>
        </TabItem>
        <TabItem Header="FOURTH">
            <local:FourthView/>
        </TabItem>
    </catel:TabControl>

    <DataGrid Grid.Row="1" IsReadOnly="True" ItemsSource="{Binding Fields}"/>
</Grid>

父视图模型

[InterestedIn(typeof(FirstViewModel))]
[InterestedIn(typeof(SecondViewModel))]
[InterestedIn(typeof(ThirdViewModel))]
[InterestedIn(typeof(FourthViewModel))]
public class ParentViewModel : ViewModelBase
{
    public ObservableCollection<Field> Fields
    {
        get { return GetValue<ObservableCollection<Field>>(FieldsProperty); }
        set { SetValue(FieldsProperty, value); }
    }
    public static readonly PropertyData FieldsProperty = RegisterProperty("Fields", typeof(ObservableCollection<Field>));

    protected override void OnViewModelPropertyChanged(IViewModel viewModel, string propertyName)
    {
        if (propertyName.Equals("Fields"))
        {
            BaseParserViewModel p = viewModel as BaseParserViewModel;
            Fields = p != null ?? p.Fields;
        }
        base.OnViewModelPropertyChanged(viewModel, propertyName);
    }
}

BaseTabViewModel

public abstract class BaseTabViewModel : ViewModelBase
{
    protected BaseParserViewModel()
    {
        Fields = new ObservableCollection<Field>();
    }

    public ObservableCollection<Field> Fields
    {
        get { return GetValue<ObservableCollection<Field>>(FieldsProperty); }
        set { SetValue(FieldsProperty, value); }

    public static readonly PropertyData FieldsProperty = RegisterProperty("Fields", typeof(ObservableCollection<MappedField>));

}

BaseTabViewModel 的子项没有任何兴趣，因为除了某些 [ViewModelToModel] 属性之外，它们不与父项交互.

BaseTabViewModel's childs have nothing of interest, as they don't interact with their parent, except for some [ViewModelToModel] properties.

推荐答案

如果你需要跨多个视图模型管理状态，我总是建议引入一个服务.视图模型可以存活很短或很长一段时间，但视图模型之间最好的通信仍然是保持状态的服务(即使虚拟机已经消失).

If you need to manage state across several view models, I always recommend introducing a service. A view model is something that can live for a short or long amount of time, but the best communication between view models is still services that hold the state (even when the vm's are gone).

以下是我的交流偏好:

1. 服务(最佳方式，允许完全控制，最佳性能)
2. 基于属性的通信
3. 消息传递(MessageMediator)

我知道很多人都用 3 解决了他们的架构问题，但这是一个黑客，而不是一个可靠的解决方案.只需实现一个服务(注入所有虚拟机)，如下所示:

I know a lot of people fix their architectural issues with 3, but it's a hack, not a solid solution. Just implement a service (that gets injected into all vm's) like this:

public class FieldCollectionManagementService : IFieldCollectionManagementService
{
    private ObservableCollection<Field> _selectedCollection;

    public ObservableCollection<Field> SelectedCollection
    {
        get { return _selectedCollection; }
        set
        {
            _selectedCollection = value;
            SelectedCollectionChanged.SafeInvoke(this);
        }
    }

    public event EventHandler<EventArgs> SelectedCollectionChanged;
}

现在您无需属性即可轻松处理所有更改.然后你甚至可以在所有视图模型都消失后恢复状态.

Now you can easily handle all the changes without needing the attributes. Then you can even restore state when all view models are gone.

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