双向绑定视图的 DependencyProperty 到视图模型的属性? [英] Twoway-bind view's DependencyProperty to viewmodel's property?

问题描述

网络上的多个来源告诉我们，在 MVVM 中，视图和视图模型之间的通信/同步应该通过依赖属性发生.如果我理解正确，应该使用双向绑定将视图的依赖属性绑定到视图模型的属性.现在，以前也有人问过类似的问题，但没有足够的答案.

Multiple sources on the net tells us that, in MVVM, communication/synchronization between views and viewmodels should happen through dependency properties. If I understand this correctly, a dependency property of the view should be bound to a property of the viewmodel using two-way binding. Now, similar questions have been asked before, but with no sufficient answer.

在我开始分析这个相当复杂的问题之前，我的问题是:

Before I start analyzing this rather complex problem, here's my question:

如何将自定义视图的DependencyProperty与视图模型的属性同步?

How do I synchronize a custom view's DependencyProperty with a property of the viewmodel?

在理想的世界中，您只需将其绑定如下:

In an ideal world, you would simply bind it as this:

<UserControl x:Class="MyModule.MyView" MyProperty="{Binding MyProperty}">

这不起作用，因为 MyProperty 不是 UserControl 的成员.呸！我尝试了不同的方法，但都没有成功.

That does not work since MyProperty is not a member of UserControl. Doh! I have tried different approaches, but none proved successful.

一种解决方案是定义一个基类 UserControlEx，它具有必要的依赖属性以使上述工作正常进行.但是，这很快就会变得非常混乱.不够好！

One solution is to define a base-class, UserControlEx, with necessary dependency properties to get the above to work. However, this soon becomes extremely messy. Not good enough!

推荐答案

我使用 Caliburn.Micro 将 ViewModel 与 View 分开.尽管如此，它可能在 MVVM 中以相同的方式工作.我猜 MVVM 也将视图的 DataContext 属性设置为 ViewModel 的实例.

I use Caliburn.Micro for separating the ViewModel from the View. Still, it might work the same way in MVVM. I guess MVVM sets the view's DataContext property to the instance of the ViewModel, either.

// in the class of the view: MyView
public string ViewModelString // the property which stays in sync with VM's property
{
    get { return (string)GetValue(ViewModelStringProperty); }
    set
    {
        var oldValue = (string) GetValue(ViewModelStringProperty);
        if (oldValue != value) SetValue(ViewModelStringProperty, value);
    }
}

public static readonly DependencyProperty ViewModelStringProperty =
    DependencyProperty.Register(
        "ViewModelString",
        typeof(string),
        typeof(MyView),
        new PropertyMetadata(OnStringValueChanged)
        );

private static void OnStringValueChanged(DependencyObject o, DependencyPropertyChangedEventArgs e)
{
    // do some custom stuff, if needed
    // if not, just pass null instead of a delegate
}    

public MyView()
{
    InitializeComponent();
    // This is the binding, which binds the property of the VM
    // to your dep. property.
    // My convention is give my property wrapper in the view the same
    // name as the property in the VM has.
    var nameOfPropertyInVm = "ViewModelString"
    var binding = new Binding(nameOfPropertyInVm) { Mode = BindingMode.TwoWay };
    this.SetBinding(SearchStringProperty, binding);
}

虚拟机

// in the class of the ViewModel: MyViewModel
public string ViewModelStringProperty { get; set; }

请注意，这种实现完全缺乏 INotifyPropertyChanged 接口的实现.您需要正确更新此代码.

Note, that this kind of implementation lacks completely of implementation of the INotifyPropertyChanged interface. You'd need to update this code properly.

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