如何在 ViewModel 中订阅 PropertyChanged 事件？

发布于 2024-12-10 23:49:13 字数 381 浏览 0 评论 0原文

我将核心功能封装在 ViewModelBase 中

现在我想查看 ViewModelBase 何时引发 PropertyChanged 事件并对其采取行动。例如，当 ViewModelBase 上的一个属性发生更改时 - 我想更改 ViewModel 上的属性，

如何实现这一目标？

public class MaintainGroupViewModel : BaseViewModel<MEMGroup>
    {


public abstract class BaseViewModel<T> : NotificationObject, INavigationAware
        where T : Entity
    {

原文

I have core functionality encapsulated in ViewModelBase

Now I want to see when PropertyChanged event was raised by ViewModelBase and act on it. For example, when one property was changed on ViewModelBase - I want to change property on my ViewModel

How do I achieve this?

public class MaintainGroupViewModel : BaseViewModel<MEMGroup>
    {


public abstract class BaseViewModel<T> : NotificationObject, INavigationAware
        where T : Entity
    {

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禾厶谷欠 2024-12-17 23:49:13

通常我在类构造函数中使用注册到 PropertyChanged 事件

public MyViewModel()
{
    this.PropertyChanged += MyViewModel_PropertyChanged;
}

，我的 PropertyChanged 事件处理程序如下所示：

void MyViewModel_PropertyChanged(object sender, PropertyChangedEventArgs e)
{
    switch (e.PropertyName)
    {
        case "SomeProperty":
            // Do something
            break;
    }
}

Usually I use register to the PropertyChanged event in the class Constructor

public MyViewModel()
{
    this.PropertyChanged += MyViewModel_PropertyChanged;
}

and my PropertyChanged event handler looks like this:

void MyViewModel_PropertyChanged(object sender, PropertyChangedEventArgs e)
{
    switch (e.PropertyName)
    {
        case "SomeProperty":
            // Do something
            break;
    }
}

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不羁少年 2024-12-17 23:49:13

我担心您实际上正在对派生类中的属性进行“手动绑定”（不好）到基类上的值（也不好）。使用继承的全部意义在于派生类可以访问基类中的内容。使用 protected 修饰符来指示事物只能由派生类访问。

我建议这个（可能）更正确的方法：

基类：

protected virtual void OnMyValueChanged() { }

派生类：

protected override void OnMyValueChanged() { /* respond here */ }

真的，订阅您正在编写的类的基类中的事件似乎令人难以置信的倒退 - 如果您使用继承而不是组合，那有什么意义呢？你要让自己平静下来吗？当事情发生时，你实际上是在要求一个对象告诉自己。为此，您应该使用方法调用。

就“当 ViewModelBase 上的一个属性发生更改时 - 我想更改我的 ViewModel 上的属性”而言，...它们是同一个对象！

I am concerned that you're effectively doing a 'manual binding' (bad) for a property in a derived class to a value on the base class (also bad). The whole point of using inheritance is that the derived class can access things in the base class. Use a protected modifier to indicate things should only be accessible to derived classes.

I would suggest this (potentially) more correct method:

Base class:

protected virtual void OnMyValueChanged() { }

Derived class:

protected override void OnMyValueChanged() { /* respond here */ }

Really, subscribing to an event in the base class of the very class you're writing just seems incredibly backwards - what's the point of using inheritance over composition if you're going to compose yourself around yourself? You're literally asking an object to tell itself when something happens. A method call is what you should use for that.

In terms of "when one property was changed on ViewModelBase - I want to change property on my ViewModel", ... they are the same object!

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幸福还没到 2024-12-17 23:49:13

订阅属性更改的直接方法是使用 INotifyPropertyChanged 如果您的 BaseViewModel 实现了它：

PropertyChanged += (obj, args) =>
   { System.Console.WriteLine("Property " + args.PropertyName + " changed"); }

如果没有，那么它必须是 DependencyObject，并且您的属性必须是DependencyProperties（这可能是一种更复杂的方式）。

本文介绍如何订阅 DependencyProperty 更改。

The direct way to subscribe to property changes is using INotifyPropertyChanged if your BaseViewModel implements it:

PropertyChanged += (obj, args) =>
   { System.Console.WriteLine("Property " + args.PropertyName + " changed"); }

If it doesn't, then it has to be a DependencyObject, and your properties have to be DependencyProperties (which is probably a more complicated way).

This article describes how to subscribe for DependencyProperty changes.

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