如何拦截NotifyPropertyChange事件

Question

我最近刚刚发现了一个 INotifyPropertyChange 接口。我设法在我的类中实现这个接口，一切正常。但是我想知道是否可以在代码中拦截此事件并触发函数 假设我有一个函数

DoStuff()

，并且我不想在每次 property1、property2 或 property3 更改时触发该函数。 当然，我可以将此函数放在我的类中的 set 块中，但这不是一个好主意（我认为）。

Answer 1

您是否需要它来替换现有的 NotifyPropertyChanged 事件处理程序，或者只是在调用 NotifyPropertyChanged 时调用它？

如果您指的是第二个，您可以简单地注册一个事件处理程序

edit

您可以添加一个在 NotifyPropertyChanged 上调用的事件处理程序，检查属性参数是否等于 Property1、Property2 或 Property3，并且仅然后将其转发到您要调用的实际函数。

Answer 2

窃取 Elisha 的答案来回答 Merlyn 的答案中的问题

public class AnswerViewModel : IAnswerViewModel
{
    public event PropertyChangedEventHandler PropertyChanged;

    private string property1;
    private string property2;
    private string propertyX;

    public AnswerViewModel()
    {
        PropertyChanged += (sender, args) => 
        {
            if(args.PropertyName == "Property1" || args.PropertyName == "Property2")
                DoStuff();
        }
    }

    public string Property1
    {
        get { return content; }
        set
        {
            property1 = value;
            PropertyChanged(this, new PropertyChangedEventArgs("Property1"));
        }
    }
    public string Property2
    {
        get { return content; }
        set
        {
            property2 = value;
            PropertyChanged(this, new PropertyChangedEventArgs("Property2"));
        }
    }
    public string PropertyX
    {
        get { return content; }
        set
        {
            propertyX = value;
            PropertyChanged(this, new PropertyChangedEventArgs("PropertyX"));
        }
    }

    public void DoStuff()
    {
        // this method will be called whenever PropertyChanged event raised from Property1 or Property2
    }
}

如果 DoStuff 所在的类是您可以执行的成员，

    private otherClass
    public AnswerViewModel()
    {
        PropertyChanged += (sender, args) => 
        {
            if(args.PropertyName == "Property1" || args.PropertyName == "Property2")
                otherClass.DoStuff();
        }
    }

否则您可以让 otherClass 在您的主代码中自行注册一个事件。

Answer 3

您可以从 RaisePropertyChanged() 方法触发该方法：

public int Property1
{
    get { return this.property1; }
    set
    {
        if (this.property1 != value)
        {
            this.property1 = value;
            RaisePropertyChanged("Property1");
        }
    }
}

private void RaisePropertyChanged(string propertyName)
{
     if (PropertyChanged != null)
     {
         PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
     }

     DoStuff(); // Call DoStuff here.
}

Answer 4

拦截 PropertyChanged 事件：

http://msdn.microsoft .com/en-us/library/system.componentmodel.inotifypropertychanged.propertychanged.aspx

Answer 5

如果您的意思是使用内部方法来处理此事件，您可以通过在类构造函数中注册该事件来完成。例如：

public class AnswerViewModel : IAnswerViewModel
{
    public event PropertyChangedEventHandler PropertyChanged;

    private string content;

    public AnswerViewModel()
    {
        PropertyChanged += (sender, args) => DoStuff();
    }

    public string Content
    {
        get { return content; }
        set
        {
            content = value;
            PropertyChanged(this, new PropertyChangedEventArgs("Content"));
        }
    }

    public void DoStuff()
    {
        // this method will be called whenever PropertyChanged event raised
    }
}

如果拦截方法属于其他类：

public class PropertiesInterceptor
{
    private readonly AnswerViewModel viewModel;

    private readonly List<string> propertiesToIntercept =
        new List<string> { "property1", "property2", "property3" };

    public PropertiesInterceptor(AnswerViewModel viewModel)
    {
        this.viewModel = viewModel;
        viewModel.PropertyChanged += OnPropertyChanged;
    }

    private void OnPropertyChanged(object sender, PropertyChangedEventArgs args)
    {
        if (propertiesToIntercept.Contains(args.PropertyName))
        {
            DoStuff();
        }
    }

    private void DoStuff()
    {
        // Do something with viewModel
    }
}