当变量更改时收到通知

Question

有什么方法可以获取变量何时更改吗？如果是这样，我怎样才能实现这一目标？

Answer 1

“官方”的做法是INotifyPropertyChanged。例如，当控件绑定的数据对象更新时，UI（Windows 窗体、WPF）使用它来自动刷新控件。

public class MyClass : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;

    private void OnPropertyChanged(string propertyName)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }

    ...
}

然后你可以实现这样的属性

private string _name;
public string Name
{
    get { return _name; }
    set {
        if (value != _name) {
            _name = value;
            OnPropertyChanged(nameof(Name));
        }
    }
}

你可以这样使用它：

var myObj = new MyClass();
myObj.PropertyChanged += MyObj_PropertyChanged;

myObj.Name = "new name";

// Clean up (e.g. in a `Dispose()` method)
myObj.PropertyChanged -= MyObj_PropertyChanged;

假设这个事件处理程序：

// Will be called whenever a property of `MyClass` is updated.
private void MyObj_PropertyChanged(object sender, PropertyChangedEventArgs e)
{
    // Example
    if (e.PropertyName == nameof(MyClass.Name)) {
        var myObj = (MyClass)sender;
        //TODO: do something.
    }
}