how to catch changes in a member variable? (C#)

This seems to be basics of the language, but I do not understa开发者_如何学Gond how is this accomplished in .Net. I have a member variable in a class, say a bool _isCommitted. I want something to happen whenever _isCommitted is true. Something like this:

     //Whenever _isCommitted == true()
     {
         Foo()
     }

Basically like an event, but here it is my variable. How to? Many thanks..

This is normally done through properties and a backing private field. You need to ensure you only ever access through the property.

private bool _isCommitted;

public bool IsCommitted
{
  get { return _isCommitted; }
  set
  {
     if(value)
     {
        //do something
     }

     _isCommitted = value;
  }
}

At the most basic level, you can create an event in your class:

public delegate void MyHandler(bool b);
public event MyHandler CommittedChanged;

Now people can subscribe to your event like so:

public void SomeHandlerMethod(bool b) { ... }

...

someInstance.CommittedChanged += SomeHandlerMethod;
someInstance.CommittedChanged += ASecondHandlerMethod;
someInstance.CommittedChanged += x => { /* inline handler using lambda */ };

A user can unregister his event handler this way:

someInstance.CommittedChanged -= SomeHandlerMethod;

And wherever you decide to change your variable, you will follow it up with:

if (CommittedChanged != null) CommittedChanged(_isCommitted);

This will call everyone who has registered a function with your event.

Having said this, there are plenty of improvements that you can do. First, make _isCommitted into a property, and do the event callback in its setter. This way, you won't forget to call the handlers.

public IsCommitted { 
   get { return _isCommitted; } 
   set {  
     _isCommitted = value; 
     if (CommittedChanged != null) CommittedChanged(_isCommitted);
   }
}

Read more about events here.

This is enough to get you going. However, if you delve further into the C# framework, you will find a standardized way of using this event framework inside of the System.ComponentModel namespace. Sepcifically, the interface INotifyPropertyChanged, which ties neatly into a more generic event system that also plays well with some of Microsoft's own technologies, such as WPF, allowing GUI elements to pick up on changes to your class automatically. Read more about INotifyPropertyChanged here.

You basically need PropertyChangedEvent PropertyChangedEventHandler Delegate

I think C# properties is what you need.

private bool _isCommitted;

    public bool IsCommitted
    {
        get { return _isCommitted; }
        set { if(value){/*DO SOMETHING HERE*/}
            _isCommitted = value; }
    }