WinForms中的按钮具有CLICK事件。 但是谁告诉按钮对象已被单击呢？

Question

I am learning C#. I was going through the Events and Delegates part of the language. I am working on a WinForms application for educating myself. I tried looking deep for understanding Buttons and how they work. I found the following:

1) There is a line public partial class Form1 : Form in my default Form1.cs file. This is a partial class.

2) I also have a Form1.Designer.cs class file that has a line partial class Form1 . Now the files mentioned in 1) and 2) combine to form a full class.

3) The From1.Designer.cs file has a lot of statements that eventually create the button object. It also has a statement that is of particular interest to me:

 this.btn_BaseBuildLocation.Click += new System.EventHandler(this.btn_BaseBuildLocation_Click); 

This statement adds a custom function to the delegate Click. This delegate is declared in the Control class (System.Windows.Forms.dll) as follows:

 public event EventHandler Click; 

4) The EventHandler is a delegate defined in System.EventHandler.cs (mscorlib.dll).

5) The Button class inherits Control class and thus has access to the Click EventHandler.

6) The Button class has all the logic to handle the flow once it knows that someone has clicked it. I had a look at the Button class used in Mono for understanding the inner details. I do this for almost all classes that I want to learn.

7) All this is extremely beautiful. But I was troubled by the fact that I did not know how the Button object knows that it has been clicked.

8) I went through VC++ and how it handles the events. I found a lot about Message Loops, Event Queues etc...

Questions:

1) Is the VC++ way of handling events the same as .NET's?

2) If so, is there a way to look into those details?

Any help would be appreciated. Thanks.

Answer 1

A Button is, technically, a Window. It has a Window handle.

That means that the Dispatcher will route keyboard and mouse events to the Button when appropriate. The Button has internal logic to determine when a MouseDown and a MouseUp event constitute a valid click and then it raises the Click event.

Answer 2

1. 1) Is the VC++ way of handling events the same as .NET's?

   Yes obviously, handling is same, it is done by capturing the window messages and respond accordingly. .Net provides a wrapper around window handles 'NativeWindow class' which is low level encapsulation of a Window Handle , System.Windows.Forms.Control is the base class for all Controls which internally uses decendant of NativeWindow named ControlNativeWindow which passes all Messages to Control.

2. If so, is there a way to look into those details?

   Yes, dig into Control class Through Reflector

hope this helps

Answer 3

In WinForm appplicatio you have Program class with Main method. There is always one line there:

Application.Run(new YourMainForm());

It begins running a standard application message loop on the current thread. That's the "starting point" for events.

Answer to this question explains it prertty well and also links to some sources

Answer 4

A WinForms Button is a managed wrapper around the unmanaged Windows type which is created and managed via a set of Win32 API calls that .NET performs P/Invoke on.

Deep down, the button subscribes to the same Window Event Loop (or Message Pump if you prefer) which drives the Win32 API calls you may have seen in VC++ examples. The unmanaged Windows runtime puts events (like "this button has been clicked") onto the event queue. When the loop executes, the queued event is picked up by the relevant control and is propagated into a "managed" event which is when you are able to observe it.

In essence, the Windows runtime is providing much of the infrastructure and .NET only provides a convenient set of wrappers which make it easy to work with the clunky old Win32 libraries.

You can discover a lot of this for yourself if you use Reflector and dig into Button and Control to just see where the .NET code ends and the unmanaged Win32 calls begin.