How to use SendMessage in C#?

In C#, the driver used by the program is event-driven instead of the original message-driven. Although the events provided by the .net framework are already very rich, the rich messages defined in the previous system have a great impact on the systemProgramming provides a convenient implementation method, so using messages in C# sometimes greatly improves the efficiency of programming.

　1 Define the message

In c#, the message needs to be defined as the original hexadecimal number in the windows system, such as

const int WM_Lbutton = 0x201; //defined Click the message with the left button of the mouse

public const int USER = 0x0400 // It is a user message defined by the windows system

2 Message sending

Message sending It is implemented through the API function SendMessage provided by windows. Its prototype is defined as

　[DllImport("User32.dll",EntryPoint="SendMessage")]
　　　private static extern int SendMessage(
　　　　　　　　　 int hWnd,　　　// handle to destination window
　　　　　　　　　 int Msg,　　　 // message
　　　　　　　　　 int wParam,　// first message parameter
　　　　　　　　　 int lParam // second message parameter
　　　 );

3 Message acceptance

In C#, any window There is also a message receiving and processing function, which is the defproc function

You can overload this function in the form to process the message

protected override void DefWndProc ( ref System.WinForms.Message m )
{
switch(m.msg)
{
case WM_Lbutton :
　///string与MFC中的CString的Format函数的使用方法有所不同
　string message = string.Format("收到消息!参数为:{0},{1}",m.wParam,m.lParam);
　MessageBox.Show(message);///显示一个消息框
　break;
default:
　base.DefWndProc(ref m);///调用基类函数处理非自定义消息。
　break;
}
}

In fact, events in C# are also processed through This is achieved by encapsulating system messages. If you do not process the

in the DefWndProc function, then it will be handed over to the system to process the message, and the system will implement the mouse click processing function through the proxy, so you You can intercept messages through the

defproc function. For example, if you want to intercept the click message of a certain button

4 Other message processing methods in C

# In C#, sometimes it is necessary to preprocess the messages of control. For example, if you use owc's spreadsheet control to process Excel files, you don't want users to be able to select

data for editing. , you can block mouse events. At this time, you must intercept the events predefined by the system (this is called subclassing in MFC). You can implement the message through an interface

IMessageFilter provided by C#. filter

public class Form1: System.Windows.Forms.Form,IMessageFilter
{
　const int WM_MOUSEMOVE = 0x200
　public bool PreFilterMessage(ref Message m)　
　{　 Keys keyCode = (Keys)(int)m.WParam & Keys.KeyCode;　
　　　if(m.Msg == m.Msg==WM_MOUSEMOVE) //||m.Msg == WM_LBUTTONDOWN
　　　{
　　　　//MessageBox.Show("Ignoring Escape...");　　
　　　　return true;　
　　　}　
　　　 return false;　
　}
}

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