Shulou(Shulou.com)06/03 Report--

This article will explain in detail how to pass the parameters of SendMessage and PostMessage in C#. The content of the article is of high quality, so the editor shares it for you as a reference. I hope you will have some understanding of the relevant knowledge after reading this article.

In C #, you can use SendMessage and PostMessage provided by Window API to pass parameters. The difference between the two is briefly introduced: for the difference in return values, let's first take a look at the declaration in MSDN:

LRESULT SendMessage (

HWND hWnd

UINT Msg

WPARAM wParam

LPARAM lParam

);

BOOL PostMessage (

HWND hWnd

UINT Msg

WPARAM wParam

LPARAM lParam

);

Four of the parameters have the same meaning, and the return values are of different types (in fact, they are a 32-bit number in terms of data, but the meaning is different). LRESULT represents the return value after the message is processed, and BOOL indicates whether the message is successful or not.

2. PostMessage is asynchronous and SendMessage is synchronous.

PostMessage only puts the message into the queue and returns regardless of whether the message is processed or not, the message may not be processed, while SendMessage waits for the message to be processed before it returns, and if the message is not processed, the thread that sends the message will always be blocked.

3. If the message is sent by SendMessage in the same thread, the USER32.DLL

The module calls the message handler of the target window and returns the result. SendMessage does not join the thread message queue when sending messages in the same thread. PostMessage

When sending a message, the message is first put into the thread's message queue and then dispatched to the target window (DispatchMessage) through the message loop.

If within a different thread, SendMessage sends a message to the message queue of the thread to which the target window belongs, and then the thread that sends the message is in the USER32.DLL

Monitor and wait for message processing within the module until the target window returns after processing. SendMessage also does a lot of work before returning, for example, responding to other threads to it

SendMessage . When Post goes to another thread, it is best to use PostThreadMessage instead

The hWnd parameter of PostMessage,PostMessage can be NULL, which is equivalent to PostThreadMessage +

GetCurrentThreadId . When Post WM_QUIT, you should use PostQuitMessage instead.

4. The system only marshal system messages (messages between 0 and WM_USER). When sending user messages (above WM_USER) to other processes, you need to do your own reorganization.

When sending system messages with asynchronous functions such as PostMessage, SendNotifyMessage, SendMessageCallback, etc., pointers cannot be used in parameters, because the sender does not wait for the message to be processed before returning, and the receiver releases the pointer before it is processed. 5. In Windows 2000/XP, each message queue can only store a maximum of 10000 Post messages. Those that have not been processed will not be processed and will be discarded directly. This value can be changed to a larger value: [HKEY_LOCAL_MACHINE/SOFTWARE/ Microsoft/Windows NT/CurrentVersion/Windows] USERPostMessageLimit, with a minimum of 4000. PostMessage is only responsible for putting the message into the message queue. It is uncertain when and whether to process SendMessage. It is necessary to wait until the return code (DWord type) of the message is processed before continuing with the PostMessage execution. SendMessage will not be returned until the message has been processed. The following is a small example to illustrate the difference between the two methods in passing parameters:

/ / Win32 API class

Using System

Using System.Runtime.InteropServices

Namespace TestHwnd

{

Public class Win32API

{

[DllImport ("User32.dll", EntryPoint = "FindWindow")]

Public static extern IntPtr FindWindow (string lpClassName, string lpWindowName)

[DllImport ("User32.dll", EntryPoint = "FindWindowEx")]

Public static extern IntPtr FindWindowEx (IntPtr hwndParent, IntPtr hwndChildAfter, string lpClassName, string lpWindowName)

/ / /

/ / Custom structure

/ / /

/ / Note: the structure body must not be a class, that is, the struct keyword must not be class, otherwise an exception will be generated when receiving the message.

Public struct My_lParam

{

Public int i

Public string s

}

/ / /

/ / use COPYDATASTRUCT to pass strings

/ / /

[StructLayout (LayoutKind.Sequential)]

Public struct COPYDATASTRUCT

{

Public IntPtr dwData

Public int cbData

[MarshalAs (UnmanagedType.LPStr)]

Public string lpData

}

/ / API for sending messages

[DllImport ("User32.dll", EntryPoint = "SendMessage")]

Public static extern int SendMessage (

IntPtr hWnd, / / handle to the window to which the message is sent

Int Msg, / / message ID

Int wParam, / / Parameter 1

Int lParam / / Parameter 2

);

/ / API for sending messages

[DllImport ("User32.dll", EntryPoint = "SendMessage")]

Public static extern int SendMessage (

IntPtr hWnd, / / handle to the window to which the message is sent

Int Msg, / / message ID

Int wParam, / / Parameter 1

Ref My_lParam lParam / / Parameter 2

);

/ / API for sending messages

[DllImport ("User32.dll", EntryPoint = "SendMessage")]

Public static extern int SendMessage (

IntPtr hWnd, / / handle to the window to which the message is sent

Int Msg, / / message ID

Int wParam, / / Parameter 1

Ref COPYDATASTRUCT lParam / / Parameter 2

);

/ / API for sending messages

[DllImport ("User32.dll", EntryPoint = "PostMessage")]

Public static extern int PostMessage (

IntPtr hWnd, / / handle to the window to which the message is sent

Int Msg, / / message ID

Int wParam, / / Parameter 1

Int lParam / / Parameter 2

);

/ / API for sending messages

[DllImport ("User32.dll", EntryPoint = "PostMessage")]

Public static extern int PostMessage (

IntPtr hWnd, / / handle to the window to which the message is sent

Int Msg, / / message ID

Int wParam, / / Parameter 1

Ref My_lParam lParam / / Parameter 2

);

/ / Asynchronous message sending API

[DllImport ("User32.dll", EntryPoint = "PostMessage")]

Public static extern int PostMessage (

IntPtr hWnd, / / handle to the window to which the message is sent

Int Msg, / / message ID

Int wParam, / / Parameter 1

Ref COPYDATASTRUCT lParam / / Parameter 2

);

}

}

/ / main form, send messages

Using System

Using System.Collections.Generic

Using System.ComponentModel

Using System.Data

Using System.Drawing

Using System.Linq

Using System.Text

Using System.Windows.Forms

Using System.Runtime.InteropServices

Namespace TestHwnd

{

Public partial class Main: Form

{

Public IntPtr hwndTest

Public int IwndTest

Public IntPtr hwndfrmTest

Public Main ()

{

InitializeComponent ()

}

Private void button1_Click (object sender, EventArgs e)

{

Test test = new Test ()

Test.Show (this)

}

Private void timer1_Tick (object sender, EventArgs e)

{

String strTest = "25425"

Win32API.COPYDATASTRUCT cds

Cds.dwData = (IntPtr) 100

Cds.lpData = strTest

Byte [] sarr = System.Text.Encoding.UTF8.GetBytes (strTest)

Int len = sarr.Length

Cds.cbData = len + 1

Win32API.My_lParam lp=new Win32API.My_lParam ()

Lp.i=3

Lp.s= "test"

If (hwndTestrated = (IntPtr) 0)

{

If (DateTime.Now.Second% 2 = = 0)

{

Win32API.SendMessage (hwndTest, 0x60, 1,3); / / passed 2 integer parameters successfully

}

If (DateTime.Now.Second% 3 = = 0)

{

Win32API.SendMessage (hwndTest, 0x61, 5, ref lp); / / passed integer parameters and structure types successfully. This method can be changed to pass objects.

}

If (DateTime.Now.Second% 5 = = 0)

{

Win32API.SendMessage (hwndTest, 0x62, 5, ref cds); / / passed integer parameters and variable length string successfully

}

If (DateTime.Now.Second% 7 = = 0)

{

Win32API.PostMessage (hwndTest, 0x63, 5, 6); / / passed 2 integer parameters successfully

}

If (DateTime.Now.Second% 9 = = 0)

{

Win32API.PostMessage (hwndTest, 0x64, 3, ref lp); / / the integer parameter was passed successfully, but the parameter lp failed. 3 can be passed successfully.

}

If (DateTime.Now.Second% 11 = = 0)

{

Win32API.PostMessage (hwndTest, 0x65, 3, ref cds); / / the integer parameter was passed successfully, the parameter cds failed, and 3 can be passed successfully.

}

}

}

}

}

/ / Sub-form receives messages and parameters

Using System

Using System.Collections.Generic

Using System.ComponentModel

Using System.Data

Using System.Drawing

Using System.Linq

Using System.Text

Using System.Windows.Forms

Using System.Runtime.InteropServices

Namespace TestHwnd

{

Public partial class Test: Form

{

Main main

Public Test ()

{

InitializeComponent ()

}

Private void Test_Load (object sender, EventArgs e)

{

Main = this.Owner as Main

Main.hwndTest = this.Handle

}

/ / rewrite the message handling function DefWndProc of the form to add the processing entry for self-defined message detection

Protected override void DefWndProc (ref Message m)

{

Switch (m.Msg)

{

/ / receive the custom message MYMESSAGE and display its parameters

Case 0x60:

{

Label1.Text = DateTime.Now.ToString () + "-" + m.WParam.ToInt32 (). ToString () + "-" + m.LParam.ToInt32 () .ToString ()

}

Break

Case 0x61:

{

Win32API.My_lParam ml = new Win32API.My_lParam ()

Type t = ml.GetType ()

Ml = Win32API.My_lParam) m.GetLParam (t)

Label2.Text = DateTime.Now.ToString () + "-" + m.WParam.ToInt32 (). ToString () + "-" + ml.i.ToString () + ":" + ml.s

}

Break

Case 0x62:

{

Win32API.COPYDATASTRUCT mystr = new Win32API.COPYDATASTRUCT ()

Type mytype = mystr.GetType ()

Mystr = (Win32API.COPYDATASTRUCT) m.GetLParam (mytype)

String str2 = mystr.lpData

Label3.Text = DateTime.Now.ToString () + "-" + m.WParam.ToInt32 (). ToString () + "-" + str2

}

Break

Case 0x63:

{

Label4.Text = DateTime.Now.ToString () + "-" + m.WParam.ToInt32 (). ToString () + "-" + m.LParam.ToInt32 () .ToString ()

}

Break

Case 0x64:

{

Win32API.My_lParam ml = new Win32API.My_lParam ()

Type t = ml.GetType ()

Ml = Win32API.My_lParam) m.GetLParam (t)

Label5.Text = DateTime.Now.ToString () + "-" + m.WParam.ToInt32 (). ToString () + "-" + ml.i.ToString () + ":" + ml.s

}

Break

Case 0x65:

{

Win32API.COPYDATASTRUCT mystr = new Win32API.COPYDATASTRUCT ()

Type mytype = mystr.GetType ()

Mystr = (Win32API.COPYDATASTRUCT) m.GetLParam (mytype)

String str2 = mystr.lpData

Label6.Text = DateTime.Now.ToString () + "-" + m.WParam.ToInt32 (). ToString () + "-" + str2

}

Break

Default:

Base.DefWndProc (ref m)

Break

}

}

Private void button1_Click (object sender, EventArgs e)

{

Main.hwndTest = (IntPtr) (0)

This.Close ()

}

}

}

On how to carry out the parameter transfer of SendMessage and PostMessage in C# is shared here, I hope the above content can be of some help to you, can learn more knowledge. If you think the article is good, you can share it for more people to see.

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.