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C# - trigger key down event for active control

I found command System.Windows.Forms.SendKeys.Send() for sending keypress some key. This function work if open external app like a notepad and set focus and I will be see that my Key printed in this text field. How do same but with key down event, System.Windows.Forms.SendKeys.SendDown("A");, for example?
I tried call in Timer this command System.Windows.Forms.SendKeys.Send() but have runtime error associated with very fast taped.

You can't use the SendKeys class for that, unfortunately. You will need to go to a lower level API.
Poking a window with a keydown message
In Windows, keyboard events are sent to windows and controls via the Windows message pump. A piece of code using PostMessage should do the trick:
[DllImport("user32.dll")]
static extern bool PostMessage(IntPtr hWnd, uint Msg, int wParam, int lParam);
const uint WM_KEYDOWN = 0x0100;
void SendKeyDownToProcess(string processName, System.Windows.Forms.Keys key)
{
Process p = Process.GetProcessesByName(processName).FirstOrDefault();
if (p != null)
{
PostMessage(p.MainWindowHandle, WM_KEYDOWN, (int)key, 0);
}
}
Note that the application receiving these events may not do anything with it until a corresponding WM_KEYUP is received. You can get other message constants from here.
Poking a control other than the main window
The above code will send a keydown to the "MainWindowHandle." If you need to send it to something else (e.g. the active control) you will need to call PostMessage with a handle other than p.MainWindowHandle. The question is... how do you get that handle?
This is actually very involved... you will need to temporarily attach your thread to the window's message input and poke it to figure out what the handle is. This can only work if the current thread exists in a Windows Forms application and has an active message loop.
An explanation can be found here, as well as this example:
using System.Runtime.InteropServices;
public partial class FormMain : Form
{
[DllImport("user32.dll")]
static extern IntPtr GetForegroundWindow();
[DllImport("user32.dll")]
static extern IntPtr GetWindowThreadProcessId(IntPtr hWnd, IntPtr ProcessId);
[DllImport("user32.dll")]
static extern IntPtr AttachThreadInput(IntPtr idAttach,
IntPtr idAttachTo, bool fAttach);
[DllImport("user32.dll")]
static extern IntPtr GetFocus();
public FormMain()
{
InitializeComponent();
}
private void timerUpdate_Tick(object sender, EventArgs e)
{
labelHandle.Text = "hWnd: " +
FocusedControlInActiveWindow().ToString();
}
private IntPtr FocusedControlInActiveWindow()
{
IntPtr activeWindowHandle = GetForegroundWindow();
IntPtr activeWindowThread =
GetWindowThreadProcessId(activeWindowHandle, IntPtr.Zero);
IntPtr thisWindowThread = GetWindowThreadProcessId(this.Handle, IntPtr.Zero);
AttachThreadInput(activeWindowThread, thisWindowThread, true);
IntPtr focusedControlHandle = GetFocus();
AttachThreadInput(activeWindowThread, thisWindowThread, false);
return focusedControlHandle;
}
}
The good news-- if SendKeys worked for you, then you might not need to do all this-- SendKeys also sends messages to the main window handle.

Closing Personalization window using c#

I have written a program that change the windows theme but after changing the theme personalization window remains open and I want to close it. I tried using process.kill() with familiar process name but it didn't work. Thank you.
The code for what I am doing is as below:
ProcessStartInfo theinfo = new ProcessStartInfo(themepath + "aero.theme");
theinfo.CreateNoWindow = true;
Process thepr = new Process();
thepr.StartInfo = theinfo;
thepr.Start();
where "themepath" is String location to aero.theme.
I have even enabled CreateNoWindow to true then also it opens up Personalization to change theme but didn't close it automatically.

First use find window to get the window from their name by Using FindWindow..
[DllImport("user32.dll")]
public static extern int FindWindow(string lpClassName,string lpWindowName);
It returns you the handle of the window you want now you can use send message to close it..
[DllImport("User32.dll")]
public static extern int SendMessage(int hWnd, uint Msg, int wParam, int lParam);
public const int WM_SYSCOMMAND = 0x0112;
public const int SC_CLOSE = 0xF060;
private void closeWindow()
{
// retrieve the handler of the window
int iHandle = FindWindow("CabinetWClass", "Personalization");
if (iHandle > 0)
{
SendMessage(iHandle, WM_SYSCOMMAND, SC_CLOSE, 0);
}
}

You need to obtain the window handle by it's name and then send it a close message. This prevents having to kill any processes. See this article for information on obtaining the windows. See this one for closing windows from the handle.
After seeing the code and doing a little digging, you can accomplish this with two registry edits. You should read this article and just have your program edit the two registry keys in question.

Capture Key press globally but suppress only for current app and child windows regardless of focus

I'm running into a weird problem.
I have a WinForms application that opens another program (billing system emulator), sets it as a child window and then disables it. This works fine, the user cannot send any keys to the that child window, and the winforms application does its thing, sending commands to the child window.
However, it's been discovered that pushing the shift or control, even if the winforms application doesn't have focus, causes an error in the billing system emulator as they aren't valid keys. Users have taken to not using the shift or control keys while the winforms app runs but that's obviously not a practical solution.
My attempted solution was:
Global keyboard hook to capture when those keys are pressed.
Overriding OnKeyDown in the winforms application to stop those keys.
That however still doesn't solve the problem of the shift and alt keys being sent to the child window when the winforms app is not in focus. I can stop shift and alt globally while the winforms app is running but I don't think that is valid. So I need to somehow in the global hook stop the keypress for the winforms app and its children but allow globally. Any ideas/thoughts?
This is my code.

I don't think there's a good answer for your scenario... =\
Here's a hack you can try. It will "release" Control/Shift if they are down, then you send your message afterwards:
[DllImport("user32.dll", CharSet = CharSet.Auto, ExactSpelling = true, CallingConvention = CallingConvention.Winapi)]
public static extern void keybd_event(byte bVk, byte bScan, int dwFlags, int extraInfo);
[DllImport("user32.dll")]
static extern short MapVirtualKey(int wCode, int wMapType);
private void button1_Click(object sender, EventArgs e)
{
if ((Control.ModifierKeys & Keys.Shift) == Keys.Shift)
{
keybd_event((int)Keys.ShiftKey, (byte)MapVirtualKey((int)Keys.ShiftKey, 0), 2, 0); // Shift Up
}
if ((Control.ModifierKeys & Keys.Control) == Keys.Control)
{
keybd_event((int)Keys.ControlKey, (byte)MapVirtualKey((int)Keys.ControlKey, 0), 2, 0); // Control Up
}
// ... now try sending your message ...
}
This obviously isn't foolproof.

I took a look at the only constructor of the globalKeyboardHook and looks like it is designed only for global hook. You can add another overload to hook into the current running module only like this:
class globalKeyboardHook {
[DllImport("kernel32")]
private static extern int GetCurrentThreadId();
[DllImport("user32")]
private static extern IntPtr SetWindowsHookEx(int hookType, KeyBoardProc proc, IntPtr moduleHandle, int threadId);
[DllImport("user32")]
private static extern int CallNextHookEx(IntPtr hHook, int nCode, IntPtr wParam, IntPtr lParam);
public globalKeyboardHook(bool currentModuleOnly){
if(currentModuleOnly){
proc = KeyBoardCallback;
//WH_KEYBOARD = 0x2
hhook = SetWindowsHookEx(2, proc, IntPtr.Zero, GetCurrentThreadId());
} else hook();
}
public delegate int KeyBoardProc(int nCode, IntPtr wParam, IntPtr lParam);
public int KeyBoardCallback(int nCode, IntPtr wParam, IntPtr lParam) {
if (nCode >= 0) {
Keys key = (Keys)wParam;
var lp = lParam.ToInt64();
//your own handling with the key
if ((lp >> 31) == 0)//Key down
{
//your own code ...
} else { //Key up
//your own code ...
}
}
return CallNextHookEx(hHook, nCode, wParam, lParam);
}
KeyBoardProc proc;
//other code ...
}
//then use the new overload constructor instead of the parameterless constructor:
globalHook = new globalKeyboardHook(true);
NOTE: You can implement your own KeyDown and KeyUp event based on what I posted above (the comment your own code ...). After some searching I understand that the WH_KEYBOARD_LL supports global hook only while the WH_KEYBOARD is for thread hook only. That should be what you want instead of the WH_KEYBOARD_LL.
BTW, I doubt that the IMessageFilter which can be registered/added by your application can be used in this case. It also supports a PreFilterMessage method helping you to intercept any key and mouse messages at the application-level. You should try searching on that, it's easy to follow.

Is there a way to have my app push its icon to other apps?

I have a WPF app that starts another application, I'd like for my application to change the Icon of this second app. I am able to use GetWindowText and SetWindowText to change the title. Is it possible to do this for the Icon as well?
update
I have no control of the second app.

To change the window title of another application:
Definitions of Win32 API functions and constants:
[DllImport("user32.dll", SetLastError = true, CharSet = CharSet.Auto)]
public static extern bool SetWindowText(IntPtr hwnd, String lpString);
[DllImport("user32.dll")]
public static extern int SendMessage(IntPtr hwnd, int message, int wParam, IntPtr lParam);
private const int WM_SETICON = 0x80;
private const int ICON_SMALL = 0;
private const int ICON_BIG = 1;
Usage:
Process process = Process.Start("notepad");
// If you have just started a process and want to use its main window handle,
// consider using the WaitForInputIdle method to allow the process to finish starting,
// ensuring that the main window handle has been created.
// Otherwise, an exception will be thrown.
process.WaitForInputIdle();
SetWindowText(process.MainWindowHandle, "Hello!");
Icon icon = new Icon(#"C:\Icon\File\Path.ico");
SendMessage(process.MainWindowHandle, WM_SETICON, ICON_BIG, icon.Handle);

In Windows Forms you would use
Icon ico = Icon.ExtractAssociatedIcon(#"C:\WINDOWS\system32\notepad.exe");
this.Icon = ico;
So im guessing for WPF it would be similar.

Sending Keyboard Macro Commands to Game Windows

I wanna do a macro program for a game. But there is a problem with sending keys to only game application (game window). I am using keybd_event API for sending keys to game window. But I only want to send keys to the game window, not to explorer or any opened window while my macro program is running. When I changed windows its still sending keys. I tried to use Interaction.App with Visual Basic.dll reference. But Interaction.App only Focus the game window.
I couldn't find anything about my problem. Can anyone help me? Thanx

i fixed my problem.
in this field ;
PostMessage(hWnd, WM_KEYDOWN, key, {have to give lParam of the key});
otherwise it does not work.And we can control of ChildWindow Class with Spy++ tool of Microsoft.
Thanks everyone for helping.

Are you retrieving the handle of the window all the time, or are you remembering it?
If you use the FindWindow() API, you can simply store the Handle and use the SendMessage API to send key/mouse events manually.

FindWindow API:
http://www.pinvoke.net/default.aspx/user32.FindWindowEx
SendMessage API:
http://www.pinvoke.net/default.aspx/user32/SendMessage.html
VB
Private Const WM_KEYDOWN As Integer = &H100
Private Const WM_KEYUP As Integer = &H101
C#
private static int WM_KEYDOWN = 0x100
private static int WM_KEYUP = 0x101

class SendKeySample
{
private static Int32 WM_KEYDOWN = 0x100;
private static Int32 WM_KEYUP = 0x101;
[return: MarshalAs(UnmanagedType.Bool)]
[DllImport("user32.dll", SetLastError = true)]
static extern bool PostMessage(IntPtr hWnd, int Msg, System.Windows.Forms.Keys wParam, int lParam);
[DllImport("user32.dll", SetLastError = true)]
private static extern IntPtr FindWindowEx(IntPtr hwndParent, IntPtr hwndChildAfter, string lpszClass, string lpszWindow);
public static IntPtr FindWindow(string windowName)
{
foreach (System.Diagnostics.Process p in System.Diagnostics.Process.GetProcesses())
{
if (p.MainWindowHandle != IntPtr.Zero && p.MainWindowTitle.ToLower() == windowName.ToLower())
return p.MainWindowHandle;
}
return IntPtr.Zero;
}
public static IntPtr FindWindow(IntPtr parent, string childClassName)
{
return FindWindowEx(parent, IntPtr.Zero, childClassName, string.Empty);
}
public static void SendKey(IntPtr hWnd, System.Windows.Forms.Keys key)
{
PostMessage(hWnd, WM_KEYDOWN, key, 0);
}
}
Calling Code
var hWnd = SendKeySample.FindWindow("Untitled - Notepad");
var editBox = SendKeySample.FindWindow(hWnd, "edit");
SendKeySample.SendKey(editBox, Keys.A);

If you want to communicate with a game, you typically will have to deal with DirectInput, not the normal keyboard API's.