C#调用系统API
在Windows平台，可以利用很多系统API，而在.net平台下用C#调用系统API是比较方便而且也是比较轻松的事情。
我们可以利用C#调用API实现底层驱动程序驱动某一个部件（如串口通讯）和或者外设进行工作，也可以利用系统API实现图形化GUI功能
系统API一般分为:核心级(kernel32.dll),用户级(User32.dll), 应用级（gdi32.dll)和其他一些外设驱动等.
下面我们来看一个简单例子，用系统API获取窗口句柄。
代码
public
class
User32API
{
private
static
Hashtable processWnd
=
null
;
public
delegate
bool
WNDENUMPROC(IntPtr hwnd,
uint
lParam);
static
User32API()
{
if
(processWnd
==
null
)
{
processWnd
=
new
Hashtable();
}
}
[DllImport(
"
user32.dll
"
, EntryPoint
=
"
EnumWindows
"
, SetLastError
=
true
)]
public
static
extern
bool
EnumWindows(WNDENUMPROC lpEnumFunc,
uint
lParam);
[DllImport(
"
user32.dll
"
, EntryPoint
=
"
GetParent
"
, SetLastError
=
true
)]
public
static
extern
IntPtr GetParent(IntPtr hWnd);
[DllImport(
"
user32.dll
"
, EntryPoint
=
"
GetWindowThreadProcessId
"
)]
public
static
extern
uint
GetWindowThreadProcessId(IntPtr hWnd,
ref
uint
lpdwProcessId);
[DllImport(
"
user32.dll
"
, EntryPoint
=
"
IsWindow
"
)]
public
static
extern
bool
IsWindow(IntPtr hWnd);
[DllImport(
"
kernel32.dll
"
, EntryPoint
=
"
SetLastError
"
)]
public
static
extern
void
SetLastError(
uint
dwErrCode);
[DllImport(
"
User32.dll
"
, EntryPoint
=
"
SendMessage
"
)]
private
static
extern
int
SendMessage(IntPtr hWnd,
int
Msg,
int
wParam,
int
lParam);
Process[] processes;
const
int
WM_CLOSE
=
0x0010
;
public
void
GetCurrentWindowHandle()
{
Microsoft.Win32.RegistryKey oRegistryKey
=
Microsoft.Win32.Registry.CurrentUser.OpenSubKey(
"
Software
"
).OpenSubKey(
"
Amada Software
"
);
string
[] subKeys
=
oRegistryKey.GetSubKeyNames();
IntPtr ptrWnd
=
IntPtr.Zero;
foreach
(
string
subkey
in
subKeys)
{
processes
=
Process.GetProcessesByName(subkey);
foreach
(Process proc
in
processes)
{
uint
uiPid
=
(
uint
)proc.Id;
object
objWnd
=
processWnd[uiPid];
if
(objWnd
!=
null
)
{
ptrWnd
=
(IntPtr)objWnd;
if
(ptrWnd
!=
IntPtr.Zero
&&
IsWindow(ptrWnd))
{
SendMessage(ptrWnd, WM_CLOSE,
0
,
0
);
}
else
{
ptrWnd
=
IntPtr.Zero;
}
}
bool
bResult
=
EnumWindows(
new
WNDENUMPROC(EnumWindowsProc), uiPid);
if
(
!
bResult
&&
Marshal.GetLastWin32Error()
==
0
)
{
objWnd
=
processWnd[uiPid];
if
(objWnd
!=
null
)
{
ptrWnd
=
(IntPtr)objWnd;
SendMessage(ptrWnd, WM_CLOSE,
0
,
0
);
}
}
}
}
}
private
static
bool
EnumWindowsProc(IntPtr hwnd,
uint
lParam)
{
uint
uiPid
=
0
;
if
(GetParent(hwnd)
==
IntPtr.Zero)
{
GetWindowThreadProcessId(hwnd,
ref
uiPid);
if
(uiPid
==
lParam)
{
processWnd[uiPid]
=
hwnd;
SetLastError(
0
);
return
false
;
}
}
return
true
;
}
}