题
import Graphics.Win32
import System.Win32.DLL
import Control.Exception (bracket)
import Foreign
import System.Exit
main :: IO ()
main = do
mainInstance <- getModuleHandle Nothing
hwnd <- createWindow_ 200 200 wndProc mainInstance
createButton_ hwnd mainInstance
messagePump hwnd
wndProc :: HWND -> WindowMessage -> WPARAM -> LPARAM -> IO LRESULT
wndProc hwnd wmsg wParam lParam
| wmsg == wM_DESTROY = do
sendMessage hwnd wM_QUIT 1 0
return 0
| wmsg == wM_COMMAND && wParam == 1 = do
messageBox nullPtr "Yahoo!!" "Message box" 0 -- Error! Why? :(
return 0
| otherwise = defWindowProc (Just hwnd) wmsg wParam lParam
createWindow_ :: Int -> Int -> WindowClosure -> HINSTANCE -> IO HWND
createWindow_ width height wndProc mainInstance = do
let winClass = mkClassName "ButtonExampleWindow"
icon <- loadIcon Nothing iDI_APPLICATION
cursor <- loadCursor Nothing iDC_ARROW
bgBrush <- createSolidBrush (rgb 240 240 240)
registerClass (cS_VREDRAW + cS_HREDRAW, mainInstance, Just icon, Just cursor, Just bgBrush, Nothing, winClass)
w <- createWindow winClass "Button example" wS_OVERLAPPEDWINDOW Nothing Nothing (Just width) (Just height) Nothing Nothing mainInstance wndProc
showWindow w sW_SHOWNORMAL
updateWindow w
return w
createButton_ :: HWND -> HINSTANCE -> IO ()
createButton_ hwnd mainInstance = do
hBtn <- createButton "Press me" wS_EX_CLIENTEDGE (bS_PUSHBUTTON + wS_VISIBLE + wS_CHILD) (Just 50) (Just 80) (Just 80) (Just 20) (Just hwnd) (Just (castUINTToPtr 1)) mainInstance
return ()
messagePump :: HWND -> IO ()
messagePump hwnd = allocaMessage $ \ msg ->
let pump = do
getMessage msg (Just hwnd) `catch` \ _ -> exitWith ExitSuccess
translateMessage msg
dispatchMessage msg
pump
in pump
这是带有按钮的简单Win32 GUI应用程序,但是当我单击按钮时,必须有一个消息框(22行),但是有错误:
buttons.exe:时间表:不安全重新输入。也许“外国进口不安全”应该是“安全”?
我该如何解决?
解决方案
就像丹尼尔·瓦格纳(Daniel Wagner)评论的那样,这是Win32软件包中的一个错误。 MessageBoxW
必须安全地进口,因为它具有许多副作用。
这 messageBox
功能是“不安全”导入的包装器 MessageBoxW
功能。当不安全导入的不安全导入的函数导入时,Haskell假设该线程在返回之前不会调用任何Haskell代码。但是,如果您打电话 MessageBoxW
, ,Windows将向您在第30行中创建的窗口中扔出很多窗口消息,因此在您处于不安全的外国功能时,Haskell代码将运行。这也是为什么要打电话的原因 messageBox
将工作 直到 该窗口已创建。
可能的解决方法是简单地纠正函数。首先,更改
import Graphics.Win32
至
import Graphics.Win32 hiding (messageBox, c_MessageBox)
然后,复制 messageBox
和 c_MessageBox
从模块 Graphics.Win32.Misc
, , 和 unsafe
删除和/或 safe
添加:
messageBox :: HWND -> String -> String -> MBStyle -> IO MBStatus
messageBox wnd text caption style =
withTString text $ \ c_text ->
withTString caption $ \ c_caption ->
failIfZero "MessageBox" $ c_MessageBox wnd c_text c_caption style
foreign import stdcall safe "windows.h MessageBoxW"
c_MessageBox :: HWND -> LPCTSTR -> LPCTSTR -> MBStyle -> IO MBStatus
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