winapi - 如果我将wndproc函数分配给wndclass，则会发生错误

Question

我用rust和winapi编码了简单的窗口应用程序。当我将DefWindowProcW函数分配给lpfnWndProc结构的WndClass字段时，代码可以正常工作。但是，当我分配我定义的WndProc函数时，该窗口不会出现，甚至不会出现用于异常处理的消息框。我想知道为什么它不起作用以及如何解决。
这是我定义的WndClass结构。

    let WndClass = WNDCLASSW {
        style: CS_HREDRAW | CS_VREDRAW,
        lpfnWndProc: Some( DefWindowProcW ),
        cbClsExtra: 0,
        cbWndExtra: 0,
        hInstance,
        hIcon: LoadIconW( null_mut(), IDC_ARROW ),
        hCursor: LoadCursorW( null_mut() , IDI_APPLICATION ),
        hbrBackground: GetStockObject(WHITE_BRUSH as i32) as HBRUSH,
        lpszMenuName: null_mut(),
        lpszClassName:lpszClass.as_ptr(),
    };

这是完整的代码。

extern crate winapi;

use self::winapi::{
    shared::{
        windef::{HWND, HBRUSH},
        minwindef::{LPARAM, WPARAM, UINT, LRESULT},
    },
    um::{
        wingdi::{GetStockObject, WHITE_BRUSH},
        libloaderapi::GetModuleHandleW,
        winuser::{
            RegisterClassW, 
            CreateWindowExW, 
            GetMessageW, 
            TranslateMessage, 
            DispatchMessageW, 
            PostQuitMessage,
            DefWindowProcW, 
            LoadIconW, 
            LoadCursorW,
            MessageBoxW,
            ShowWindow,
            MSG, 
            WS_OVERLAPPEDWINDOW, 
            WS_VISIBLE,
            CW_USEDEFAULT, 
            WNDCLASSW, 
            SW_SHOWDEFAULT,
            CS_HREDRAW, 
            CS_VREDRAW,
            MB_OK, 
            IDC_ARROW, 
            IDI_APPLICATION
        },
    }
};

use std::ptr::{ null, null_mut };
use std::ffi::OsStr;
use std::os::windows::ffi::OsStrExt;
use std::iter::once;

#[cfg(windows)]
fn win32_string( value : &str ) -> Vec<u16> {
    OsStr::new( value ).encode_wide().chain( once( 0 ) ).collect()
}

unsafe fn handle_message( handle: HWND, message: &mut MSG ) -> bool {
    if GetMessageW(message, handle, 0, 0) > 0 {
        TranslateMessage(message);
        DispatchMessageW(message);
        true
    } else {
        false
    }
}

fn main() {
    unsafe{
        let mut hWnd: HWND;
        let mut Message: MSG = std::mem::zeroed();
        let mut hInstance = GetModuleHandleW( std::ptr::null_mut() );
        let lpszClass =  win32_string("First Window");
        let mut g_hInst = hInstance;

        let WndClass = WNDCLASSW {
            style: CS_HREDRAW | CS_VREDRAW,
            lpfnWndProc: Some( DefWindowProcW ),
            cbClsExtra: 0,
            cbWndExtra: 0,
            hInstance,
            hIcon: LoadIconW( null_mut(), IDC_ARROW ),
            hCursor: LoadCursorW( null_mut() , IDI_APPLICATION ),
            hbrBackground: GetStockObject(WHITE_BRUSH as i32) as HBRUSH,
            lpszMenuName: null_mut(),
            lpszClassName:lpszClass.as_ptr(),
        };

        RegisterClassW( &WndClass );

        hWnd = CreateWindowExW(
            0,
            lpszClass.as_ptr(),
            lpszClass.as_ptr(),
            WS_OVERLAPPEDWINDOW,
            CW_USEDEFAULT,
            CW_USEDEFAULT,
            CW_USEDEFAULT,
            CW_USEDEFAULT,
            null_mut(),
            null_mut(),
            hInstance,
            null_mut()
        );

        if hWnd.is_null() {
            let title = win32_string("Error!");
            let text = win32_string("Creating window is faield");
        
            let ret = MessageBoxW(0 as HWND, text.as_ptr(), title.as_ptr(), MB_OK);
        } else {
            loop {
                if !handle_message(0 as HWND, &mut Message) {
                    break;
                }
            }
        }
    }
}

#[cfg(windows)]
unsafe extern "system" fn WndProc(hWnd: HWND, iMessage: UINT, wParam: WPARAM, lParam: LPARAM) -> LRESULT {
    match iMessage {
        WM_DESTROY => {
            PostQuitMessage(0);
            0
        },
        _ => DefWindowProcW(hWnd, iMessage, wParam, lParam)
    }
}

Answer 1

如果使用类似if的条件，则不会引用此win32常量WM_DESTROY:

if iMessage == WM_DESTROY {
        PostQuitMessage(0);
    }

然后，您将得到编译错误:

error[E0425]: cannot find value `WM_DESTROY` in this scope

只需添加 WM_DESTROY:

use self::winapi::{
    shared::{
        windef::{HWND, HBRUSH},
        minwindef::{LPARAM, WPARAM, UINT, LRESULT,ATOM},
    },
    um::{
        errhandlingapi::GetLastError,
        wingdi::{GetStockObject, WHITE_BRUSH},
        libloaderapi::GetModuleHandleW,
        winuser::{
            RegisterClassW, 
            ...,
            IDI_APPLICATION,
            WM_DESTROY
        },
    }
};

另外，创建窗口后，需要显示带有 ShowWindow的窗口:

...
lpfnWndProc: Some( WndProc ),
...
if hWnd.is_null() {
    let title = win32_string("Error!");
    let text = win32_string("Creating window is faield");

    let ret = MessageBoxW(0 as HWND, text.as_ptr(), title.as_ptr(), MB_OK);
} else {
    println!("successful");
    ShowWindow(hWnd, SW_SHOWDEFAULT);
    loop {
        if !handle_message(0 as HWND, &mut Message) {
            break;
        }
    }
}

然后它对我有用。