Understanding Child Windows in Rust with WinAPI

Creating Child Windows in Rust with WinAPI: A Practical Guide

This script demonstrates a corrected and optimized approach to creating a parent window with child controls in Rust using the Windows API. It includes detailed comments for better understanding and modularity.

#![allow(non_snake_case)]
use windows::
    core::*,
    Win32::Foundation::*,
    Win32::Graphics::Gdi::*,
    Win32::System::LibraryLoader::GetModuleHandleA,
    Win32::UI::WindowsAndMessaging::*;

fn main() -> Result<()> {
    unsafe {
        // Load the current instance
        let instance = GetModuleHandleA(None)?;

        // Define the window class
        let window_class = s!("window");
        let wc = WNDCLASSA {
            hCursor: LoadCursorW(None, IDC_ARROW)?,
            hInstance: instance.into(),
            lpszClassName: window_class,
            style: CS_HREDRAW | CS_VREDRAW,
            lpfnWndProc: Some(wndproc),
            ..Default::default()
        };

        // Register the window class
        let atom = RegisterClassA(&wc);
        debug_assert!(atom != 0);

        // Create the main parent window
        let _hwnd = CreateWindowExA(
            WINDOW_EX_STYLE::default(),
            window_class,
            s!("Rust WinAPI Form"),
            WS_OVERLAPPEDWINDOW | WS_VISIBLE,
            CW_USEDEFAULT,
            CW_USEDEFAULT,
            500,
            400,
            None,
            None,
            instance,
            None,
        )?;

        // Add child controls with proper styles
        CreateWindowExA(
            WINDOW_EX_STYLE::default(),
            s!("static"),
            s!("Enter your name:"),
            WS_CHILD | WS_VISIBLE,
            20,
            50,
            150,
            25,
            _hwnd,
            None,
            instance,
            None,
        );

        CreateWindowExA(
            WINDOW_EX_STYLE::default(),
            s!("edit"),
            None,
            WS_CHILD | WS_VISIBLE | WS_BORDER,
            180,
            50,
            200,
            25,
            _hwnd,
            None,
            instance,
            None,
        );

        CreateWindowExA(
            WINDOW_EX_STYLE::default(),
            s!("button"),
            s!("Submit"),
            WS_CHILD | WS_VISIBLE,
            200,
            100,
            100,
            30,
            _hwnd,
            None,
            instance,
            None,
        );

        // Display and update the main window
        ShowWindow(_hwnd, SW_SHOW);
        UpdateWindow(_hwnd);

        // Run the message loop
        let mut message = MSG::default();
        while GetMessageA(&mut message, None, 0, 0).into() {
            DispatchMessageA(&message);
        }
    }
    Ok(())
}

extern "system" fn wndproc(window: HWND, message: u32, wparam: WPARAM, lparam: LPARAM) -> LRESULT {
    unsafe {
        match message {
            WM_PAINT => {
                println!("WM_PAINT triggered");
                ValidateRect(window, None);
                LRESULT(0)
            }
            WM_DESTROY => {
                PostQuitMessage(0);
                LRESULT(0)
            }
            _ => DefWindowProcA(window, message, wparam, lparam),
        }
    }
}

Testing GUI Rendering in Rust with WinAPI

This unit test script checks the proper creation and visibility of the main window and child controls in a simulated environment.

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_window_creation() {
        unsafe {
            let instance = GetModuleHandleA(None).unwrap();
            let window_class = s!("test_window");
            let wc = WNDCLASSA {
                hCursor: LoadCursorW(None, IDC_ARROW).unwrap(),
                hInstance: instance.into(),
                lpszClassName: window_class,
                ..Default::default()
            };
            let atom = RegisterClassA(&wc);
            assert!(atom != 0);

            let _hwnd = CreateWindowExA(
                WINDOW_EX_STYLE::default(),
                window_class,
                s!("Test Form"),
                WS_OVERLAPPEDWINDOW,
                CW_USEDEFAULT,
                CW_USEDEFAULT,
                400,
                300,
                None,
                None,
                instance,
                None,
            );
            assert!(!_hwnd.is_invalid());
        }
    }
}

Frequently Asked Questions About WinAPI and Rust GUI

1. Why don’t my child windows display correctly?
2. Ensure that the parent window is visible and child controls have the WS_VISIBLE style applied. Missing this style often causes controls to remain hidden.
3. How can I handle resizing of child windows?
4. Respond to the WM_SIZE message in the WndProc function and adjust child window positions dynamically based on the new parent dimensions.
5. Why is my button text clipped?
6. Use SendMessageW with WM_SETFONT to apply a custom font that fits the size of your button control.
7. How can I handle button click events?
8. Capture WM_COMMAND messages in the WndProc function, and use control IDs to identify which button was clicked.
9. What are some common styles for child controls?
10. Styles like WS_CHILD, WS_VISIBLE, and WS_BORDER are commonly used. Combine these as needed for specific behaviors.

Final Thoughts on Crafting Rust GUIs

Developing GUIs with the Windows API in Rust can feel overwhelming, but with a structured approach, it becomes manageable. Understanding how child windows work and paying attention to styles like WS_VISIBLE ensures your controls are displayed properly. It's all about nailing the small details! 💡

By mastering techniques such as responding to WM_COMMAND messages and dynamically resizing controls, you create a professional, responsive application. These skills, while technical, are essential for delivering polished software. Keep experimenting, and don't hesitate to debug patiently—it's worth the effort! 🚀