WinForms添加模糊效果的窗口设置Maximized后无法正常最大化

问题原因 #

1. 构造函数属性执行顺序错误：InitializeComponent() 是加载设计器配置（包括你设置的 WindowState = Maximized）的核心方法，你将自定义样式、边框设置、透明度配置放在了它的前后错误位置，设计器配置会覆盖你提前设置的自定义属性，导致窗口状态不符合预期。
2. 无边框窗口最大化默认预留边距：WinForms 无边框窗口设置为最大化时，系统会默认预留原窗口边框的约8px边距，这是系统内置的兼容逻辑，就是你看到的左上角空白区域。

修复方案 #

按以下步骤调整代码即可：

• 把InitializeComponent()移到构造函数第一行，确保设计器配置先加载，再应用自定义属性
• 重写WndProc方法处理WM_GETMINMAXINFO消息，移除最大化时的默认边距
• 把EnableBlur调用移到窗口句柄初始化完成之后执行，避免句柄未就绪导致效果失效

修正后完整代码

using System.Runtime.InteropServices;

namespace WF4
{
    public partial class Form1 : Form
    {
        // 处理最大化消息需要的API常量
        private const int WM_GETMINMAXINFO = 0x0024;
        
        public Form1()
        {
            // 设计器配置必须第一行加载
            InitializeComponent();
            
            // 基础样式配置
            SetStyle(ControlStyles.UserPaint, true);
            SetStyle(ControlStyles.OptimizedDoubleBuffer, true);
            SetStyle(ControlStyles.SupportsTransparentBackColor, true);
            BackColor = Color.LimeGreen;
            TransparencyKey = Color.LimeGreen;
            FormBorderStyle = FormBorderStyle.None;
            WindowState = FormWindowState.Maximized;
        }

        protected override void OnHandleCreated(EventArgs e)
        {
            base.OnHandleCreated(e);
            // 句柄创建完成后再启用模糊效果
            this.EnableBlur();
        }

        // 重写消息处理，移除最大化默认边距
        protected override void WndProc(ref Message m)
        {
            if (m.Msg == WM_GETMINMAXINFO)
            {
                MINMAXINFO mmi = (MINMAXINFO)Marshal.PtrToStructure(m.LParam, typeof(MINMAXINFO));
                // 设置最大化尺寸为当前屏幕的完整尺寸
                Screen currentScreen = Screen.FromHandle(this.Handle);
                Rectangle workingArea = currentScreen.Bounds;
                mmi.ptMaxPosition.X = workingArea.Left;
                mmi.ptMaxPosition.Y = workingArea.Top;
                mmi.ptMaxSize.X = workingArea.Width;
                mmi.ptMaxSize.Y = workingArea.Height;
                Marshal.StructureToPtr(mmi, m.LParam, true);
            }
            base.WndProc(ref m);
        }

        private void Form1_Load(object sender, EventArgs e)
        {

        }

        private void Form1_KeyDown(object sender, KeyEventArgs e)
        {
            if (e.KeyCode == Keys.Enter)
            {
                MessageBox.Show("Hllo");
            }
        }

        // 定义WM_GETMINMAXINFO需要的结构体
        [StructLayout(LayoutKind.Sequential)]
        public struct POINT
        {
            public int X;
            public int Y;
        }

        [StructLayout(LayoutKind.Sequential)]
        public struct MINMAXINFO
        {
            public POINT ptReserved;
            public POINT ptMaxSize;
            public POINT ptMaxPosition;
            public POINT ptMinTrackSize;
            public POINT ptMaxTrackSize;
        }
    }
    public static class WindowExtension
    {
        [DllImport("user32.dll")]
        static internal extern int SetWindowCompositionAttribute(IntPtr hwnd, ref WindowCompositionAttributeData data);

        public static void EnableBlur(this Form @this)
        {
            var accent = new AccentPolicy();
            accent.AccentState = AccentState.ACCENT_ENABLE_BLURBEHIND;
            var accentStructSize = Marshal.SizeOf(accent);
            var accentPtr = Marshal.AllocHGlobal(accentStructSize);
            Marshal.StructureToPtr(accent, accentPtr, false);
            var Data = new WindowCompositionAttributeData();
            Data.Attribute = WindowCompositionAttribute.WCA_ACCENT_POLICY;
            Data.SizeOfData = accentStructSize;
            Data.Data = accentPtr;
            SetWindowCompositionAttribute(@this.Handle, ref Data);
            Marshal.FreeHGlobal(accentPtr);
        }

    }
    enum AccentState
    {
        ACCENT_DISABLED = 0,
        ACCENT_ENABLE_GRADIENT = 1,
        ACCENT_ENABLE_TRANSPARENTGRADIENT = 2,
        ACCENT_ENABLE_BLURBEHIND = 3,
        ACCENT_INVALID_STATE = 4
    }

    struct AccentPolicy
    {
        public AccentState AccentState;
        public int AccentFlags;
        public int GradientColor;
        public int AnimationId;
    }

    struct WindowCompositionAttributeData
    {
        public WindowCompositionAttribute Attribute;
        public IntPtr Data;
        public int SizeOfData;
    }

    enum WindowCompositionAttribute
    {
        WCA_ACCENT_POLICY = 19
    }
}

内容的提问来源于stack exchange，提问作者Extorc Productions