const int CS_DROPSHADOW = 0x20000;

        constint GCL_STYLE = (-26);

        //声明Win32 API

        [DllImport("user32.dll", CharSet = CharSet.Auto)]

        publicstatic extern int SetClassLong(IntPtrhwnd, int nIndex, intdwNewLong);

        [DllImport("user32.dll", CharSet = CharSet.Auto)]

        public static extern int GetClassLong(IntPtrhwnd, int nIndex);

//调用

SetClassLong(this.Handle, GCL_STYLE, GetClassLong(this.Handle, GCL_STYLE) | CS_DROPSHADOW);

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