LegacyProject/ScreenSaverEf/PreviewForm.cs

using System;
using System.Drawing;
using System.Runtime.InteropServices;
using System.Windows.Forms;

namespace ScreenSaverEf
{
    public partial class PreviewForm : Form
    {
        [DllImport("user32.dll")]
        private static extern IntPtr SetParent(IntPtr hWndChild, IntPtr hWndNewParent);

        [DllImport("user32.dll")]
        private static extern bool GetClientRect(IntPtr hWnd, out Rectangle lpRect);

        public PreviewForm(IntPtr hWndParent)
        {
            InitializeComponent();

            SetParent(this.Handle, hWndParent);//设置屏保预览窗口为FrmControl的父窗口

            GetClientRect(hWndParent, out var parentRect);

            this.Location = new Point(0, 0);

            this.Size = parentRect.Size;
        }
    }
}