using System;
using System.Windows.Forms;

namespace WebBrowserExample
{
    public partial class Form1 : Form
    {
        private string viewStateValue;

        public Form1()
        {
            InitializeComponent();
            webBrowser1.DocumentCompleted += WebBrowser1_DocumentCompleted;
            webBrowser1.Navigate("https://your-target-url.com");
        }

        private void WebBrowser1_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
        {
            // 確保網頁已經加載完成
            if (webBrowser1.ReadyState == WebBrowserReadyState.Complete)
            {
                // 獲取 __VIEWSTATE
                var viewStateElement = webBrowser1.Document.GetElementById("__VIEWSTATE");
                if (viewStateElement != null)
                {
                    viewStateValue = viewStateElement.GetAttribute("value");
                    MessageBox.Show("獲取到的 VIEWSTATE: " + viewStateValue);
                    
                    // 設置新的 __VIEWSTATE 值
                    SetViewState(viewStateValue);
                }
                else
                {
                    MessageBox.Show("__VIEWSTATE 元素未找到。");
                }
            }
        }

        private void SetViewState(string newViewState)
        {
            // 使用 JavaScript 設置 __VIEWSTATE 的值
            string script = $"document.getElementById('__VIEWSTATE').value = '{newViewState}';";
            webBrowser1.Document.InvokeScript("eval", new object[] { script });

            // 你可以在這裡進行其他操作，比如提交表單
            // webBrowser1.Document.GetElementById("submitButton").InvokeMember("click");
        }
    }
}