System.Windows.Forms.WebBrowser wait until page has been fully loaded

问题

I have been trying a lot of different solutions with wait and async. Nothing seems to work. I was not able to find solution that actually fully waits until page has been fully loaded. All codes are waiting some time but not until page has been loaded and I am getting an error on next process.

How I can set for example code into wait mode until Document.GetElementById("quickFind_text_0") element has been found on page?

Here is my code:

    private void button7_Click(object sender, EventArgs e)
    {

        webBrowser1.Navigate("https://company.crm4.dynamics.com/main.aspx?app=d365default&pagetype=entitylist&etn=opportunity");

        webBrowser1.Document.GetElementById("shell-container").Document.GetElementById("quickFind_text_0").SetAttribute("value", "Airbus");

        webBrowser1.Document.GetElementById("shell-container").Document.GetElementById("quickFind_text_0").InnerText = "Airbus";

        //Thread.Sleep(2000);

        HtmlElement fbLink = webBrowser1.Document.GetElementById("shell-container").Document.GetElementById("mainContent").Document.GetElementById("quickFind_button_0"); ;
        fbLink.InvokeMember("click");
    }

P.S. I have to do this "twice" otherwise it is not working:

    webBrowser1.Document.GetElementById("shell-container").Document.GetElementById("quickFind_text_0").SetAttribute("value", "Airbus");

    webBrowser1.Document.GetElementById("shell-container").Document.GetElementById("quickFind_text_0").InnerText = "Airbus";

In VBA this works:

    While .Busy
        DoEvents

    Wend
    While .ReadyState <> 4
        DoEvents
    Wend

Is it possible to do the same in C#?

---

EDIT:

My full code below. For some reason async/await does not work.

System.NullReferenceException HResult=0x80004003 Message=Object reference not set to an instance of an object. Source=v.0.0.01
StackTrace: at v._0._0._01.Browser.d__7.MoveNext() in C:\Users\PC\source\repos\v.0.0.01\v.0.0.01\Browser.cs:line 69

Here is my code:

using System;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace v.0._0._01
{

    public static class WebBrowserExtensions
    {
        public static Task<Uri> DocumentCompletedAsync(this WebBrowser wb)
        {
            var tcs = new TaskCompletionSource<Uri>();
            WebBrowserDocumentCompletedEventHandler handler = null;
            handler = (_, e) =>
            {
                wb.DocumentCompleted -= handler;
                tcs.TrySetResult(e.Url);
            };
            wb.DocumentCompleted += handler;
            return tcs.Task;
        }
    }

    public partial class Browser : Form
    {

        public Browser()
        {
            InitializeComponent();
        }

        private async void button7_Click(object sender, EventArgs e)
        {

            webBrowser1.Navigate("https://company.crm4.dynamics.com/main.aspx?app=d365default&pagetype=entitylist&etn=opportunity");
            await webBrowser1.DocumentCompletedAsync(); // async magic
            HtmlElement fbLink = webBrowser1.Document.GetElementById("shell-container").Document.GetElementById("mainContent").Document.GetElementById("quickFind_button_0"); ;
            fbLink.InvokeMember("click");

        }

    }

}

Here is the source code:

Also now I have noticed that quickFind_text_0 and quickFind_button_0 always starts with same words but numbers are changing like quickFind_text_1 and quickFind_button_1 or quickFind_text_2 and quickFind_button_2. However by manual clicking everything works with quickFind_text_0 and quickFind_button_0.

回答1:

Here is an extension method for easy awaiting of the DocumentCompleted event:

public static class WebBrowserExtensions
{
    public static Task<Uri> DocumentCompletedAsync(this WebBrowser wb)
    {
        var tcs = new TaskCompletionSource<Uri>();
        WebBrowserDocumentCompletedEventHandler handler = null;
        handler = (_, e) =>
        {
            wb.DocumentCompleted -= handler;
            tcs.TrySetResult(e.Url);
        };
        wb.DocumentCompleted += handler;
        return tcs.Task;
    }
}

It can be used like this:

private async void button1_Click(object sender, EventArgs e)
{

    webBrowser1.Navigate("https://company.crm4.dynamics.com/main.aspx");
    await webBrowser1.DocumentCompletedAsync(); // async magic
    HtmlElement fbLink = webBrowser1.Document.GetElementById("quickFind_button_0");
    fbLink.InvokeMember("click");
}

The lines after the await will run after the page has completed loading.

---

Update: Here is another extension method for awaiting a specific element to appear in the page:

public static async Task<HtmlElement> WaitForElementAsync(this WebBrowser wb,
    string elementId, int timeout = 30000, int interval = 500)
{
    var stopwatch = Stopwatch.StartNew();
    while (true)
    {
        try
        {
            var element = wb.Document.GetElementById(elementId);
            if (element != null) return element;
        }
        catch { }
        if (stopwatch.ElapsedMilliseconds > timeout) throw new TimeoutException();
        await Task.Delay(interval);
    }
}

It can be used for example after invoking a click event that modifies the page using XMLHttpRequest:

someButton.InvokeMember("click");
var mainContentElement = await webBrowser1.WaitForElementAsync("mainContent", 5000);

来源：https://stackoverflow.com/questions/59473425/system-windows-forms-webbrowser-wait-until-page-has-been-fully-loaded