Download file by click in synchronous mode

[assopri]

Hello! I`m trying to automate scenario of downloading video from my own youtube channel:

When I click Скачать (Download) in browser the file save dialog appears. I found the solution to use here https://stackoverflow.com/questions/28565319/force-cefsharp-to-download-without-showing-dialog , but its asynchronous. What if I need to wait for download to be finished before getting to next algorithm step? So my canonical code should look like this:

Navigate();
ClickDownloadButton();
WaitForDownloadToFinish();
DoSmthWithDownloadedFile();

How could I organize this?

[amaitland]

Downloading is handled asynchronously, I personally would discourage trying to make it synchronous.

You can use the new fluent DownloadHandler implementation to simplify the process.

#3550 (comment)

There is also some new method for downloading files given a url. See https://github.com/cefsharp/CefSharp/pull/3576/files#diff-b5d302e3b07bf84e99ffa745fe37affd00a70cae3e5dd66c51911e30540c06c1R342

[assopri]

Can I somehow stop execution of the high level algorithm to wait for the download handler to finish?

[amaitland]

Stop execution of what exactly?

[assopri]

Wait (2) after click

to be sure that after WaitForDownloadToFinish returned, download is finished.

[ukandrewc]

You can use a DispatcherFrame or AutoResetEvent to wait for the download to complete.

You would initially need to wait for the OnBeforeDownload event with a timeout, because it may not be raised, if there is an error or the URL is invalid.

[amaitland]

You can use a DispatcherFrame

DispatcherFrame is intended to be used in WPF. WinForms doesn't use a dispatcher.

@assopri What exactly is your requirement to run your methods sequentially? Something like the following will be much easier to implement and avoids a number of different threading issues.

using CefSharp.Fluent;

//Save all files to temp folder, update to whatever suites you.
var userTempPath = System.IO.Path.GetTempPath();

chromiumWebBrowser.DownloadHandler =
                    DownloadHandler.UseFolder(userTempPath,
                        (chromiumBrowser, browser, downloadItem, callback) =>
                        {
                            if(downloadItem.IsComplete)
                            {
                                DoSmthWithDownloadedFile();
                            }                         
                        });

If you can obtain the url you can avoid using a download handler all together and simply directly download the file https://github.com/cefsharp/CefSharp/pull/3576/files#diff-b5d302e3b07bf84e99ffa745fe37affd00a70cae3e5dd66c51911e30540c06c1R342

[amaitland]

how can I cancel showing the separate popup form, appearing after I click on download link?

You can close the popup after the download is complete by using something like the following:

chromiumWebBrowser.DownloadHandler =
                    DownloadHandler.UseFolder(userTempPath,
                        (chromiumBrowser, browser, downloadItem, callback) =>
                        {
                            if(downloadItem.IsComplete)
                            {
                                if(browser.IsPopup && !browser.HasDocument)
				{
				  browser.GetHost().CloseBrowser(true);
				}
                            }
                        });

Because here I just set OnDownloadUpdateDelegate in this case (as 2nd parameter) instead of OnBeforeDownloadDelegate. And I cannot to anything like this:

Not sure what you are trying to do here exactly. If you are finished with the download handler instance just set the DownloadHandler to null and assign a different instance later.

browser.DownloadHandler = null;

If that's not what you mean then please provide more detail.

To make sure code more readable please use formatting as per https://docs.github.com/en/github/writing-on-github/working-with-advanced-formatting/creating-and-highlighting-code-blocks

[assopri]

how can I cancel showing the separate popup form, appearing after I click on download link?

You can close the popup after the download is complete by using something like the following:

chromiumWebBrowser.DownloadHandler =
                    DownloadHandler.UseFolder(userTempPath,
                        (chromiumBrowser, browser, downloadItem, callback) =>
                        {
                            if(downloadItem.IsComplete)
                            {
                                if(browser.IsPopup && !browser.HasDocument)
				{
				  browser.GetHost().CloseBrowser(true);
				}
                            }
                        });

Because here I just set OnDownloadUpdateDelegate in this case (as 2nd parameter) instead of OnBeforeDownloadDelegate. And I cannot to anything like this:

Not sure what you are trying to do here exactly. If you are finished with the download handler instance just set the DownloadHandler to null and assign a different instance later.

I mean, I want not to close the popup, but avoid showing it at all.

[amaitland]

I mean, I want not to close the popup, but avoid showing it at all.

To stop showing it at all then you'll need to change the behaviour of the link that initiated the download. For example remove the target="_blank" from the <a/> tag will avoid creating a popup/tab. You can probably achieve this via javascript.

The default behaviour in Chrome is to open a tab and to remove it once the download has started.

For CEF you can hide the popup once the download has started and close it once the download is complete. The popup will need to remain hidden until the download is complete, then it can be closed.

[DllImport("user32.dll")]
[return: MarshalAs(UnmanagedType.Bool)]
private static extern bool IsWindowVisible(IntPtr hWnd);

[DllImport("user32.dll")]
private static extern bool ShowWindow(IntPtr hWnd, int nCmdShow);

var tempPath = System.IO.Path.GetTempPath();

browser.DownloadHandler =
	Fluent.DownloadHandler.UseFolder(tempPath,
		(chromiumBrowser, browser, downloadItem, callback) =>
		{
			if (downloadItem.IsComplete || downloadItem.IsCancelled)
			{
				if (browser.IsPopup && !browser.HasDocument)
				{
					browser.GetHost().CloseBrowser(true);
				}
			}
			//TODO: You may wish to customise this condition to better suite your
			//requirements. 
			else if(downloadItem.ReceivedBytes < 100)
			{
				var popupHwnd = browser.GetHost().GetWindowHandle();

				var visible = IsWindowVisible(popupHwnd);
				if(visible)
				{
					const int SW_HIDE = 0;
					ShowWindow(popupHwnd, SW_HIDE);
				}
			}
		});

[assopri]

Cool! That was what I was really looking for!

[assopri]

Now I really feel happy and very excited! Thank you!!!

[ukandrewc]

Application.DoEvents() is intended to allow UI refresh. Using it in a loop to wait for another task, you also need to sleep the thread otherwise it will consume 100% processor time. That is why I suggested DispatcherFrame or ResetEvent.

I agree that downloading async is best, but that's not the question :-)