WebView on iOS cann't download file

[weedcry]

Description

I am using the webview on iOS to load a URL. I want to download a file using the webview, but when I try to download it, the webview just open it without downloading

Steps to Reproduce

1. Load webview with url ( https://file-examples.com/index.php/sample-documents-download/sample-pdf-download/ )
2. slip down and click DOWNLOAD SAMPLE PDF FILE

Link to public reproduction project repository

https://github.com/dotnet/maui/files/11550334/WebviewExample.zip

Version with bug

7.0.49

Last version that worked well

Unknown/Other

Affected platforms

iOS

Affected platform versions

iOS 16.2

Did you find any workaround?

I haven't found

Relevant log output

No response

[ghost]

Hi @weedcry. We have added the "s/needs-info" label to this issue, which indicates that we have an open question for you before we can take further action. This issue will be closed automatically in 7 days if we do not hear back from you by then - please feel free to re-open it if you come back to this issue after that time.

[rachelkang]

Hi, @weedcry - Are you seeing this working on Android or any other platform? The behavior you're describing sounds like it may be what is expected

[weedcry]

Hi, @weedcry - Are you seeing this working on Android or any other platform? The behavior you're describing sounds like it may be what is expected

Hi @rachelkang
On the Windows platform, it is possible to download some files when clicking on the download button. On the Android platform, it seems to be similar to iOS, but after handling the OnDownloadStart event, it is possible to download the file.
I have just found a way to download files on iOS by handling the DecideDestination event of the WKDownloadDelegate, but I still cannot save the file.

[weedcry]

I tried to save the file using the path obtained through the following method. However, I received an error with "The operation couldn’t be completed. (NSURLErrorDomain error -3000.)". Can anyone help me?

public override void DecideDestination(WKDownload download, NSUrlResponse response, string suggestedFilename, Action<NSUrl> completionHandler)
{
	var fileManager = NSFileManager.DefaultManager;
	var documentDirectory = fileManager.GetUrls(NSSearchPathDirectory.DocumentDirectory, NSSearchPathDomain.User)[0];
	var fileUrl = documentDirectory.Append(suggestedFilename, false);
	completionHandler(fileUrl);
}

public override void DidFinish(WKDownload download)
{	
}

public override void DidFail(WKDownload download, NSError error, NSData? resumeData)
{
}

[weedcry]

I tried to save the file using the path obtained through the following method. However, I received an error with "The operation couldn’t be completed. (NSURLErrorDomain error -3000.)". Can anyone help me?

public override void DecideDestination(WKDownload download, NSUrlResponse response, string suggestedFilename, Action<NSUrl> completionHandler)
{
	var fileManager = NSFileManager.DefaultManager;
	var documentDirectory = fileManager.GetUrls(NSSearchPathDirectory.DocumentDirectory, NSSearchPathDomain.User)[0];
	var fileUrl = documentDirectory.Append(suggestedFilename, false);
	completionHandler(fileUrl);
}

public override void DidFinish(WKDownload download)
{	
}

public override void DidFail(WKDownload download, NSError error, NSData? resumeData)
{
}

I have solved the issue above. But I can only save the file to the data of a third-party app.

var fileManager = NSFileManager.DefaultManager;
var documentDirectory = fileManager.GetUrls(NSSearchPathDirectory.DocumentDirectory, NSSearchPathDomain.All)[0];

I want to save the file to the Downloads folder of iOS but I can't figure out how to get its path.

[drasticactions]

This is not a MAUI bug. This is the default behavior of WebView on iOS/Catalyst. As the MAUI WebView cross-platform interface doesn't have a strict way of handling downloads beyond what the WebViews on the platforms themselves do, IMO, it's not a bug in MAUI, but a feature that would need to be added if we wanted something like that. As such, I've moved this to a discussion:

As you've seen, the default behavior is to show it inside the webview, and you have to add the handlers to the underlying WKWebView to change that. This is a pain to do in Swift/ObjC and needs to be better documented there, and it's worse for C#/Xamarin.

https://github.com/drasticactions/MauiRepros/tree/main/WebviewTestCatalyst2

I've implemented a solution that should work. You need to implement IWKDownloadDelegate and IWKNavigationDelegate and override the default response to show the PDF inside of the page

public class TestDownloadWebView : WKWebView, IWKDownloadDelegate, IWKNavigationDelegate
    {
        public TestDownloadWebView(CGRect frame, WKWebViewConfiguration configuration) : base(frame, configuration)
        {
            this.NavigationDelegate = this;
        }

        public void DecideDestination(WKDownload download, NSUrlResponse response, string suggestedFilename,
            Action<NSUrl> completionHandler)
        {
            var destinationURL = GetDestinationURL();

            completionHandler?.Invoke(destinationURL);
        }

        [Export("webView:decidePolicyForNavigationResponse:decisionHandler:")]
        public void DecidePolicy(WKWebView webView, WKNavigationResponse navigationResponse, Action<WKNavigationResponsePolicy> decisionHandler)
        {
            var url = navigationResponse.Response.Url;
            var mimeType = navigationResponse.Response.MimeType;
            Console.WriteLine($"Content-Type: {mimeType}");

            // Perform any actions based on the content type
            if (mimeType == "application/pdf")
            {
                // Download the PDF file separately instead of loading it in the WKWebView
                DownloadPDF(url);

                decisionHandler?.Invoke(WKNavigationResponsePolicy.Cancel);
            }
            else
            {
                decisionHandler?.Invoke(WKNavigationResponsePolicy.Allow);
            }
           
        }

        private void DownloadPDF(NSUrl url)
        {
            var downloadTask = NSUrlSession.SharedSession.CreateDownloadTask(url, (location, _, error) =>
            {
                if (location is NSUrl sourceURL && error == null)
                {
                    var destinationURL = GetDestinationURL();

                    try
                    {
                        NSFileManager.DefaultManager.Move(sourceURL, destinationURL, out error);
                        Console.WriteLine($"PDF file downloaded and saved at: {destinationURL.Path}");

                        // Perform any additional actions with the downloaded file
                    }
                    catch (Exception ex)
                    {
                        // Handle file moving error
                    }
                }
                else
                {
                    // Handle download error
                }
            });

            downloadTask.Resume();
        }

        private NSUrl GetDestinationURL()
        {
            // Customize the destination URL as desired
            var documentsURL =
                NSFileManager.DefaultManager.GetUrls(NSSearchPathDirectory.DocumentDirectory, NSSearchPathDomain.User)
                    [0];
            var destinationURL = documentsURL.Append("downloaded_file.pdf", false);

            return destinationURL;
        }
    }

There are other ways beyond this one that should work as well. This has more to do with the weird APIs of WKWebView than anything specific in MAUI. Again, unless there is some kind of new API introduced to MAUI for how to handle downloads of WebViews, it's going to be onto whatever the platform view itself does, which results in weird stuff like this.