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Understand the Xamarin.Forms architecture first
The official EVO Xamarin integration installs two pieces: a client library in the platform project and an EVO PDF Server installed separately. The server performs navigation, resource loading, rendering, and PDF generation; the mobile application sends it conversion work. The Xamarin documentation specifically discusses iOS, Android, and macOS integrations, so treat Xamarin.Forms as a shared UI layer over one of those platform projects. Verify that the package and native runtime support your actual target before debugging conversion settings.
A phone’s 127.0.0.1 is the phone itself, not your development computer. In an emulator, loopback may refer to the emulator, a host alias, or a virtual network depending on the platform. Test the configured address from the environment in which the client code actually runs.
Use a repeatable diagnostic sequence
- Save the complete exception and response. Record whether it fails while opening the server connection, navigating, loading a resource, executing JavaScript, writing the PDF, or applying a license.
- Identify the binary actually loaded. In Visual Studio’s project references and build output, record the NuGet package, assembly name, namespace, and version. The legacy API reference names
EvoPdf.HtmlToPdfClient, assemblyEvoHtmlToPdfClient.dll, version 9.0.0.0; the Xamarin example usesEvoPdfClient. Do not mix examples from those API generations. - Record deployment facts. Note the platform (Android, iOS, or macOS), the machine running EVO PDF Server, its listening port, any service password or web-service URL, and the address configured in the app.
- Reduce the input. Convert a plain HTML string with inline text. Then test a simple public URL, add an external stylesheet and image, and finally restore scripts, authentication, and application data one change at a time.
- Keep a minimal reproduction. If the failure remains, provide EVO support the exact package version, target platform, server version, address, port, HTML, and exception.
Fix “Could not connect to server IP 127.0.0.1 on port 40001”
EVO’s troubleshooting guide says this message means the EVO PDF Server is not installed or is not accessible at the TCP/IP address configured in the client. Check the following in order:
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- Install the EVO PDF Server on the intended machine and confirm its service or executable is running.
- Confirm that the client is using the server’s reachable LAN address or host name, not an accidental device-local loopback address.
- Verify that the configured port is the port on which the server listens. Port
40001in the exception is evidence of the attempted destination, not proof that every EVO installation uses that port. - Allow the port through the server machine’s firewall and any cloud, VPN, corporate, or emulator network policy between client and server.
- From the runtime environment, test route and DNS resolution. A desktop browser reaching the server does not prove that a phone or simulator can reach it.
- If using EVO’s web-service deployment rather than a local TCP service, check the configured service URL and authentication settings instead of troubleshooting a local socket.
Only after a minimal HTML conversion reaches the server should you investigate CSS, images, JavaScript, or page layout.
Repair missing CSS, fonts, and images
Give relative URLs a base
An HTML string containing <link href="css/site.css"> or <img src="images/logo.png"> has no meaningful origin unless you provide one. Pass a base URL through the API version you installed, or change references to absolute, server-reachable URLs. A file path such as C:assetslogo.png is not automatically a valid browser URL; use the URL format and permissions expected by that EVO version.
Check access from the server, not only from the app
The PDF Server fetches external resources. Test the stylesheet, image, font, and API URLs from the server machine. Private resources may require custom headers, cookies, a service account, VPN access, or an allow-list entry. A resource visible in the mobile app can still be unreachable to the server.
Separate resource failure from CSS failure
Start with inline CSS and a data-free image. If that works, add one external resource at a time. Inspect HTTP redirects, TLS certificates, 401/403 responses, and mixed-content rules. For an HTML string generated inside the app session, preserve a base URL even when the markup itself is complete; linked assets still need an origin.
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Correct text or image size that looks smaller than the HTML
PDF layout is a page-size calculation, not a screenshot at the browser’s CSS pixel width. The legacy HtmlToPdfConverter reference documents a default HtmlViewerWidth of 1024 pixels. Its troubleshooting guide suggests trying approximately 800 pixels for A4 portrait output or disabling FitWidth. Those are version-specific settings and a trial, not universal values.
- Set the intended paper size and orientation before judging scale.
- Compare output with and without fit-to-page scaling.
- Try a narrower viewer width when a desktop-width page is being reduced to A4.
- Use CSS media rules deliberately; print CSS can change font sizes, widths, and visibility.
- Check whether a newer rendering engine has different defaults. EVO’s release notes describe EVO PDF Next v14.75 as scaling a 1024-pixel browser window to a fixed A4 page, but that does not establish the defaults of a legacy Xamarin package.
Do not copy a property name from a different assembly. Confirm that your referenced version exposes HtmlViewerWidth and FitWidth, then inspect the generated PDF at 100-percent zoom rather than comparing screen pixels.
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Make JavaScript and AJAX content appear
Use a delay when load time is predictable
Client-side rendering, API calls, charts, and lazy components may finish after the initial document load. The legacy API reference lists ConversionDelay with a documented default of two seconds. Increase it only when the page needs more time, and keep the value matched to the installed API.
Use a readiness signal when load time varies
A fixed delay can be wasteful or still too short. A more reliable design is to have the page signal that required content is ready, then trigger conversion manually through the option provided by your EVO version. This avoids capturing an intermediate state when network latency changes.
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For pages with no asynchronous work, EVO documents an automatic mode or a zero delay to avoid an unnecessary pause. Do not set zero until you have ruled out deferred scripts, AJAX, image lazy-loading, and web fonts.
The legacy API reference lists a 60-second NavigationTimeout default. A timeout is not proof that JavaScript failed: distinguish a slow server, an unreachable API, an infinite script, and a page that never signaled readiness.
Handle ASP.NET session-authenticated pages
EVO explains that conversion executes the page in a new session, different from the ASP.NET application’s session. Cookies and server-side session values available to the app therefore may not exist in the conversion request.
When the page depends on those values, generate the final HTML inside the authenticated application session, intercept the rendered markup, and convert that string. Supply a correct base URL for every relative stylesheet, image, font, or script reference. This approach preserves the session-derived content while still requiring the conversion server to reach its linked resources.
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| Approach | Use when | Watch for |
|---|---|---|
| Convert a URL | The page is publicly reachable or the converter can be given all required authentication context. | Separate converter session, redirects, cookies, and server-side network access. |
| Convert generated HTML | Markup depends on the current app session or private values. | Correct base URL, accessible linked assets, and safe handling of user data. |
Eliminate the demo warning or watermark
A watermark usually indicates that a demo key is still active somewhere in the conversion path. Set the purchased key on every relevant converter or document object, including objects created in helper methods, and search the solution for code that later assigns a demo key. Confirm that the licensed assembly is deployed with the app and that the key is applied before conversion. If only one screen is watermarked, compare its object construction with a screen that is not.
Keep API names and versions aligned
The legacy namespace EvoPdf.HtmlToPdfClient and assembly EvoHtmlToPdfClient.dll version 9.0.0.0 are not interchangeable with the EvoPdfClient namespace shown in the Xamarin sample. EVO’s release notes identify EVO PDF Next v14.75, but a release-note version is not evidence that an older Xamarin client can use its defaults or methods.
For each build, record:
- the NuGet package ID and resolved version;
- the assembly loaded at runtime;
- the namespace and constructor used;
- the server product and version;
- the Xamarin platform project that performs the call.
If a property or method is missing, stop adapting a snippet from another generation. Open the documentation matching the referenced assembly or contact EVO with the complete version pair.
A version-conscious Xamarin.Forms test harness
Use a tiny service so networking and conversion can be tested independently of page navigation. The exact constructor and conversion method differ between EVO client generations; select them from the documentation shipped with your referenced package rather than combining the names below with another assembly.
public async Task<byte[]> ConvertDiagnosticHtmlAsync()
{
const string html = "<html><body><h1>EVO test</h1><p>Static content</p></body></html>";
// Create the HtmlToPdfConverter using the constructor documented
// for the Evo package referenced by this platform project.
// Configure the server host, port, license key, page size and timeout there.
// Then convert this inline HTML before adding URLs or JavaScript.
throw new NotSupportedException("Bind this call to the API version installed in the platform project.");
}This deliberately fails at compile time until you bind the version-matched constructor; it prevents a copied legacy sample from silently targeting the wrong API. Once the static test succeeds, add a base URL, then one external image, then scripts and authentication. Keep the successful static case as a regression test.
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Troubleshooting checklist by symptom
| Symptom | First check | Likely correction |
|---|---|---|
| Connection refused or timeout | Server state, host, port, firewall, route | Install/start EVO PDF Server and use an address reachable from the app runtime. |
| HTML text appears but CSS or images do not | Relative URLs and server-side fetch access | Provide a base URL or absolute URLs; fix permissions, authentication, redirects, or certificates. |
| Everything is too small | Viewer width, fit scaling, paper size | Test the version-matched width and fit settings; the legacy guide suggests about 800 pixels as a trial. |
| Charts or AJAX are absent | Readiness timing and API reachability | Use an appropriate delay or manual trigger; verify the converter can reach data endpoints. |
| Private page loses data | Separate conversion session | Render HTML inside the app session and convert the resulting string with a valid base URL. |
| Demo watermark remains | All key assignments and object creation paths | Apply the purchased key to every relevant object and remove later demo-key assignments. |
| Compile errors after copying a sample | Namespace, assembly, package and version | Use documentation for the exact dependency loaded by the platform project. |
When to contact EVO support
Contact the vendor after the minimal inline conversion, server reachability check, and version audit. Include the exact exception text, target platform, client assembly and version, server version, configured endpoint, firewall result, reduced HTML, and whether the failure occurs before or after navigation. EVO’s support information distinguishes evaluation inquiries, so identify an evaluation request when that applies. No published success rate or performance benchmark establishes how quickly a particular configuration should convert; measure your own pages after correctness is established.
Frequently Asked Questions
Does Xamarin.Forms itself run the EVO rendering engine?
No. The app references an EVO client library while the separately installed EVO PDF Server performs conversion. The relevant iOS, Android, or macOS platform project must support the package you selected.
Is port 40001 required for every EVO installation?
No. It is the destination shown in one common error. Verify the listening port in your server configuration and use the address reachable from the device or emulator.
Should I always increase the conversion delay?
No. Use a delay only when asynchronous content needs it. For variable load times, a page-controlled readiness trigger is more reliable; static pages can use the documented automatic or zero-delay mode.
Why does converting an HTML string still lose images?
An HTML string can still contain relative references. Supply the correct base URL and confirm that the EVO PDF Server—not just the mobile app—can fetch each asset.
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