Скачать или смотреть Fixing WebView.EvaluateJavascript Not Calling OnReceiveValue in Xamarin.Android

Learn how to solve the issue with `WebView.EvaluateJavascript` not consistently calling `OnReceiveValue` in Xamarin.Android. Follow our step-by-step guide to implement a custom `WebViewClient` effectively.
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This video is based on the question https://stackoverflow.com/q/63241467/ asked by the user 'Raphnika' ( https://stackoverflow.com/u/6701068/ ) and on the answer https://stackoverflow.com/a/63242053/ provided by the user 'Leo Zhu' ( https://stackoverflow.com/u/10768653/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Troubleshooting WebView.EvaluateJavascript in Xamarin.Android

When venturing into Xamarin.Android development, you've likely encountered common challenges related to WebView. A frequent issue developers face is when WebView.EvaluateJavascript unpredictably fails to call the OnReceiveValue method of the callback class. If you're struggling with this, you're not alone! In this guide, we’ll explore the problem and how to effectively address it.

Understanding the Problem

You may find that despite the implementation of the JavascriptResult class, the OnReceiveValue method is not invoked consistently. This can lead to a frustrating experience, especially when you need to fetch and manipulate web content dynamically. Below is an example of an existing implementation:

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In the above code, the intention is to retrieve the HTML content from a webpage, but the callback doesn't always function as expected.

The Solution: Custom WebViewClient

To resolve this issue, the recommended approach is to create a custom WebViewClient and call EvaluateJavascript within the OnPageFinished method. This ensures that the JavaScript evaluation occurs after the page has fully loaded, which is critical for accessing the DOM elements you want.

Here’s How to Implement This Solution

Modify the GetHtmlContent Method: Adjust your existing method to include the custom WebViewClient.

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Create the Custom MyClient Class: Inside your class, implement a WebViewClient that overrides the OnPageFinished method.

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Benefits of This Approach

Ensured Execution Timing: By placing the EvaluateJavascript call in OnPageFinished, you guarantee that it executes only after the webpage is fully loaded.

Reliable Data Retrieval: With the new implementation, you enhance the reliability of fetching the HTML content, leading to fewer instances of OnReceiveValue being overlooked.

Conclusion

By following these steps to implement a custom WebViewClient, you can solve the persistent issue of WebView.EvaluateJavascript not calling OnReceiveValue. This adjustment not only optimizes your code but also ensures a smoother user experience in your Xamarin.Android applications.

If you have any further questions or need additional assistance, feel free to leave a comment below. Happy coding!