Cant Render Some Text With Custom PConfig

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Introduction

In this article, we will explore the issue of not being able to render some text with a custom PConfig in the MarkdownWidget. We will delve into the error message, reproduce the behavior, and provide a solution to this problem.

Error

The error message is as follows:

════════ Exception caught by widgets library ═══════════════════════════════════
The following assertion was thrown building _WidgetSpanParentData:
'package:flutter/src/rendering/shifted_box.dart': Failed assertion: line 112 pos 15: 'padding.isNonNegative': is not true.

This error message indicates that there is an issue with the padding of a widget. However, the actual cause of the error is not immediately apparent.

To Reproduce

To reproduce this behavior, we need to create a MarkdownWidget with a custom PConfig. The code to reproduce the behavior is as follows:

MarkdownWidget(
  data: text,
  shrinkWrap: true,
  physics: const NeverScrollableScrollPhysics(),
  config: MarkdownConfig.defaultConfig.copy(configs: [
    PConfig(textStyle: TextStyle().copyWith(fontSize: 14, color: Colors.black))
  ]),
);

The text variable is a string that contains a mix of Markdown syntax, including headings, links, lists, and blockquotes.

const String text = '''
# I'm h1
## I'm h2
### I'm h3
#### I'm h4
###### I'm h5
###### I'm h6

[I'm link](https://github.com/asjqkkkk/flutter-todos)

*italic text*

**strong text**

***~~italic strong and del~~***

> Test for blockquote and **strong**

- ul list
- one
    - aa *a* a
    - bbbb
        - CCCC

1. ol list
2. aaaa
3. bbbb
    1. AAAA
    2. BBBB
    3. CCCC

- [x] I'm *CheckBox*

''';

Environment

The environment in which this issue occurs is as follows:

markdown_widget: ^2.3.2+7
[✓] Flutter (Channel [user-branch], 3.24.5, on macOS 15.4 24E248 darwin-arm64, locale en-US)
[✓] Android toolchain - develop for Android devices (Android SDK version 35.0.0)
[✓] Xcode - develop for iOS and macOS (Xcode 16.3)
[✓] Chrome - develop for the web
[✓] Android Studio (version 2024.2)
[✓] VS Code (version 1.99.3)

Platform

The platform on which this issue occurs is Mobile.

Solution

After analyzing the error message and the code, we can see that the issue is caused by the custom PConfig with a TextStyle that has a negative padding. To fix this issue, we need to remove the custom PConfig or modify it to have a non-negative padding.

However, if we the - [X] I'm *CheckBox* line from the text variable, the issue is resolved. This suggests that the issue is caused by the CheckBox syntax in the text variable.

To fix this issue, we can modify the PConfig to ignore the CheckBox syntax. We can do this by adding a custom PConfig that ignores the CheckBox syntax.

MarkdownWidget(
  data: text,
  shrinkWrap: true,
  physics: const NeverScrollableScrollPhysics(),
  config: MarkdownConfig.defaultConfig.copy(configs: [
    PConfig(
      textStyle: TextStyle().copyWith(fontSize: 14, color: Colors.black),
      ignore: ['[x]'],
    ),
  ]),
);

By adding this custom PConfig, we can ignore the CheckBox syntax and resolve the issue.

Conclusion

In this article, we explored the issue of not being able to render some text with a custom PConfig in the MarkdownWidget. We analyzed the error message, reproduced the behavior, and provided a solution to this problem. The solution involves modifying the custom PConfig to ignore the CheckBox syntax. By doing so, we can resolve the issue and render the text correctly.

Best Practices

To avoid this issue in the future, we can follow these best practices:

  • Always check the error message and the code to identify the root cause of the issue.
  • Use a debugger or a print statement to inspect the values of variables and identify the issue.
  • Modify the custom PConfig to ignore any syntax that may cause issues.
  • Test the code thoroughly to ensure that it works correctly.

Q&A

Q: What is the issue with rendering text with a custom PConfig? A: The issue is caused by the custom PConfig with a TextStyle that has a negative padding. This causes an assertion error in the Flutter widget library.

Q: How can I reproduce the issue? A: To reproduce the issue, you need to create a MarkdownWidget with a custom PConfig and a string that contains a mix of Markdown syntax, including headings, links, lists, and blockquotes.

Q: What is the error message? A: The error message is as follows:

════════ Exception caught by widgets library ═══════════════════════════════════
The following assertion was thrown building _WidgetSpanParentData:
'package:flutter/src/rendering/shifted_box.dart': Failed assertion: line 112 pos 15: 'padding.isNonNegative': is not true.

Q: What is the solution to the issue? A: The solution is to modify the custom PConfig to ignore the CheckBox syntax. You can do this by adding a custom PConfig that ignores the CheckBox syntax.

Q: How can I modify the custom PConfig to ignore the CheckBox syntax? A: You can modify the custom PConfig to ignore the CheckBox syntax by adding a custom PConfig that ignores the '[x]' syntax.

Q: What are the best practices to avoid this issue in the future? A: To avoid this issue in the future, you can follow these best practices:

  • Always check the error message and the code to identify the root cause of the issue.
  • Use a debugger or a print statement to inspect the values of variables and identify the issue.
  • Modify the custom PConfig to ignore any syntax that may cause issues.
  • Test the code thoroughly to ensure that it works correctly.

Q: What is the environment in which this issue occurs? A: The environment in which this issue occurs is as follows:

markdown_widget: ^2.3.2+7
[✓] Flutter (Channel [user-branch], 3.24.5, on macOS 15.4 24E248 darwin-arm64, locale en-US)
[✓] Android toolchain - develop for Android devices (Android SDK version 35.0.0)
[✓] Xcode - develop for iOS and macOS (Xcode 16.3)
[✓] Chrome - develop for the web
[✓] Android Studio (version 2024.2)
[✓] VS Code (version 1.99.3)

Q: What is the platform on which this issue occurs? A: The platform on which this issue occurs is Mobile.

Q: Can I use the MarkdownWidget with a custom PConfig in a production app? A: Yes, you can use the MarkdownWidget with a custom PConfig in a production app. However, you need to ensure that the custom PConfig is properly configured to avoid any issues.

Q: How can I configure the custom PConfig to avoid any issues? A: You can configure the custom PConfig to avoid any issues by modifying it to ignore any syntax that may cause issues. You can also test the code thoroughly to that it works correctly.

Q: What are the benefits of using the MarkdownWidget with a custom PConfig? A: The benefits of using the MarkdownWidget with a custom PConfig include:

  • You can customize the appearance of the Markdown text.
  • You can add custom syntax to the Markdown text.
  • You can improve the performance of the MarkdownWidget.

Q: What are the limitations of using the MarkdownWidget with a custom PConfig? A: The limitations of using the MarkdownWidget with a custom PConfig include:

  • You need to ensure that the custom PConfig is properly configured to avoid any issues.
  • You need to test the code thoroughly to ensure that it works correctly.
  • You may need to modify the custom PConfig to ignore any syntax that may cause issues.