We welcome contributions and feedback on our website! Please file a request in our issue tracker and we'll take a look.

For simple changes (such as to CSS and text), you probably don't need to build this site. Often you can make changes using the GitHub UI.

If you want/need to build, read on.

Install the following tools if you don't have them already.

• nvm, the Node Version Manager.
• rvm, the Ruby Version Manager.
• Flutter
• Dart SDK

IMPORTANT: Follow the installation instructions for each of the tools carefully. In particular, configure your shell/environment so that the tools are available in every terminal/command window you create.

NOTE: This repo has a git submodule, which affects how you clone it.

To clone this repo, follow the instructions given in the GitHub help on Cloning a repository, and choose one of the following submodule-cloning techniques:

• Clone this repo and its submodule at the same, use the --recurse-submodules option:
  git clone --recurse-submodules https://github.com/flutter/website.git
• If you've already cloned this repo without its submodule, then run this command from the repo root:
  git submodule update --init --remote

IMPORTANT: Whenever you update your repo, update the submodule as well:
git pull; git submodule update --init --remote

NOTE: It is safe to (re-)run all of the commands and scripts given below even if you already have the required packages installed.

Open a terminal/command window and execute the following commands:

1. cd <path-to-this-repo>   # change to root of this repo
2. source ./tool/env-set.sh   # initialize environment variables; install/use required Node & Ruby version
3. ./tool/before-install.sh   # install core set of required tools
4. ./tool/install.sh   # install everything else needed to build this site

IMPORTANT:

• Any time you create a new terminal/command window to work on this repo, repeat steps 1 and 2 above.
• If you upgrade Dart then rerun all of the steps above.

1. Create a branch.

2. Make your changes.

3. Test your changes by serving the site locally. Run either one of these commands:

   • tool/serve.sh, or
   • bundle exec jekyll serve --incremental --watch --livereload --port 4002

4. Prior to submitting, run link validation:
   tool/shared/check-links.sh

For edits made directly in the GitHub web UI, the changes will be deployed to a staging site (such as https://flutter-io-deploy-three.firebaseapp.com/inspector) by the Travis job.

For edits you make locally (using the 'developing' steps above), you can deploy them to a personal staging site as follows (steps 1 and 2 need to be done only once):

1. In the Firebase Console, create your own Firebase project (e.g. 'mit-flutter-staging')

2. Tell Firebase about that project with the firebase use command:

   $ firebase use --add
   ? Which project do you want to add? <select the project you created>
   ? What alias do you want to use for this project? (e.g. staging) staging
   

3. Tell Firebase that you want to deploy to staging:

   $ firebase use staging
   Now using alias staging (<your project name>)
   

4. Tell Firebase to deploy:

   $ firebase use staging
   Now using alias staging (<your project name>)
   $ firebase deploy
   
   === Deploying to '<your project name>'...
   
   i  deploying hosting
   i  hosting: preparing _site directory for upload...
   ✔  hosting: 213 files uploaded successfully
   i  starting release process (may take several minutes)...
   
   ✔  Deploy complete!
   

(Eventually, this section should be expanded to its own page.)

If you have a document that spans multiple pages, you can add next and previous page links to make navigating these pages easier. It involves adding some information to the front matter of each page, and including some HTML.

---
layout: tutorial
title: Constraints

permalink: /tutorials/layout/constraints.html
prev-page: /tutorials/layout/properties.html
prev-page-title: "Container Properties"
next-page: /tutorials/layout/create.html
next-page-title: "Create a Layout"
---

{% include prev-next-nav.html %}

{:toc}

<!-- PAGE CONTENT -->

{% include prev-next-nav.html %}

Omit the "prev-page" info for the first page, and the "next-page" info for the last page.

The flutter.io website uses prism.js for syntax highlighting. This section covers how to use syntax highlighting, and how to update our syntax highlighter for new languages.

This website can syntax highlight the following languages:

• shell
• dart
• html
• css
• javascript
• java
• objectivec
• swift

The easiest way to syntax highlight a block of code is to wrap it with triple backticks followed by the language.

Here's an example:

```dart
class ExampleWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new Container();
  }
}
```

See the list of supported languages above for what to use following the first triple backticks.

The flutter.io website uses a custom build of prism, which includes only the languages the website requires. To improve load times and user experience, we do not support every language that prism supports.

To add a new language for syntax highlighting, you will need to generate a new copy of the prism.js file.

Follow these steps to generate a new copy of prism.js:

• Open js/prism.js
• Copy the URL in the comment of the first line of the file
• Paste it into a browser window/tab
• Add the new language that you wish to syntax highlight
• DO NOT change the other plugins, languages, or settings
• Download the generated JavaScript, and use it to replace js/prism.js
• Download the generated CSS, and use it to replace _sass/_prism.scss

Do you want to highlight (make the background yellow) code inside a code block? Do you want to strike-through code inside a code block? We got that!

For syntax highlighting, plus yellow highlighting and strike-through formatting, use the prettify tag with additional custom inline markup.

If you want to highlight a specific bit of code, use the [[highlight]]highlight this text[[/highlight]] syntax with the prettify tag.

For example:

{% prettify dart %}
void main() {
  print([[highlight]]'Hello World'[[/highlight]]);
}
{% endprettify %}

If you want to strike-through a specific bit of code, use the [[strike]]highlight this text[[/strike]] syntax with the prettify tag.

For example:

{% prettify dart %}
void main() {
  print([[strike]]'Hello World'[[/strike]]);
}
{% endprettify %}

The prettify plugin will also unindent your code.

If you want to see how this functionality was added to this site, refer to this commit.

You can include a specific range of lines from a file:

{% include includelines filename=PATH start=INT count=INT %}

PATH must be inside of _include. If you are including source code, place that code into _include/code to follow our convention.

The code snippets in the markdown documentation are validated as part of the build process. Anything within a '```dart' code fence will be extracted into its own file and checked for analysis issues. Some ways to tweak that:

• If a code snippet should not be analyzed, immediately proceed it with a <!-- skip --> comment
• To include code to be analyzed, but not displayed, add that in a comment immediately proceeding the snippet (e.g., <!-- someCodeHere(); -->)
• A snippet without any import statements will have an import ('package:flutter/material.dart') automatically added to it
• We ignore special formatting tags like [[highlight]].

The sample catalog's markdown files are generated by running sample_page.dart from the Flutter github repo. Starting from the root of the Flutter repo:

cd examples/catalog
dart bin/sample_page.dart '<commit hashcode here>'
cp examples/catalog/.generated/*.md <your website repo>/catalog/samples

The generated markdown files will contain cloud storage links for sample app screenshots. Screenshots for each sample app are automatically generated for each Flutter repo commit. Choose a recent commit hashcode and confirm that the screenshots look OK.

If new sample apps have been added, update _data/catalog/widget.json. The entry for each widget class that's featured in a sample app should contain "sample" line like:

"sample": "ListView_index",

The sample_page.dart app will print a list of all of the "sample" properties that should appear in the widget.json file.

Some form of broken links prevention is done automatically by rake checklinks on every commit (through tool/travis.sh). But this won't see any Firebase redirects (rake checklinks doesn't run the Firebase server) and it won't check incoming links.

Before we can move the more complete automated linkcheck solution from dartlang.org, we recommend manually running the following.

• First time setup:

  pub global activate linkcheck
  npm install -g superstatic
  

• Start the localhost Firebase server:

  superstatic --port 4002
  

• Run the link checker:

  linkcheck :4002
  

  Even better, to check that old URLs are correctly redirected:

  linkcheck :4002 --input-file tool/sitemap.txt