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Bring back access app state (#14258) 

* Recreated the access_app_state file

* Update the site's TOC to include the file

* Update code sample file path

* Minor formatting update

Co-authored-by: Jirka Borovec <Borda@users.noreply.github.com>
Co-authored-by: Sherin Thomas <sherin@grid.ai>
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Laverne Henderson 2022-08-23 10:06:46 -07:00 committed by GitHub
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docs/source-app/index.rst
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@ -216,6 +216,7 @@ Keep Learning
:maxdepth: 1
:caption: How to...
Access the App State <workflows/access_app_state/access_app_state>
Add a web user interface (UI) <workflows/add_web_ui/index>
Add a web link <workflows/add_web_link>
Arrange app tabs <workflows/arrange_tabs/index>

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docs/source-app/workflows/access_app_state/access_app_state.rst Normal file
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.. _access_app_state:
################
Access App State
################
**Audience:** Users who want to know how the App State can be accessed.
**Level:** Basic
**********************
What is the App State?
**********************
In Lightning, each component is stateful and their state is composed of all attributes defined within their **__init__** method.
The **App State** is the collection of all the components' states forming the App.
************************************
What is special about the App State?
************************************
The **App State** is always up-to-date, even running an App in the cloud on multiple machines.
This means that every time an attribute is modified in a Work, that information is automatically
broadcasted to the Flow. With this mechanism, any Component can **react** to any other
Component's **state changes** through the Flow and complex systems can be easily implemented.
Lightning requires a state based driven mindset when implementing the Flow.
***************************************
When do I need to access the App State?
***************************************
As a user, you are interacting with your component attributes, so most likely,
you won't need to access the Component's state directly, but it can be helpful to
understand how the state works under the hood.
For example, here we define a **Flow** component and **Work** component, where the Work increments a counter indefinitely and the Flow prints its state which contains the Work.
You can easily check the state of your entire App as follows:
.. literalinclude:: ../../code_samples/quickstart/app_01.py
Run the App with:
.. code-block:: bash
lightning run app docs/quickstart/app_01.py
And here's the output you get when running the App using **Lightning CLI**:
.. code-block:: console
INFO: Your app has started. View it in your browser: http://127.0.0.1:7501/view
State: {'works': {'w': {'vars': {'counter': 1}}}}
State: {'works': {'w': {'vars': {'counter': 2}}}}
State: {'works': {'w': {'vars': {'counter': 3}}}}
State: {'works': {'w': {'vars': {'counter': 3}}}}
State: {'works': {'w': {'vars': {'counter': 4}}}}
...