The host limits the number of templates to display for a given task to a maximum
of five, of which the last template must be one of the following types:

- [`NavigationTemplate`](https://developer.android.com/reference/androidx/car/app/navigation/model/NavigationTemplate)
- [`PaneTemplate`](https://developer.android.com/reference/androidx/car/app/model/PaneTemplate)
- [`MessageTemplate`](https://developer.android.com/reference/androidx/car/app/model/MessageTemplate)
- [`MediaPlaybackTemplate`](https://developer.android.com/reference/kotlin/androidx/car/app/media/model/MediaPlaybackTemplate)
- [`SignInTemplate`](https://developer.android.com/reference/androidx/car/app/model/signin/SignInTemplate)
- [`LongMessageTemplate`](https://developer.android.com/reference/androidx/car/app/model/LongMessageTemplate)

Note that this limit applies to the number of templates and not the number of
`Screen` instances in the stack. For example, if an app sends two templates
while in screen A and then pushes screen B, it can now send three more
templates.

Alternatively, if each screen is structured to send a single template, then the
app can push five screen instances onto the `ScreenManager` stack.

> [!CAUTION]
> **Caution:** If the template quota is exhausted and the app attempts to send a new template, the host displays an error message to the user before closing the app.

> [!NOTE]
> **Note:** During development with Android Auto, you can see the current number of steps overlaid on the screen by first enabling [Developer Mode](https://developer.android.com/training/cars/testing#developer-mode) and then checking **Enable debug overlay** in the **Developer Settings** screen. On Android Automotive OS, you can see the current number of steps in the logcat output after running `adb shell setprop log.tag.CarApp.H.Dis VERBOSE`.

There are special cases to these restrictions: template refreshes and back and
reset operations.

### Template refreshes

Certain content updates are not counted toward the template limit. In general,
if an app pushes a new template that is of the same type and contains
the same main content as the previous template, the new template is not
counted against the quota. For example, updating the toggle state of a row in a
[`ListTemplate`](https://developer.android.com/reference/androidx/car/app/model/ListTemplate) does not count against the quota. See the documentation of
individual templates to learn more about what types of content updates can be
considered a refresh.

### Back operations

To enable sub-flows within a task, the host detects when an app is popping a
`Screen` from the `ScreenManager` stack and updates the remaining quota based on
the number of templates that the app is going backward by.

For example, if the app sends two templates while in screen A, then pushes
screen B and sends two more templates, the app has one quota remaining. If
the app then pops back to screen A, the host resets the quota to three, because
the app has gone backward by two templates.

Note that, when popping back to a screen, an app must send a template that is
of the same type as the one last sent by that screen. Sending any other
template type causes an error. However, as long as the type remains the
same during a back operation, an app can freely modify the contents of the
template without affecting the quota.

### Reset operations

Certain templates have special semantics that signify the end of a task. For
example, the [`NavigationTemplate`](https://developer.android.com/reference/androidx/car/app/navigation/model/NavigationTemplate) is a view that's expected to remain on
the screen and be refreshed with new turn-by-turn instructions for the user.

When a task reaches one of these templates, the host resets the
template quota, treating that template as though it's the first step of a new
task. This allows the app to start a new task. To learn more, see the
documentation for individual templates to learn which trigger a reset on the
host.

If the host receives an intent to start the app from a notification action or
from the launcher, the quota is also reset. This mechanism lets an app
begin a new task flow from notifications, and it holds true even if an app is
already bound and in the foreground.