83 lines
2.7 KiB
Markdown
83 lines
2.7 KiB
Markdown
```eval_rst
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.. include:: /header.rst
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:github_url: |github_link_base|/widgets/btn.md
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```
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# Button (lv_btn)
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## Overview
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Buttons are simple rectangle-like objects. They are derived from [Containers](/widgets/cont) so [layout](/widgets/cont#layout) and [fit](/widgets/cont#fit) are also available.
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Besides, it can be enabled to automatically go to checked state on click.
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## Parts and Styles
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The buttons has only a main style called `LV_BTN_PART_MAIN` and it can use all the properties from the following groups:
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- background
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- border
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- outline
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- shadow
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- value
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- pattern
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- transitions
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It also uses the *padding* properties when *layout* or *fit* is enabled.
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## Usage
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### States
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To make buttons usage simpler the button's state can be get with `lv_btn_get_state(btn)`. It returns one of the following values:
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- **LV_BTN_STATE_RELEASED**
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- **LV_BTN_STATE_PRESSED**
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- **LV_BTN_STATE_CHECKED_RELEASED**
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- **LV_BTN_STATE_CHECKED_PRESSED**
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- **LV_BTN_STATE_DISABLED**
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- **LV_BTN_STATE_CHECKED_DISABLED**
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With `lv_btn_set_state(btn, LV_BTN_STATE_...)` the buttons state can be changed manually.
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If a more precise description of the state is required (e.g. focused) the general `lv_obj_get_state(btn)` can be used.
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### Checkable
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You can configure the buttons as *toggle button* with `lv_btn_set_checkable(btn, true)`. In this case, on click, the button goes to `LV_STATE_CHECKED` state automatically, or back when clicked again.
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### Layout and Fit
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Similarly to [Containers](/widgets/cont), buttons also have layout and fit attributes.
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- `lv_btn_set_layout(btn, LV_LAYOUT_...) `set a layout. The default is `LV_LAYOUT_CENTER`.
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So, if you add a label, then it will be automatically aligned to the middle and can't be moved with `lv_obj_set_pos()`.
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You can disable the layout with `lv_btn_set_layout(btn, LV_LAYOUT_OFF)`.
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- `lv_btn_set_fit/fit2/fit4(btn, LV_FIT_..)` enables to set the button width and/or height automatically according to the children, parent, and fit type.
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## Events
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Besides the [Generic events](../overview/event.html#generic-events) the following [Special events](../overview/event.html#special-events) are sent by the buttons:
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- **LV_EVENT_VALUE_CHANGED** - sent when the button is toggled.
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Learn more about [Events](/overview/event).
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## Keys
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The following *Keys* are processed by the Buttons:
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- **LV_KEY_RIGHT/UP** - Go to toggled state if toggling is enabled.
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- **LV_KEY_LEFT/DOWN** - Go to non-toggled state if toggling is enabled.
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Note that, the state of `LV_KEY_ENTER` is translated to `LV_EVENT_PRESSED/PRESSING/RELEASED` etc.
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Learn more about [Keys](/overview/indev).
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## Example
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```eval_rst
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.. include:: /lv_examples/src/lv_ex_widgets/lv_ex_btn/index.rst
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```
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## API
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```eval_rst
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.. doxygenfile:: lv_btn.h
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:project: lvgl
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```
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