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106 lines
4.5 KiB
Markdown
106 lines
4.5 KiB
Markdown
2 years ago
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# Drop-down list (lv_dropdown)
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## Overview
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The drop-down list allows the user to select one value from a list.
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The drop-down list is closed by default and displays a single value or a predefined text.
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When activated (by click on the drop-down list), a list is created from which the user may select one option.
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When the user selects a new value, the list is deleted again.
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The Drop-down list is added to the default group (if it is set). Besides the Drop-down list is an editable object to allow selecting an option with encoder navigation too.
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## Parts and Styles
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The Dropdown widget is built from the elements: "button" and "list" (both not related to the button and list widgets)
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### Button
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- `LV_PART_MAIN` The background of the button. Uses the typical background properties and text properties for the text on it.
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- `LV_PART_INDICATOR` Typically an arrow symbol that can be an image or a text (`LV_SYMBOL`).
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The button goes to `LV_STATE_CHECKED` when it's opened.
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### List
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- `LV_PART_MAIN` The list itself. Uses the typical background properties. `max_height` can be used to limit the height of the list.
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- `LV_PART_SCROLLBAR` The scrollbar background, border, shadow properties and width (for its own width) and right padding for the spacing on the right.
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- `LV_PART_SELECTED` Refers to the currently pressed, checked or pressed+checked option. Also uses the typical background properties.
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The list is hidden/shown on open/close. To add styles to it use `lv_dropdown_get_list(dropdown)` to get the list object. For example:
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```c
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lv_obj_t * list = lv_dropdown_get_list(dropdown) /*Get the list*/
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lv_obj_add_style(list, &my_style, ...) /*Add the styles to the list*/}`
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```
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Alternatively the theme can be extended with the new styles.
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## Usage
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## Overview
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### Set options
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Options are passed to the drop-down list as a string with `lv_dropdown_set_options(dropdown, options)`. Options should be separated by `\n`. For example: `"First\nSecond\nThird"`. This string will be saved in the drop-down list, so it can in a local variable.
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The `lv_dropdown_add_option(dropdown, "New option", pos)` function inserts a new option to `pos` index.
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To save memory the options can set from a static(constant) string too with `lv_dropdown_set_static_options(dropdown, options)`.
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In this case the options string should be alive while the drop-down list exists and `lv_dropdown_add_option` can't be used
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You can select an option manually with `lv_dropdown_set_selected(dropdown, id)`, where `id` is the index of an option.
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### Get selected option
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The get the *index* of the selected option, use `lv_dropdown_get_selected(dropdown)`.
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`lv_dropdown_get_selected_str(dropdown, buf, buf_size)` copies the *name* of the selected option to `buf`.
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### Direction
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The list can be created on any side. The default `LV_DIR_BOTTOM` can be modified by `lv_dropdown_set_dir(dropdown, LV_DIR_LEFT/RIGHT/UP/BOTTOM)` function.
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If the list would be vertically out of the screen, it will be aligned to the edge.
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### Symbol
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A symbol (typically an arrow) can be added to the dropdown list with `lv_dropdown_set_symbol(dropdown, LV_SYMBOL_...)`
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If the direction of the drop-down list is `LV_DIR_LEFT` the symbol will be shown on the left, otherwise on the right.
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### Show selected
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The main part can either show the selected option or a static text. If a static is set with `lv_dropdown_set_text(dropdown, "Some text")` it will be shown regardless to th selected option.
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If the text is `NULL` the selected option is displayed on the button.
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### Manually open/close
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To manually open or close the drop-down list the `lv_dropdown_open/close(dropdown)` function can be used.
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## Events
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Apart from the [Generic events](../overview/event.html#generic-events), the following [Special events](../overview/event.html#special-events) are sent by the drop-down list:
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- `LV_EVENT_VALUE_CHANGED` Sent when the new option is selected or the list is opened/closed.
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- `LV_EVENT_CANCEL` Sent when the list is closed
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- `LV_EVENT_READY` Sent when the list is opened
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See the events of the [Base object](/widgets/obj) too.
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Learn more about [Events](/overview/event).
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## Keys
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- `LV_KEY_RIGHT/DOWN` Select the next option.
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- `LV_KEY_LEFT/UP` Select the previous option.
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- `LY_KEY_ENTER` Apply the selected option (Sends `LV_EVENT_VALUE_CHANGED` event and closes the drop-down list).
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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:: ../../../examples/widgets/dropdown/index.rst
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```
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## API
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```eval_rst
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.. doxygenfile:: lv_dropdown.h
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:project: lvgl
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```
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