ndg/lib/lvgl/docs/widgets/core/label.md

Label (lv_label)

Overview

A label is the basic object type that is used to display text.

Parts and Styles

• LV_PART_MAIN Uses all the typical background properties and the text properties. The padding values can be used to add space between the text and the background.
• LV_PART_SCROLLBAR The scrollbar that is shown when the text is larger than the widget's size.
• LV_PART_SELECTED Tells the style of the selected text. Only text_color and bg_color style properties can be used.

Usage

Set text

You can set the text on a label at runtime with lv_label_set_text(label, "New text"). This will allocate a buffer dynamically, and the provided string will be copied into that buffer. Therefore, you don't need to keep the text you pass to lv_label_set_text in scope after that function returns.

With lv_label_set_text_fmt(label, "Value: %d", 15) printf formatting can be used to set the text.

Labels are able to show text from a static character buffer. To do so, use lv_label_set_text_static(label, "Text"). In this case, the text is not stored in the dynamic memory and the given buffer is used directly instead. This means that the array can't be a local variable which goes out of scope when the function exits. Constant strings are safe to use with lv_label_set_text_static (except when used with LV_LABEL_LONG_DOT, as it modifies the buffer in-place), as they are stored in ROM memory, which is always accessible.

Newline

Newline characters are handled automatically by the label object. You can use \n to make a line break. For example: "line1\nline2\n\nline4"

Long modes

By default, the width and height of the label is set to LV_SIZE_CONTENT. Therefore, the size of the label is automatically expanded to the text size. Otherwise, if the width or height are explicitly set (using e.g.lv_obj_set_width or a layout), the lines wider than the label's width can be manipulated according to several long mode policies. Similarly, the policies can be applied if the height of the text is greater than the height of the label.

• LV_LABEL_LONG_WRAP Wrap too long lines. If the height is LV_SIZE_CONTENT the label's height will be expanded, otherwise the text will be clipped. (Default)
• LV_LABEL_LONG_DOT Replaces the last 3 characters from bottom right corner of the label with dots (.)
• LV_LABEL_LONG_SCROLL If the text is wider than the label scroll it horizontally back and forth. If it's higher, scroll vertically. Only one direction is scrolled and horizontal scrolling has higher precedence.
• LV_LABEL_LONG_SCROLL_CIRCULAR If the text is wider than the label scroll it horizontally continuously. If it's higher, scroll vertically. Only one direction is scrolled and horizontal scrolling has higher precedence.
• LV_LABEL_LONG_CLIP Simply clip the parts of the text outside the label.

You can specify the long mode with lv_label_set_long_mode(label, LV_LABEL_LONG_...)

Note that LV_LABEL_LONG_DOT manipulates the text buffer in-place in order to add/remove the dots. When lv_label_set_text or lv_label_set_array_text are used, a separate buffer is allocated and this implementation detail is unnoticed. This is not the case with lv_label_set_text_static. The buffer you pass to lv_label_set_text_static must be writable if you plan to use LV_LABEL_LONG_DOT.

Text recolor

In the text, you can use commands to recolor parts of the text. For example: "Write a #ff0000 red# word". This feature can be enabled individually for each label by lv_label_set_recolor() function.

Text selection

If enabled by LV_LABEL_TEXT_SELECTION part of the text can be selected. It's similar to when you use your mouse on a PC to select a text. The whole mechanism (click and select the text as you drag your finger/mouse) is implemented in Text area and the Label widget only allows manual text selection with lv_label_get_text_selection_start(label, start_char_index) and lv_label_get_text_selection_start(label, end_char_index).

Very long texts

LVGL can efficiently handle very long (e.g. > 40k characters) labels by saving some extra data (~12 bytes) to speed up drawing. To enable this feature, set LV_LABEL_LONG_TXT_HINT 1 in lv_conf.h.

Custom scrolling animations

Some aspects of the scrolling animations in long modes LV_LABEL_LONG_SCROLL and LV_LABEL_LONG_SCROLL_CIRCULAR can be customized by setting the animation property of a style, using lv_style_set_anim(). Currently, only the start and repeat delay of the circular scrolling animation can be customized. If you need to customize another aspect of the scrolling animation, feel free to open an issue on Github to request the feature.

Symbols

The labels can display symbols alongside letters (or on their own). Read the Font section to learn more about the symbols.

Events

No special events are sent by the Label.

See the events of the Base object too.

Learn more about Events.

Keys

No Keys are processed by the object type.

Learn more about Keys.

Example

.. include:: ../../../examples/widgets/label/index.rst

API

.. doxygenfile:: lv_label.h
  :project: lvgl