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159 lines
6.1 KiB
ReStructuredText
159 lines
6.1 KiB
ReStructuredText
Label (lv_label)
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================
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Overview
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********
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A label is the basic object type that is used to display text.
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Parts and Styles
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****************
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- :cpp:enumerator:`LV_PART_MAIN` Uses all the typical background properties and the
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text properties. The padding values can be used to add space between
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the text and the background.
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- :cpp:enumerator:`LV_PART_SCROLLBAR` The scrollbar that is shown when the text is
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larger than the widget's size.
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- :cpp:enumerator:`LV_PART_SELECTED` Tells the style of the `selected
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text <#text-selection>`__. Only ``text_color`` and ``bg_color`` style
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properties can be used.
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Usage
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*****
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Set text
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--------
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You can set the text on a label at runtime with
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:cpp:expr:`lv_label_set_text(label, "New text")`. This will allocate a buffer
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dynamically, and the provided string will be copied into that buffer.
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Therefore, you don't need to keep the text you pass to
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:cpp:func:`lv_label_set_text` in scope after that function returns.
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With :cpp:expr:`lv_label_set_text_fmt(label, "Value: %d", 15)` printf formatting
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can be used to set the text.
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Labels are able to show text from a static character buffer. To do so,
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use :cpp:expr:`lv_label_set_text_static(label, "Text")`. In this case, the text
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is not stored in the dynamic memory and the given buffer is used
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directly instead. This means that the array can't be a local variable
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which goes out of scope when the function exits. Constant strings are
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safe to use with :cpp:func:`lv_label_set_text_static` (except when used with
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:cpp:enumerator:`LV_LABEL_LONG_DOT`, as it modifies the buffer in-place), as they are
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stored in ROM memory, which is always accessible.
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Newline
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-------
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Newline characters are handled automatically by the label object. You
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can use ``\n`` to make a line break. For example:
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``"line1\nline2\n\nline4"``
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Long modes
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----------
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By default, the width and height of the label is set to
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:c:macro:`LV_SIZE_CONTENT`. Therefore, the size of the label is automatically
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expanded to the text size. Otherwise, if the width or height are
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explicitly set (using e.g.\ :cpp:func:`lv_obj_set_width` or a layout), the lines
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wider than the label's width can be manipulated according to several
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long mode policies. Similarly, the policies can be applied if the height
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of the text is greater than the height of the label.
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- :cpp:enumerator:`LV_LABEL_LONG_WRAP` Wrap too long lines. If the height is :c:macro:`LV_SIZE_CONTENT` the label's
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height will be expanded, otherwise the text will be clipped. (Default)
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- :cpp:enumerator:`LV_LABEL_LONG_DOT` Replaces the last 3 characters from bottom right corner of the label with dots (``.``)
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- :cpp:enumerator:`LV_LABEL_LONG_SCROLL` If the text is wider than the label scroll it horizontally back and forth. If it's
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higher, scroll vertically. Only one direction is scrolled and horizontal scrolling has higher precedence.
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- :cpp:enumerator:`LV_LABEL_LONG_SCROLL_CIRCULAR` If the text is wider than the label scroll it horizontally continuously. If it's
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higher, scroll vertically. Only one direction is scrolled and horizontal scrolling has higher precedence.
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- :cpp:enumerator:`LV_LABEL_LONG_CLIP` Simply clip the parts of the text outside the label.
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You can specify the long mode with :cpp:expr:`lv_label_set_long_mode(label, LV_LABEL_LONG_...)`
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Note that :cpp:enumerator:`LV_LABEL_LONG_DOT` manipulates the text buffer in-place in
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order to add/remove the dots. When :cpp:func:`lv_label_set_text` or
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:cpp:func:`lv_label_set_array_text` are used, a separate buffer is allocated and
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this implementation detail is unnoticed. This is not the case with
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:cpp:func:`lv_label_set_text_static`. The buffer you pass to
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:cpp:func:`lv_label_set_text_static` must be writable if you plan to use
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:cpp:enumerator:`LV_LABEL_LONG_DOT`.
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Text recolor
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------------
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In the text, you can use commands to recolor parts of the text. For
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example: ``"Write a #ff0000 red# word"``. This feature can be enabled
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individually for each label by :cpp:func:`lv_label_set_recolor` function.
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Text selection
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--------------
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If enabled by :c:macro:`LV_LABEL_TEXT_SELECTION` part of the text can be
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selected. It's similar to when you use your mouse on a PC to select a
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text. The whole mechanism (click and select the text as you drag your
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finger/mouse) is implemented in `Text area </widgets/textarea>`__ and
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the Label widget only allows manual text selection with
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:cpp:expr:`lv_label_get_text_selection_start(label, start_char_index)` and
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:cpp:expr:`lv_label_get_text_selection_start(label, end_char_index)`.
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Text alignment
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--------------
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To horizontally align the lines of a label the `text_align` style property can be used with
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:cpp:expr:`lv_obj_set_style_text_align()` or :cpp:expr:`lv_style_set_text_align()`
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Note that it has a visible effect only if
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- the label widget's width is larger than the width of the longest line of the text
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- the text has multiple lines with non equal line length
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Very long texts
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---------------
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LVGL can efficiently handle very long (e.g. > 40k characters) labels by
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saving some extra data (~12 bytes) to speed up drawing. To enable this
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feature, set ``LV_LABEL_LONG_TXT_HINT 1`` in ``lv_conf.h``.
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Custom scrolling animations
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---------------------------
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Some aspects of the scrolling animations in long modes
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:cpp:enumerator:`LV_LABEL_LONG_SCROLL` and :cpp:enumerator:`LV_LABEL_LONG_SCROLL_CIRCULAR` can be
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customized by setting the animation property of a style, using
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:cpp:func:`lv_style_set_anim`. Currently, only the start and repeat delay of
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the circular scrolling animation can be customized. If you need to
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customize another aspect of the scrolling animation, feel free to open
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an `issue on Github <https://github.com/lvgl/lvgl/issues>`__ to request
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the feature.
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Symbols
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-------
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The labels can display symbols alongside letters (or on their own). Read
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the `Font </overview/font>`__ section to learn more about the symbols.
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Events
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******
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No special events are sent by the Label.
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See the events of the `Base object </widgets/obj>`__ too.
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Learn more about :ref:`events`.
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Keys
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****
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No *Keys* are processed by the object type.
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Learn more about :ref:`indev_keys`.
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Example
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*******
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.. include:: ../examples/widgets/label/index.rst
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API
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***
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