Flex（弹性布局）

Overview（概述）

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The Flexbox (or Flex for short) is a subset of CSS Flexbox.

It can arrange items into rows or columns (tracks), handle wrapping, adjust the spacing between the items and tracks, handle grow to make the item(s) fill the remaining space with respect to min/max width and height.

To make an object flex container call lv_obj_set_layout(obj, LV_LAYOUT_FLEX).

Note that the flex layout feature of LVGL needs to be globally enabled with LV_USE_FLEX in lv_conf.h.

Flexbox（弹性布局）（或简称 Flex）是 CSS Flexbox 的一个子集。

它可以将元素排列成行或列（轨道(tracks)），处理包裹，调整元素和轨道之间的间距，处理 grow 以使元素填充相对于最小/最大宽度和高度的剩余空间。

要使对象变为 flex 容器请调用 lv_obj_set_layout(obj, LV_LAYOUT_FLEX) 。

请注意，LVGL 的 flex 布局功能需要打开 lv_conf.h 中的宏 LV_USE_FLEX 启用。

Terms（约定）

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tracks: the rows or columns
main direction: row or column, the direction in which the items are placed
cross direction: perpendicular to the main direction
wrap: if there is no more space in the track a new track is started
grow: if set on an item it will grow to fill the remaining space on the track. The available space will be distributed among items respective to their grow value (larger value means more space)
gap: the space between the rows and columns or the items on a track

术语约定：

tracks（轨道）：行或列
main direction（主要方向或主轴）：行或列，元素放置的方向
cross direction（交叉方向或交叉轴）：垂直于主方向
wrap（包裹）：如果轨道中没有更多空间，则开始新的轨道放置元素
grow（增长）：如果设置在一个元素上，它将增长以填充轨道上的剩余空间。可用空间将根据其增长值分配给各个元素（值越大意味着空间越大）
gap（间隙）：行和列或轨道上的元素之间的空间

Simple interface（简单接口）

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With the following functions you can set a Flex layout on any parent.

使用以下功能，可以在任何父级上设置 Flex 布局。

Flex flow（布局流向）

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lv_obj_set_flex_flow(obj, flex_flow)

The possible values for flex_flow are:

LV_FLEX_FLOW_ROW: Place the children in a row without wrapping
LV_FLEX_FLOW_COLUMN: Place the children in a column without wrapping
LV_FLEX_FLOW_ROW_WRAP: Place the children in a row with wrapping
LV_FLEX_FLOW_COLUMN_WRAP: Place the children in a column with wrapping
LV_FLEX_FLOW_ROW_REVERSE: Place the children in a row without wrapping but in reversed order
LV_FLEX_FLOW_COLUMN_REVERSE: Place the children in a column without wrapping but in reversed order
LV_FLEX_FLOW_ROW_WRAP_REVERSE: Place the children in a row with wrapping but in reversed order
LV_FLEX_FLOW_COLUMN_WRAP_REVERSE: Place the children in a column with wrapping but in reversed order

设置接口 lv_obj_set_flex_flow(obj, flex_flow)，其中 flex_flow 的值可以是：

LV_FLEX_FLOW_ROW: 将孩子排成一排，不包裹起来
LV_FLEX_FLOW_COLUMN: 将孩子放在一列，不包裹起来
LV_FLEX_FLOW_ROW_WRAP:将孩子按行排列并包裹起来
LV_FLEX_FLOW_COLUMN_WRAP:将孩子按列排列并包裹起来
LV_FLEX_FLOW_ROW_REVERSE: 将孩子排成一排，不包裹起来，但顺序相反
LV_FLEX_FLOW_COLUMN_REVERSE: 将孩子放在一列，不包裹起来，但顺序相反
LV_FLEX_FLOW_ROW_WRAP_REVERSE: 将孩子按行排列并包裹起来，但顺序相反
LV_FLEX_FLOW_COLUMN_WRAP_REVERSE: 将孩子按列排列并包裹起来，但顺序相反

（注：flex-flow是flex-direction 与 flex-wrap的结合）

Flex align（对齐方式）

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To manage the placement of the children use lv_obj_set_flex_align(obj, main_place, cross_place, track_cross_place)

main_place determines how to distribute the items in their track on the main axis. E.g. flush the items to the right on LV_FLEX_FLOW_ROW_WRAP. (It's called justify-content in CSS)
cross_place determines how to distribute the items in their track on the cross axis. E.g. if the items have different height place them to the bottom of the track. (It's called align-items in CSS)
track_cross_place determines how to distribute the tracks (It's called align-content in CSS)

The possible values are:

LV_FLEX_ALIGN_START: means left on a horizontally and top vertically (default)
LV_FLEX_ALIGN_END: means right on a horizontally and bottom vertically
LV_FLEX_ALIGN_CENTER: simply center
LV_FLEX_ALIGN_SPACE_EVENLY: items are distributed so that the spacing between any two items (and the space to the edges) is equal. Does not apply to track_cross_place.
LV_FLEX_ALIGN_SPACE_AROUND: items are evenly distributed in the track with equal space around them. Note that visually the spaces aren't equal, since all the items have equal space on both sides. The first item will have one unit of space against the container edge, but two units of space between the next item because that next item has its own spacing that applies. Not applies to track_cross_place.
LV_FLEX_ALIGN_SPACE_BETWEEN: items are evenly distributed in the track: first item is on the start line, last item on the end line. Not applies to track_cross_place.

要管理孩子的对齐，请使用 lv_obj_set_flex_align(obj, main_place, cross_place, track_cross_place)

main_place 定义子元素在主轴方向上的对齐方式。例如。将 LV_FLEX_FLOW_ROW_WRAP 上的元素向右刷新。（它在 CSS 中称为 justify-content ）
cross_place 定义子元素在交叉轴的对齐方式。例如。如果元素具有不同的高度，则将它们放置在轨道的底部。（在 CSS 中称为 align-items ）
track_cross_place 定义多行元素在交叉轴的对齐方式（在 CSS 中称为 align-content ）

可能的值为：

LV_FLEX_ALIGN_START: 表示左侧水平，顶部垂直（默认）
LV_FLEX_ALIGN_END: 表示右侧水平，底部垂直
LV_FLEX_ALIGN_CENTER: 居中摆放
LV_FLEX_ALIGN_SPACE_EVENLY: 元素的分布使得任意两个元素之间的间距（以及到边缘的间距）相等，包括首尾元素离容器边缘的距离。不适用于 cross_place。
LV_FLEX_ALIGN_SPACE_AROUND: 元素在轨道上均匀分布，元素两侧之间的间隔相等。请注意，从视觉上看，空间并不相等，因为所有元素的两侧都有相等的空间。第一个元素在容器边缘有一个单位的空间，但下一个元素之间有两个单位的间隔，因为下一个项有自己的适用间距。不适用于 cross_place。
LV_FLEX_ALIGN_SPACE_BETWEEN: 元素在轨道上彼此之间的间隔相等，首尾元素贴合容器边缘。不适用于 cross_place。

Flex grow（弹性增长）

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Flex grow can be used to make one or more children fill the available space on the track. When more children have grow parameters, the available space will be distributed proportionally to the grow values. For example, there is 400 px remaining space and 4 objects with grow:

A with grow = 1
B with grow = 1
C with grow = 2

A and B will have 100 px size, and C will have 200 px size.

Flex grow can be set on a child with lv_obj_set_flex_grow(child, value). value needs to be > 1 or 0 to disable grow on the child.

Flex grow（弹性增长）可用于让一个或多个孩子填满轨道上的可用空间。当很多孩子都有生长参数时，可用空间将按比例分配给生长值。例如，还有400像素的剩余空间和4个带有grow的对象：

A 增长 = 1
B 增长 = 1
C 增长 = 2

A 和 B 的大小为 100 px，而 C 的大小为 200 px。

可以使用 lv_obj_set_flex_grow(child, value) 在子节点上设置 Flex 增长值。 value 需要 > 1 或 0 才能禁用在孩子身上生长。

Style interface（样式接口）

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All the Flex-related values are style properties under the hood and you can use them similarly to any other style property.

The following flex related style properties exist:

FLEX_FLOW
FLEX_MAIN_PLACE
FLEX_CROSS_PLACE
FLEX_TRACK_PLACE
FLEX_GROW

所有与 Flex 相关的值都是底层的样式属性，可以像使用任何其他样式属性一样使用它们。存在以下与 flex 相关的样式属性：

FLEX_FLOW
FLEX_MAIN_PLACE
FLEX_CROSS_PLACE
FLEX_TRACK_PLACE
FLEX_GROW

Internal padding（内部填充）

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To modify the minimum space flexbox inserts between objects, the following properties can be set on the flex container style:

pad_row Sets the padding between the rows.
pad_column Sets the padding between the columns.

These can for example be used if you don't want any padding between your objects: lv_style_set_pad_column(&row_container_style, 0)

要修改对象之间的间距，可以在 flex 容器上设置以下样式属性：

pad_row 设置行之间的内边距。
pad_column 设置列之间的内边距。

例如，如果你不希望对象之间有任何填充，可以这样设置： lv_style_set_pad_column(&row_container_style, 0)

Other features（其它功能）

RTL

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If the base direction of the container is set the LV_BASE_DIR_RTL the meaning of LV_FLEX_ALIGN_START and LV_FLEX_ALIGN_END is swapped on ROW layouts. I.e. START will mean right.

The items on ROW layouts, and tracks of COLUMN layouts will be placed from right to left.

如果容器的基本方向设置为 LV_BASE_DIR_RTL ，那么 LV_FLEX_ALIGN_START 和 LV_FLEX_ALIGN_END 的意思是在 ROW 布局上交换，START 的意思是右。

ROW 布局上的元素和 COLUMN 布局的轨道将从右向左放置。

New track（新轨道）

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You can force Flex to put an item into a new line with lv_obj_add_flag(child, LV_OBJ_FLAG_FLEX_IN_NEW_TRACK).

可以使用接口 lv_obj_add_flag(child, LV_OBJ_FLAG_FLEX_IN_NEW_TRACK) 强制 Flex 将元素放入新行。

Example

[English]

A simple row and a column layout with flexbox

#include "../../lv_examples.h"
#if LV_USE_FLEX && LV_BUILD_EXAMPLES

/**
 * A simple row and a column layout with flexbox
 */
void lv_example_flex_1(void)
{
    /*Create a container with ROW flex direction*/
    lv_obj_t * cont_row = lv_obj_create(lv_screen_active());
    lv_obj_set_size(cont_row, 300, 75);
    lv_obj_align(cont_row, LV_ALIGN_TOP_MID, 0, 5);
    lv_obj_set_flex_flow(cont_row, LV_FLEX_FLOW_ROW);

    /*Create a container with COLUMN flex direction*/
    lv_obj_t * cont_col = lv_obj_create(lv_screen_active());
    lv_obj_set_size(cont_col, 200, 150);
    lv_obj_align_to(cont_col, cont_row, LV_ALIGN_OUT_BOTTOM_MID, 0, 5);
    lv_obj_set_flex_flow(cont_col, LV_FLEX_FLOW_COLUMN);

    uint32_t i;
    for(i = 0; i < 10; i++) {
        lv_obj_t * obj;
        lv_obj_t * label;

        /*Add items to the row*/
        obj = lv_button_create(cont_row);
        lv_obj_set_size(obj, 100, LV_PCT(100));

        label = lv_label_create(obj);
        lv_label_set_text_fmt(label, "Item: %"LV_PRIu32"", i);
        lv_obj_center(label);

        /*Add items to the column*/
        obj = lv_button_create(cont_col);
        lv_obj_set_size(obj, LV_PCT(100), LV_SIZE_CONTENT);

        label = lv_label_create(obj);
        lv_label_set_text_fmt(label, "Item: %"LV_PRIu32, i);
        lv_obj_center(label);
    }
}

#endif

Arrange items in rows with wrap and even spacing

#include "../../lv_examples.h"
#if LV_USE_FLEX && LV_BUILD_EXAMPLES

/**
 * Arrange items in rows with wrap and place the items to get even space around them.
 */
void lv_example_flex_2(void)
{
    static lv_style_t style;
    lv_style_init(&style);
    lv_style_set_flex_flow(&style, LV_FLEX_FLOW_ROW_WRAP);
    lv_style_set_flex_main_place(&style, LV_FLEX_ALIGN_SPACE_EVENLY);
    lv_style_set_layout(&style, LV_LAYOUT_FLEX);

    lv_obj_t * cont = lv_obj_create(lv_screen_active());
    lv_obj_set_size(cont, 300, 220);
    lv_obj_center(cont);
    lv_obj_add_style(cont, &style, 0);

    uint32_t i;
    for(i = 0; i < 8; i++) {
        lv_obj_t * obj = lv_obj_create(cont);
        lv_obj_set_size(obj, 70, LV_SIZE_CONTENT);
        lv_obj_add_flag(obj, LV_OBJ_FLAG_CHECKABLE);

        lv_obj_t * label = lv_label_create(obj);
        lv_label_set_text_fmt(label, "%"LV_PRIu32, i);
        lv_obj_center(label);
    }
}

#endif

Demonstrate flex grow

#include "../../lv_examples.h"
#if LV_USE_FLEX && LV_BUILD_EXAMPLES

/**
 * Demonstrate flex grow.
 */
void lv_example_flex_3(void)
{
    lv_obj_t * cont = lv_obj_create(lv_screen_active());
    lv_obj_set_size(cont, 300, 220);
    lv_obj_center(cont);
    lv_obj_set_flex_flow(cont, LV_FLEX_FLOW_ROW);

    lv_obj_t * obj;
    obj = lv_obj_create(cont);
    lv_obj_set_size(obj, 40, 40);           /*Fix size*/

    obj = lv_obj_create(cont);
    lv_obj_set_height(obj, 40);
    lv_obj_set_flex_grow(obj, 1);           /*1 portion from the free space*/

    obj = lv_obj_create(cont);
    lv_obj_set_height(obj, 40);
    lv_obj_set_flex_grow(obj, 2);           /*2 portion from the free space*/

    obj = lv_obj_create(cont);
    lv_obj_set_size(obj, 40, 40);           /*Fix size. It is flushed to the right by the "grow" items*/
}

#endif

Demonstrate flex grow.

#include "../../lv_examples.h"
#if LV_USE_FLEX && LV_BUILD_EXAMPLES

/**
 * Reverse the order of flex items
 */
void lv_example_flex_4(void)
{

    lv_obj_t * cont = lv_obj_create(lv_screen_active());
    lv_obj_set_size(cont, 300, 220);
    lv_obj_center(cont);
    lv_obj_set_flex_flow(cont, LV_FLEX_FLOW_COLUMN_REVERSE);

    uint32_t i;
    for(i = 0; i < 6; i++) {
        lv_obj_t * obj = lv_obj_create(cont);
        lv_obj_set_size(obj, 100, 50);

        lv_obj_t * label = lv_label_create(obj);
        lv_label_set_text_fmt(label, "Item: %"LV_PRIu32, i);
        lv_obj_center(label);
    }
}

#endif

Demonstrate column and row gap style properties

#include "../../lv_examples.h"
#if LV_USE_FLEX && LV_BUILD_EXAMPLES

static void row_gap_anim(void * obj, int32_t v)
{
    lv_obj_set_style_pad_row(obj, v, 0);
}

static void column_gap_anim(void * obj, int32_t v)
{
    lv_obj_set_style_pad_column(obj, v, 0);
}

/**
 * Demonstrate the effect of column and row gap style properties
 */
void lv_example_flex_5(void)
{
    lv_obj_t * cont = lv_obj_create(lv_screen_active());
    lv_obj_set_size(cont, 300, 220);
    lv_obj_center(cont);
    lv_obj_set_flex_flow(cont, LV_FLEX_FLOW_ROW_WRAP);

    uint32_t i;
    for(i = 0; i < 9; i++) {
        lv_obj_t * obj = lv_obj_create(cont);
        lv_obj_set_size(obj, 70, LV_SIZE_CONTENT);

        lv_obj_t * label = lv_label_create(obj);
        lv_label_set_text_fmt(label, "%"LV_PRIu32, i);
        lv_obj_center(label);
    }

    lv_anim_t a;
    lv_anim_init(&a);
    lv_anim_set_var(&a, cont);
    lv_anim_set_values(&a, 0, 10);
    lv_anim_set_repeat_count(&a, LV_ANIM_REPEAT_INFINITE);

    lv_anim_set_exec_cb(&a, row_gap_anim);
    lv_anim_set_duration(&a, 500);
    lv_anim_set_playback_duration(&a, 500);
    lv_anim_start(&a);

    lv_anim_set_exec_cb(&a, column_gap_anim);
    lv_anim_set_duration(&a, 3000);
    lv_anim_set_playback_duration(&a, 3000);
    lv_anim_start(&a);
}

#endif

RTL base direction changes order of the items

#include "../../lv_examples.h"
#if LV_USE_FLEX && LV_BUILD_EXAMPLES

/**
 * RTL base direction changes order of the items.
 * Also demonstrate how horizontal scrolling works with RTL.
 */
void lv_example_flex_6(void)
{
    lv_obj_t * cont = lv_obj_create(lv_screen_active());
    lv_obj_set_style_base_dir(cont, LV_BASE_DIR_RTL, 0);
    lv_obj_set_size(cont, 300, 220);
    lv_obj_center(cont);
    lv_obj_set_flex_flow(cont, LV_FLEX_FLOW_ROW_WRAP);

    uint32_t i;
    for(i = 0; i < 20; i++) {
        lv_obj_t * obj = lv_obj_create(cont);
        lv_obj_set_size(obj, 70, LV_SIZE_CONTENT);

        lv_obj_t * label = lv_label_create(obj);
        lv_label_set_text_fmt(label, "%"LV_PRIu32, i);
        lv_obj_center(label);
    }
}
#endif

API

lv_flex.h