Version: Next

React Native Development Considerations

Taro 3 requires version 3.1 or higher

React Native's styles are based on the open source cross-platform layout engine Yoga , which basically implements a subset of CSS, and the property names are not identical, so when you start thinking about compatibility with the React Native side, you can take a brief look at A quick look at React Native styles. React Native Layout Props

Style layout on H5 is the most flexible, the next mini program, RN is the strongest, unified style that is aligned with the short board, that is, to manage the style with the constraints of RN, while taking into account the limitations of the mini program, the core can be summarized in three points.

Layout with Flex
Writing styles based on BEM
Overriding component styles with the style attribute

一、Layout

flex

Flexbox rules are used in React Native to specify the layout of a component's child elements. flexbox can provide a consistent layout structure across screen sizes. So if you're thinking about the React Native, then your style layout will have to be a Flex layout.

For an introduction to Flex layouts, check out ruanyifeng Flex Layout Tutorial: Syntax

Note: The default orientation of the View tag in RN is column. If you don't change the other ends to be consistent with RN, you need to explicitly declare the orientation of the main axis in all places where display: flex is used.

position

In React Native position only supports two properties, relative (default) and absolute. You can see the documentation

二、Styles

Selectors

Only class selectors are supported on the React Native side, and combinators are not supported Combinators and groups of selectors。

The following selectors are written in a way that they are not supported and will be automatically ignored during style conversions.

.button.button_theme_islands {
  font-style: bold;
}

img + p {
  font-style: bold;
}

p ~ span {
  color: red;
}

div > span {
  background-color: DodgerBlue;
}

div span {
  background-color: DodgerBlue;
}

If we develop based on a pre-compiled language such as scss, we can write styles based on BEM eg:

<View className="block">
    <Text className="block__elem">Text</Text>
</View>

.block: {
    background-color: DodgerBlue;
    &__elem {
        color: yellow;
    }
}

Conditional compilation of styles

1.3+ Versions Supported

Conditional compilation of style files

Suppose the following files exist in the directory at the same time.

- index.scss
- index.rn.scss

When referencing a style file in a JS file: import '. /index.scss', the RN platform will find and introduce index.rn.scss, and other platforms will introduce: index.scss, which is convenient for you to write cross-end style and better compatible with RN.

Conditional compilation of style code

To make it easier to write style code across styles, the style conditional compilation feature has been added.

Designated platform reserved:

/*  #ifdef  %PLATFORM%  */
style code
/*  #endif  */

Designated platform exclusion.

/*  #ifndef  %PLATFORM%  */
style code
/*  #endif  */

Multiple platforms can be separated by spaces.

Global introduction of styles

1. The style introduced in the entry file app.js is the global style, and the local style will override the global style.
1. Global injection through configuration

// config/index.js
...
const config = {
    ...
    sass: {
        resource: [
            'src/styles/common.scss'
        ]
    }
}

三、Navigation

React Native Navigation is encapsulated in React-Navigation 5.x. To better facilitate business customization, the configuration of React Navigation is passed through in the global and page configuration, but note that the following navigation-related settings Taro 3.x are in effect.

Global Configuration

A separate configuration for rn navigation can be added in the global configuration app.config.js

// To have an impact on the other side, it is better to add environmental judgments

let rnConfig = {}

if(process.env.TARO_ENV === 'rn'){
  rnConfig = {
  //deep Linking perfix, https://reactnavigation.org/docs/deep-linking
  linking:[],
  //tabBar page config ，https://reactnavigation.org/docs/bottom-tab-navigator/#tabbar options config，the following property pass-through is supported, and the scheme that returns the react.Node node settings is not supported
   options:{
      title，
      tabBarVisible，
      tabBarBadge，
      tabBarBadgeStyle，
      tabBarTestID
   },
   tabBarOptions:{//tabbarOptions config ,other see https://reactnavigation.org/docs/bottom-tab-navigator/#tabbar tabBarOptions
       
   },
   screenOptions:{//Global screenOptions， which works on non-all pages, note that it does not support returning React. For more references https://reactnavigation.org/docs/stack-navigator/#options
       
   }
  }
}

export default {
  pages:[
    'pages/index/index',
  ],
  rn:rnConfig
}

Page Config

In addition to the global settings page, you can also set up a page individually.

// page config
rn:{
  screenOptions:{// set curernt page options，For more references https://reactnavigation.org/docs/stack-navigator/#options
        
    }
}

There are some things to note about the configuration of pass-through react navigation.
Directly passing in parameters of React.Node nodes is not supported
The style object passed in is a React Native style such as tabStyle:{ backgroundColor :'#ff0000'}
rn's configuration takes precedence over other configurations, e.g. if the selectedColor is configured in the unified tabBar and activeTintColor in rn's configuration, then the activeTintColor is the one that takes effect

Frequently Asked Questions

1. Can box-shadow be implemented?

React Native doesn't support this well (only ios supports it and to a limited extent), and the only way to set the gray shadows on the android side is through elevation.

{
    /* Shadow related properties */
    shadowOffset: {width: 0, height: 5},
    shadowOpacity: 0.5,
    shadowRadius: 5,
    shadowColor: Color.CMHeaderBgColor,
    /* android gray shadows */
    elevation: 4,
}

2、border{Top,Right,Bottom,Left} not supported ?

The shorthand for border{Top,Right,Bottom,Left} (shorthands) is not supported, because borderStyle cannot be applied to a single border.

Use sass：

/**
 * // NOTE Taro has a problem with border handling when compiling to RN
 * RN does not support setting style for one side, i.e. border-bottom-style will report an error.
 * Then border-bottom: 1px would need to be written as follows.
 * border: 0 style color; border-bottom-width: 1px;
 */
@mixin border($dir, $width, $style, $color) {
  border: 0 $style $color;
  @each $d in $dir {
    #{border-#{$d}-width}: $width;
  }
}

3. React Native doesn't support background-image, is there any solution?s

Using the Image component, in conjunction with the Flex/Position layout, will basically accomplish most of your needs. Read this article.Background Images in React Native

Support for each property

React Native's styles are based on the open source cross-platform layout engine Yoga, The style is basically a subset of CSS, but the property names are not identical, so check the documentation for details and differences React Native Layout Props。

Text （18）

Property Name	Value	Description
color	<color>	Corresponds to `CSS` color property
fontFamily	string	Corresponds to `CSS` font-family property
fontSize	<number>	Corresponds to `CSS` font-size property
fontStyle	`normal`, `italic`	对应 `CSS` font-style 属性，但阉割了 `oblique` 取值
fontWeight	`normal`, `bold` `100~900`	Corresponds to `CSS` font-weight property，But the `bolder, lighter` fetch is neutered
lineHeight	<number>	Corresponds to `CSS` line-height property
textAlign	`auto`, `left`, `right`, `center`, `justify`^iOS	Corresponds to `CSS` text-align property,Added `auto` fetch value. When the value is `justify`, it will change to `left` on `Android`.
textDecorationLine	`none`, `underline`, `line-through`, `underline line-through`	Corresponds to `CSS` text-decoration-line property，But the `bolder, lighter` fetch is neutered
textShadowColor	<color>	Corresponds to `CSS` text-shadow the color definition in the properties
textShadowOffset	{ width:<number>, height:<number> }	Corresponds to `CSS` text-shadow shadow offset definition in the properties
textShadowRadius	<number>	In `CSS`, the size of the rounded corners of the shadow depends on the element's rounded corner definition and does not need to be defined additionally
includeFontPadding ^Android	<bool>	By default, Android reserves some extra padding for text to allow room for superscript or subscript text. For some fonts, this extra padding may make it difficult to center the text vertically. If you set `textAlignVertical` to `center` and the text still looks off-center, try setting this property to `false`.
textAlignVertical ^Android	`auto`, `top`, `bottom`, `center`	Corresponds to `CSS` vertical-align property, Added `auto` fetch, `center` replaces `middle`, and neutered `baseline, sub` and other values
fontVariant ^iOS	`small-caps`, `oldstyle-nums`, `lining-nums`, `tabular-nums`, `proportional-nums`	Corresponds to `CSS` font-variant property, but which has more values
letterSpacing ^iOS	<number>	Corresponds to `CSS` letter-spacing property
textDecorationColor ^iOS	<color>	Corresponds to `CSS` text-decoration-color property
textDecorationStyle ^iOS	`solid`, `double`, `dotted`, `dashed`	Corresponds to `CSS` text-decoration-style propery, But the `wavy` fetch is neutered
writingDirection ^iOS	`auto`, `ltr`, `rtl`	Corresponds to `CSS` direction propery, Added `auto` fetch value

Dimension (6)

Propery Name	Values	Description
width	<number>	Corresponds to `CSS` width propery
minWidth	<number>	Corresponds to `CSS` min-width propery
maxWidth	<number>	Corresponds to `CSS` max-width propery
height	<number>	Corresponds to `CSS` height propery
minHeight	<number>	Corresponds to `CSS` min-height propery
maxHeight	<number>	Corresponds to `CSS` max-height propery

Positioning （6）

Propery Name	Values	Description
position	`absolute`, `relative`	Corresponds to `CSS` position propery, but without the `static, fixed` fetch
top	<number>	Corresponds to `CSS` top propery
right	<number>	Corresponds to `CSS` right propery
bottom	<number>	Corresponds to `CSS` bottom propery
left	<number>	Corresponds to `CSS` left propery
zIndex	<number>	Corresponds to `CSS` z-index propery

Margin（7）

Propery Name	Values	Description
margin	<number>	Corresponds to `CSS` margin property, the difference is that it can only define one parameter, if you want to define the external white of `top, right, bottom and left` 4 directions respectively, you can use the following one-way external white property
marginHorizontal	<number>	No corresponding `CSS` property. The effect is equivalent to setting both `marginRight` and `marginLeft`
marginVertical	<number>	No corresponding `CSS` property. The effect is equivalent to setting both `marginTop` and `marginBottom`
marginTop	<number>	Corresponds to `CSS` margin-top property
marginRight	<number>	Corresponds to `CSS` margin-right property
marginBottom	<number>	Corresponds to `CSS` margin-bottom property
marginLeft	<number>	Corresponds to `CSS` margin-left property

Padding（7）

Propery Name	Values	Description
padding	<number>	Corresponds to `CSS` padding property, The difference is that it can only define one parameter, if you want to define the internal white of `top, right, bottom and left` 4 directions respectively, you can use the following one-way internal white property
paddingHorizontal	<number>	There is no corresponding `CSS` property. This has the effect of setting both `paddingRight` and `paddingLeft` at the same time
paddingVertical	<number>	No corresponding `CSS` property. The effect is equivalent to setting both `paddingTop` and `paddingBottom`.
paddingTop	<number>	Corresponds to `CSS` padding-top property
paddingRight	<number>	Corresponds to `CSS` padding-right property
paddingBottom	<number>	Corresponds to `CSS` padding-bottom property
paddingLeft	<number>	Corresponds to `CSS` padding-left property

Border （20）

Propery Name	Values	Description
borderStyle	`solid`, `dotted`, `dashed`	Corresponds to `CSS` `border-style` property，but with fewer `none, hidden, double, groove, ridge, inset, outset` fetch values and no direction splitting property
borderWidth	<number>	Corresponds to `CSS` `border-width` property
borderTopWidth	<number>	Corresponds to `CSS` `border-top-width` property
borderRightWidth	<number>	Corresponds to `CSS` `border-right-width` property
borderBottomWidth	<number>	Corresponds to `CSS` `border-bottom-width` property
borderLeftWidth	<number>	Corresponds to `CSS` `border-left-width` property
borderColor	<color>	Corresponds to `CSS` `border-color` property
borderTopColor	<color>	Corresponds to `CSS` `border-top-color` property
borderRightColor	<color>	Corresponds to `CSS` `border-right-color` property
borderBottomColor	<color>	Corresponds to `CSS` `border-bottom-color` property
borderLeftColor	<color>	Corresponds to `CSS` `border-left-color` property
borderRadius	<number>	Corresponds to `CSS` `border-radius` property
borderTopLeftRadius	<number>	Corresponds to `CSS` `border-top-left-radius` property
borderTopRightRadius	<number>	Corresponds to `CSS` `border-top-right-radius` property
borderBottomLeftRadius	<number>	Corresponds to `CSS` `border-bottom-left-radius`property
borderBottomRightRadius	<number>	Corresponds to `CSS` `border-bottom-right-radius` property
shadowColor	<color>	Corresponds to `CSS` box-shadow the color definition in the property
shadowOffset	{ width: <number>, height: <number> }	Corresponds to `CSS` box-shadow shadow offset definition in the properties
shadowRadius	<number>	In `CSS`, the size of the rounded corners of the shadow depends on the element's rounded corner definition and does not need to be defined additionally
shadowOpacity	<number>	Corresponds to `CSS` box-shadow shadow transparency definition in the properties

Background (1)

Propery Name	Values	Description
backgroundColor	<color>	Corresponds to `CSS` `background-color` propery

Transform （3）

Propery Name	Values	Description
transform	`[{perspective: number}, {rotate: string}, {rotateX: string}, {rotateY: string}, {rotateZ: string}, {scale: number}, {scaleX: number}, {scaleY: number}, {translateX: number}, {translateY: number}, {skewX: string}, {skewY: string}]`	Corresponds to `CSS` `transform` property
transformMatrix	`TransformMatrixPropType`	Similar to the `matrix()` and `matrix3d()` functions of the `transform` property in `CSS`
backfaceVisibility	`visible`, `hidden`	Corresponds to `CSS` `backface-visibility` propery

Flexbox （9）

We use Flexbox rules in React Native to specify the layout of a component's child elements, and Flexbox provides a consistent layout structure across screen sizes.

In general, most layout needs are met using the flexDirection, alignItems, and justifyContent style properties.

Flex number

In React Native, flex behaves a bit differently than CSS. flex can only be an integer value in RN, please refer to the yoga engine documentation for details

Conditions	Performance
When flex is set to a positive integer, e.g. `flex: 1`	The component is flexible and the size is proportional to the value of flex
`flex:0`	The component is not flexible, and the size and width and height are consistent
`flex: -1`	If there is enough space, the size of the component is the same as width and height; however, when there is not enough space, the component is compressed to minWidth and minHeight

Flex Direction

Specifying flexDirection in the component's style determines the main axis of the layout. Should the child elements be aligned along the horizontal axis (row) or along the vertical axis (column)? The default value is column direction, which is different from CSS and should be noted.

Justify Content

Specifying justifyContent in the component's style determines how its child elements are arranged along the main axis. Should the child elements be distributed close to the beginning or the end of the main axis? Or should they be evenly distributed? The options are: flex-start, center, flex-end, space-around and space-between.

Align Items

Specifying alignItems in the component's style determines how its child elements are arranged along the secondary axis (the axis perpendicular to the major axis, e.g. if the major axis is row, the secondary axis is column). Should the child elements be distributed near the beginning or the end of the secondary axis? Or should they be evenly distributed? The options are: flex-start, center, flex-end and stretch.

Propery Name	Values	Description
flex	<number>	Corresponds to `CSS` `flex` property，But only as integer values
flexGrow	<number>	Corresponds to `CSS` `flex-grow` property
flexShrink	<number>	Corresponds to `CSS` `flex-shrink` property
flexBasis	<number>	Corresponds to `CSS` `flex-basis` property
flexDirection	`row`, `row-reverse`, `column`, `column-reverse`	Corresponds to `CSS` `flex-direction` property
flexWrap	`wrap`, `nowrap`	Corresponds to `CSS` `flex-wrap` property, but the `wrap-reverse` fetch is missing
justifyContent	`flex-start`, `flex-end`, `center`, `space-between`, `space-around`	Corresponds to `CSS` `justify-content` property，but the `stretch` fetch is missing
alignItems	`flex-start`, `flex-end`, `center`, `stretch`	Corresponds to `CSS` `align-items` property，but the `baseline` fetch is missing
alignSelf	`auto`, `flex-start`, `flex-end`, `center`, `stretch`	Corresponds to `CSS` `align-self` property，but the `baseline` fetch is missing

Other

Propery Name	Values	Description
opacity	<number>	Corresponds to `CSS` `opacity` property
overflow	`visible`, `hidden`, `scroll`	Corresponds to `CSS` `overflow` property, but the `auto` fetch is missing
elevation ^Android	<number>	No corresponding property in `CSS`, only available on `Android 5.0+`
resizeMode	`cover`, `contain`, `stretch`	There is no equivalent property in `CSS`, you can refer to the `background-size` property
overlayColor ^Android	string	There is no equivalent property in `CSS` to fill the corners with a color when the image has rounded corners
tintColor ^iOS	<color>	No corresponding property in `CSS`, special color on `iOS` images, change color of opaque pixels

Color

React Native supports most of the color types in CSS.

#f00 (#rgb)
#f00c (#rgba)：No corresponding value in CSS
#ff0000 (#rrggbb)
#ff0000cc (#rrggbbaa)：No corresponding value in CSS
rgb(255, 0, 0)
rgba(255, 0, 0, 0.9)
hsl(360, 100%, 100%)
hsla(360, 100%, 100%, 0.9)
transparent
0xff00ff00 (0xrrggbbaa)：No corresponding value in CSS
Color Name：Support to Basic color keywords and Expanded color keywords，But not support 28 system colors；

Specificity and inheritance

The introduction style of a component has a higher priority than the global style.

Selector

Basic selector only supports class selector
Not support the combination selector writing method
Not support for pseudo-classes and pseudo-elements

Shorthand properties

Only accepts values supported by React Native. For example, background accepts only one color, backgroundColor, because React Native's Background only supports the backgroundColor property. properties supported by React Native can be found in the React Native stylesheet above.

Unit

Taro use PostCSS unit conversion plugin postcss-pxtransform will convert px to React Native's pt, see the documentation for details on how to configure this.

Taro 3 requires version 3.1 or higher

一、Layout​

flex​

position​

二、Styles​

Selectors​

Conditional compilation of styles​

Conditional compilation of style files​

Conditional compilation of style code​

Global introduction of styles​

三、Navigation

Global Configuration​

Page Config​

Frequently Asked Questions​

1. Can box-shadow be implemented?​

2、border{Top,Right,Bottom,Left} not supported ?​

3. React Native doesn't support background-image, is there any solution?s​

Support for each property​

Text （18）​

Dimension (6)​

Positioning （6）​

Margin（7）​

Padding（7）​

Border （20）​

Background (1)​

Transform （3）​

Flexbox （9）​

Flex number​

Flex Direction​

Justify Content​

Align Items​

Other​

Color​

Specificity and inheritance​

Selector​

Shorthand properties​

Unit​

一、Layout

flex

position

二、Styles

Selectors

Conditional compilation of styles

Conditional compilation of style files

Conditional compilation of style code

Global introduction of styles

Global Configuration

Page Config

Frequently Asked Questions

1. Can box-shadow be implemented?

2、border{Top,Right,Bottom,Left} not supported ?

3. React Native doesn't support background-image, is there any solution?s

Support for each property

Text （18）

Dimension (6)

Positioning （6）

Margin（7）

Padding（7）

Border （20）

Background (1)

Transform （3）

Flexbox （9）

Flex number

Flex Direction

Justify Content

Align Items

Other

Color

Specificity and inheritance

Selector

Shorthand properties

Unit