React NativeText
A React component for displaying text which supports nesting,
styling, and touch handling. In the following example, the nested title and
body text will inherit the fontFamily from styles.baseText, but the title
provides its own additional styles. The title and body will stack on top of
each other on account of the literal newlines:
Edit on GitHubProps #
numberOfLines number #
Used to truncate the text with an elipsis after computing the text layout, including line wrapping, such that the total number of lines does not exceed this number.
onLayout function #
Invoked on mount and layout changes with
{nativeEvent: { layout: {x, y, width, height}}}.
onPress function #
This function is called on press. Text intrinsically supports press
handling with a default highlight state (which can be disabled with
suppressHighlighting).
style style #
color string
containerBackgroundColor string
fontFamily string
fontSize number
fontStyle enum('normal', 'italic')
fontWeight enum("normal", 'bold', '100', '200', '300', '400', '500', '600', '700', '800', '900')
letterSpacing number
lineHeight number
textAlign enum("auto", 'left', 'right', 'center', 'justify')
writingDirection enum("auto", 'ltr', 'rtl')
suppressHighlighting bool #
When true, no visual change is made when text is pressed down. By default, a gray oval highlights the text on press down.
testID string #
Used to locate this view in end-to-end tests.
Edit on GitHubDescription #
Nested Text #
In iOS, the way to display formatted text is by using NSAttributedString: you give the text that you want to display and annotate ranges with some specific formatting. In practice, this is very tedious. For React Native, we decided to use web paradigm for this where you can nest text to achieve the same effect.
Behind the scenes, this is going to be converted to a flat NSAttributedString that contains the following information
Containers #
The <Text> element is special relative to layout: everything inside is no longer using the flexbox layout but using text layout. This means that elements inside of a <Text> are no longer rectangles, but wrap when they see the end of the line.
Limited Style Inheritance #
On the web, the usual way to set a font family and size for the entire document is to write:
When the browser is trying to render a text node, it's going to go all the way up to the root element of the tree and find an element with a font-size attribute. An unexpected property of this system is that any node can have font-size attribute, including a <div>. This was designed for convenience, even though not really semantically correct.
In React Native, we are more strict about it: you must wrap all the text nodes inside of a <Text> component; you cannot have a text node directly under a <View>.
You also lose the ability to set up a default font for an entire subtree. The recommended way to use consistent fonts and sizes across your application is to create a component MyAppText that includes them and use this component across your app. You can also use this component to make more specific components like MyAppHeaderText for other kinds of text.
React Native still has the concept of style inheritance, but limited to text subtrees. In this case, the second part will be both bold and red.
We believe that this more constrained way to style text will yield better apps:
(Developer) React components are designed with strong isolation in mind: You should be able to drop a component anywhere in your application, trusting that as long as the props are the same, it will look and behave the same way. Text properties that could inherit from outside of the props would break this isolation.
(Implementor) The implementation of React Native is also simplified. We do not need to have a
fontFamilyfield on every single element, and we do not need to potentially traverse the tree up to the root every time we display a text node. The style inheritance is only encoded inside of the native Text component and doesn't leak to other components or the system itself.