I am styling an Image component with flexbox to be in the center of the screen which works pretty well. Now I want a second Image component to be displayed directly on the top of the first one. The second image is using absolute positioning. Currently I'm just guessing pixels so that it fits, but of course this is not accurate and way too much maintainability effort.
I am pretty much looking for the React Native equivalent of jQuery's .offset(). Is there such a thing and if there isn't what's the best way to achieve this?
React Native provides a .measure(...) method which takes a callback and calls it with the offsets and width/height of a component:
myComponent.measure( (fx, fy, width, height, px, py) => {
console.log('Component width is: ' + width)
console.log('Component height is: ' + height)
console.log('X offset to frame: ' + fx)
console.log('Y offset to frame: ' + fy)
console.log('X offset to page: ' + px)
console.log('Y offset to page: ' + py)
})
The following calculates the layout of a custom component after it is rendered:
class MyComponent extends React.Component {
render() {
return <View ref={view => { this.myComponent = view; }} />
}
componentDidMount() {
// Print component dimensions to console
this.myComponent.measure( (fx, fy, width, height, px, py) => {
console.log('Component width is: ' + width)
console.log('Component height is: ' + height)
console.log('X offset to frame: ' + fx)
console.log('Y offset to frame: ' + fy)
console.log('X offset to page: ' + px)
console.log('Y offset to page: ' + py)
})
}
}
Note that sometimes the component does not finish rendering before componentDidMount() is called. If you are getting zeros as a result from measure(...), then wrapping it in a setTimeout should solve the problem, i.e.:
setTimeout( myComponent.measure(...), 0 )
You can use onLayout to get the width, height, and relative-to-parent position of a component at the earliest moment that they're available:
<View
onLayout={event => {
const layout = event.nativeEvent.layout;
console.log('height:', layout.height);
console.log('width:', layout.width);
console.log('x:', layout.x);
console.log('y:', layout.y);
}}
>
Compared to using .measure() as shown in the accepted answer, this has the advantage that you'll never have to fiddle around deferring your .measure() calls with setTimeout to make sure that the measurements are available, but the disadvantage that it doesn't give you offsets relative to the entire page, only ones relative to the element's parent.
I had a similar problem and solved it by combining the answers above
class FeedPost extends React.Component {
constructor(props) {
...
this.handleLayoutChange = this.handleLayoutChange.bind(this);
}
handleLayoutChange() {
this.feedPost.measure( (fx, fy, width, height, px, py) => {
console.log('Component width is: ' + width)
console.log('Component height is: ' + height)
console.log('X offset to page: ' + px)
console.log('Y offset to page: ' + py)
})
}
render {
return(
<View onLayout={(event) => {this.handleLayoutChange(event) }}
ref={view => { this.feedPost = view; }} >
...
Now I can see the position of my feedPost element in the logs:
08-24 11:15:36.838 3727 27838 I ReactNativeJS: Component width is: 156
08-24 11:15:36.838 3727 27838 I ReactNativeJS: Component height is: 206
08-24 11:15:36.838 3727 27838 I ReactNativeJS: X offset to page: 188
08-24 11:15:36.838 3727 27838 I ReactNativeJS: Y offset to page: 870