how get parent size in child view in react-native?

Question

I cannot understand how can I send parent view's sizes to child component of this. In renderPager() I want calculate some parameters that depend on parent view size. I know that we can do it through onLayout(). problem is that onLayout will be called only after building all of childs (I see it by the console log). how can I do it?

 onPageLayout = (event) => {
    const { width, height } = event.nativeEvent.layout;
    console.log("ON LAYOUT");
  }; 

render() {
    return (
      <View
        style={styles.root}
        onLayout={this.onPageLayout}
      >
        {this.renderPager()}
      </View>
    );
  }

renderPager = () => {
   // how can get root view's size here
    return (
      <IndicatorViewPager
        ref={(ref) => (this.viewPager = ref)}
        scrollEnabled={!this.state.isDragging}
        onPageScroll={this.onPageScroll}
        style={styles.pageRoot}
      >
        {this.renderPages()}
      </IndicatorViewPager>
    );
  };

thank you

Answer 1

You can maybe pass the data as props, and take the prop data from the store. You are right in that onLayout will only be triggered after everything is rendered, but that simply means that you have to pass the props with a null value on the first render. For instance:

onPageLayout = (event) => {
    const { width, height } = event.nativeEvent.layout;
    console.log("ON LAYOUT");
    this.setState({width, height})
  }; 

render() {
    return (
      <View
        style={styles.root}
        onLayout={this.onPageLayout}
      >
        {this.renderPager(this.state.width, this.state.height)}
      </View>
    );
  }

renderPager = (width, height) => {
   // Do something if width or height are null
   // how can get root view's size here
    return (
      <IndicatorViewPager
        ref={(ref) => (this.viewPager = ref)}
        scrollEnabled={!this.state.isDragging}
        onPageScroll={this.onPageScroll}
        style={styles.pageRoot}
      >
        {this.renderPages()}
      </IndicatorViewPager>
    );
  };

Also you could use the measure function of the parent, but I think that might be a bit cumbersome.