How to pass data to SectionList?

what's wrong is the first you try to pass a function to section props, not a value. to get value return from a function, you need to execute that function. Example :

sections={(()=>[
         {data: [{title:123},{title:"aaa"}], key: "aaa"},
          {data: [{title:333},{title:"bbbb"}], key: "bbb"},
          {data: [{title:123},{title:"aaa"}], key: "ccc"},
          ]) () <<< execute function 
          }
         />

Sections props require an array not a function. To use a function in sections props, this function must return an array. The array should contain a string key, and a data object. You can use many parameter in this object, for must information you can consult this page

example:

export default class Example extends React.Component {

  selectionList = () => {
    return([
      {data: [{title:123},{title:"aaa"}], key: "aaa"},
      {data: [{title:333},{title:"bbbb"}], key: "bbb"},
      {data: [{title:123},{title:"aaa"}], key: "ccc"},
    ])
  }

  render () {
    return (
      <View>
        <SectionList
          renderItem={({item}) => <View><Text> title={item.title}</Text></View>}
          renderSectionHeader={({section}) => <View><Text> title={section.key}</Text></View>}
          sections={this.selectionList()}
        />
      </View>
    )
  }
}