如何理解和重写onBackPress生命周期

import { router } from '@kit.ArkUI' 
 
@Entry 
@Component 
struct IndexComponent { 
  onBackPress() { 
    return true 
    router.pushUrl({ 
      url: 'pages/Index', 
      params: '' 
    }, (err) => { 
      if (err) { 
        console.error(`pushUrl failed, code is ${err.code}, message is ${err.message}`); 
        return; 
      } 
      console.info('pushUrl success'); 
    }) 
  } 
 
  build() { 
    Column() { 
      Text('Hello World') 
        .fontColor(Color.Black) 
        .fontSize(30) 
        .margin(30) 
    }.width('100%') 
  } 
}