HarmonyOS 绝对定位如何让组件在屏幕正中间

import window from '@ohos.window';  
import { BreakpointSystem, Num } from './Util';  
import display from '@ohos.display';  
  
@Entry  
@Component  
struct Index {  
  @State message: string = 'Hello World';  
  @State buttonWidth: number = 100;  
  @State buttonHeight: number = 50;  
  @State x: number = 0;  
  @State y: number = 0;  
  
  aboutToAppear() {  
    display.getAllDisplays((err, data) => {  
      let screenWidth: number = data[0].width  
      let screenHeight: number = data[0].height  
      // 将长度的单位由px换算为vp  
      let windowWidthVp = screenWidth / display.getDefaultDisplaySync().densityPixels  
      let windowHeightVp = screenHeight / display.getDefaultDisplaySync().densityPixels  
      this.x = (windowWidthVp-this.buttonWidth)/2  
      this.y = (windowHeightVp-this.buttonHeight)/2 - this.buttonHeight/2  
    })  
  }  
  build() {  
  
    Column() {  
      Button('点击')  
        .fontColor('#ffef1515')  
        .width(this.buttonWidth+'vp')  
        .height(this.buttonHeight+'vp')  
        .position({ x: this.x, y:  this.y})  
        .backgroundColor('#fff3d579')  
    }.width('100%')  
    .height('100%')  
  }  
}

@Entry  
@Component  
struct Index {  
  @State message: string = 'Hello World';  
  @State buttonWidth: number = 100;  
  @State buttonHeight: number = 50;  
  build() {  
    Column() {  
      Button('点击')  
        .fontColor('#ffef1515')  
        .width(this.buttonWidth+'vp')  
        .height(this.buttonHeight+'vp')  
        .backgroundColor('#fff3d579')  
    }  
    .justifyContent(FlexAlign.Center)  
    .width('100%')  
    .height('100%')  
  }  
  
}