px2vp 在context.getLastWindow回调之前无效

import { display } from '@kit.ArkUI';  
@Entry  
@Component  
struct Example {  
  aboutToAppear() {  
    let displayClass: display.Display | null = null;  
    try {  
      displayClass = display.getDefaultDisplaySync();  
      let test1 = px2vp(20)  
      let test2 = 20/displayClass.densityPixels //实际效果等同于px2vp(20)  
      console.info('test1='+test1+' test2='+test2)  
    } catch (exception) {  
      console.error('Failed to obtain the default display object. Code: ' + JSON.stringify(exception));  
    }  
  }  
  build() {  
    Column() {  
    }.width('100%')  
  }  
}