HarmonyOS renderNode的frame设置问题

makeNode(uiContext: UIContext): FrameNode | null { 
  this.rootNode = new FrameNode(uiContext); 
  const renderNode = this.rootNode.getRenderNode(); 
  if (renderNode !== null) { 
    let newNode = new MyRenderNode(); 
    const width: number = renderNode.frame.width // 为0 
    const height: number = renderNode.frame.height // 为0，怎么能取到呢，rootNode和uiContext好像都拿不到frame信息 
    newNode.frame = { x: 0, y: 0, width: width, height: height } 
    newNode.onDrawCB = this.onDrawCB 
    renderNode.appendChild(newNode); 
  } 
  return this.rootNode; 
}