HarmonyOS 图片转为base64字符串

let OutData: http.HttpResponse 
http.createHttp().request("https://xxx/xxx.png",//在线图片地址 
  (error: BusinessError, data: http.HttpResponse) => { 
    if (error) { 
      console.error(`http reqeust failed with. Code: ${error.code}, message: ${error.message}`); 
    } else { 
      OutData = data 
      let code: http.ResponseCode | number = OutData.responseCode 
      if (ResponseCode.ResponseCode.OK === code) { 
        let imageData: ArrayBuffer = OutData.result as ArrayBuffer; 
        let base64 = new util.Base64Helper(); // 实例化Base64Helper 
        let data = base64.encodeSync(new Uint8Array(imageData.slice(0, imageData.byteLength))) // 转换成Uint8Array 
        console.info(`data长度:${data.length}`) 
        console.info(`data:${data}`) 
        let textDecoder = util.TextDecoder.create('utf-8', { ignoreBOM : true }) 
        let retStr = textDecoder.decodeWithStream( data , {stream: false}); // 可以把Uint8Array转码成base64 
      } 
    } 
  } 
)