1. 获取到的文件流转成base64, 

2. base64转成图片，这里使用了插件https://ext.dcloud.net.cn/plugin?id=123

uni.request({
					url: `${url.baseUrl}/api/services/Muster/SpecializedMeetingManageService/GetQrCode`, //请求文件流地址
					method: 'GET',
					data: param, //请求参数
					header: {
						'access_token': uni.getStorageSync('access_token')
					},
					responseType: "arraybuffer",
					success: res => {
						let datas = res.data;
						this.qrUrl = 'data:image/png;base64,'+ uni.arrayBufferToBase64(res.data)
						let images = [];
						base64ToPath(this.qrUrl).then(path=>{
							images[0] = path;
							uni.previewImage({
								current: 0,
								urls: images
							});
						})
					},
					fail: () => {
						uni.showToast({
							title: '获取数据失败，请稍后再试！',
							duration: 2000,
							icon: 'none',
						});
					},
					complete: () => {},
				});