uniapp微信小程序下载base64图片流或https图片

 常规https的图片下载是这样的

const urlPath = 'https://test/logo.png'
uni.downloadFile({url: urlPath,success(res){// 这时会产生一个临时路径，在应用本次启动期间可以正常使用。if (res.statusCode == 200) {// 需要将图片保存到相册uni.saveImageToPhotosAlbum({filePath: res.tempFilePath, // 图片文件路径，可以是临时文件路径也可以是永久文件路径，不支持网络图片路径success(res){uni.showToast({title: '保存成功',icon: 'none'})// 如果保存成功需要打开查看，请使用以下方法，同时也支持打开文件uni.openDocument({filePath: res.savedFilePath,success(res){},fail(err){uni.showToast({title: '手机不支持该文件类型，请安装wps或office应用',icon: 'none'})}})},fail(err){uni.showToast({title: '图片保存失败',icon: 'none'})}})} else {uni.showToast({title: '下载失败,请稍后再试',icon: 'none'})}},fail(err) {uni.showToast({title: '下载失败,请稍后再试',icon: 'none'})}
})

下面来说一下后端返回base64的文件流，是如何下载的

必须把返回的流去掉这一部分：data:image/png;base64，否则下载不了

如我自己的流：

data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAJYAAACgCAIAAABhQAIFAAACaklEQVR42u3aUXLCMAwEUO5/6fYKMNLKcvL2k4E08UsHsfHnTy7PxxIgFISCEKEgFISCEKEgFISCEKEgFISCEKEgFISCEKG8h/ATyK9/q3KeXZ+dXAeECBEiRLiXsPQ9/MXSVD5bec+GdUCIECFChPcR/vp1XRlnKsfvGjcm1wEhQoQIEb6LsOv1xHsQIkSIECHCk+NM18/nyVsQIUKECBG+i3Cy5u76qb7t9kKIECFChPcRTi7f5tftYEOIECHCdxFOJnHZlUfNG5cIIUKECBHOEybGljRV5ZiTIxhChAgRIryb8FQFnN4ulRidECJEiBDhcwi7Rp7KElSOmR5DBioChAgRIkS4tOY+tTWoi3Pyce7SR74IESJEiLCx5k4fp6vmXlhhI0SIECHCpYSJyjtx2ZO3xanHAAgRIkSIcNfzwlMVdtfWpq5KYXJkQ4gQIUKEZwgT40NiS1J6+1P6sTNChAgRItxLOLkEiUfHm6t5hAgRIkR4H2Hip3e6Ou+qudNjF0KECBEivIMwTV45/mRln6g7ECJEiBDh3YTpCji9rF1J/EsgRIgQIcK7CRtPvb2G7qrjh6twhAgRIkR4gDCdyhKn+RO3OEKECBEivI8w/ZU+uSWpcg6JLcIIESJEiPA+wsTYkq4LTtXWIVqECBEiRLiIcLJW3jCSdI1pCBEiRIgQYXUk6arLE9XBxFMBhAgRIkT4bMKucWOSuVJNIESIECHCuwnTt0LiHCavMXQtCBEiRIjwMOEtdfDkcexgQ4gQIcLnE8qqIEQoCAUhQkEoCAUhQkEoCAUhQkEoCAUhQkEoCAUhQrk0/1j3Eulg4ZAoAAAAAElFTkSuQmCC

downImg(){var byte=this.codeImg.replace("data:image/png;base64,","");const fs = uni.getFileSystemManager(); //全局唯一的文件管理器var number = Math.random();fs.writeFile({filePath: wx.env.USER_DATA_PATH + '/code' + number + '.png',data: byte,encoding: "base64",success(res) {uni.saveImageToPhotosAlbum({ //保存为png格式到相册filePath: wx.env.USER_DATA_PATH + '/code' + number + '.png',success: function (res) {uni.showToast({ title: "下载成功", icon: "success" });},fail: function (err) {console.log(err)}})}})},