小程序下载图片saveImageToPhotosAlbum “saveImageToPhotosAlbum:fail file not exists“

	// 下载预览文件
	onSaveClick: function (e) {
		let _this = this;
		let path = e.currentTarget.dataset.path;
		wx.showLoading({
			title: '下载中...',
		})
		var filename = new Date().getTime() + ".jpg";
		var savePath = wx.env.USER_DATA_PATH + "/" + filename
		wx.downloadFile({
			header: 'content-type: image/jpg',
			url: path,
			filePath: savePath,
			success: function (res) {
				wx.hideLoading({
					success: (res) => {},
				})
				var filePath = res.filePath
				_this.setData({
					filePath: filePath
				})
				wx.getSetting({
					success: (res) => {
						console.log('getSetting', res);
						var writePhotosAlbum = res.authSetting['scope.writePhotosAlbum'];
						if (writePhotosAlbum == true) {
							_this.saveImg()
						} else if (writePhotosAlbum == false) {
							wx.showModal({
								title: '是否授权保存到相册',
								content: '需要获取您的保存图片权限，请确认授权，否则图片将无法保存到相册',
								success: function (tip) {
									if (tip.confirm) {
										wx.openSetting({
											success: function (data) {
												if (data.authSetting["scope.writePhotosAlbum"] === true) {
													_this.saveImg()
												} else {
													wx.showToast({
														title: '授权失败',
													})
												}
											}
										})
									}
								}
							})
						} else {
							_this.saveImg()
						}
					},
					fail: function (res) {},
					complete: () => {}
				})
			}
		})

	},

	saveImg: function () {
		var filePath = this.data.filePath
		wx.showLoading({
			title: '保存中...',
		})
		wx.saveImageToPhotosAlbum({
			filePath: filePath,
			success: function (res) {
				wx.hideLoading({
					success: (res) => {},
				})
				wx.showToast({
					title: '保存成功',
					icon: 'success',
					duration: 1500,
				})
			},
			fail: function (res) {
				wx.showToast({
					title: "保存失败：" + res.errMsg,
					icon: 'none',
					duration: 1500,
				})
			},
			complete: function (res) {},
		})
	},