url地址必须为合法域名，且是https开头。否则测试环境和调试模式可以下载图片，体验版和正式版不可以

let url = $this.ewmSrc.replace('http:','https:')
					console.log(url)
					uni.downloadFile({
							url: url,
							success: (res) => {
								if (res.statusCode === 200) {
									uni.saveImageToPhotosAlbum({
										filePath: res.tempFilePath,
										success: function() {
											uni.showToast({
													title: '保存成功',
													duration: 1000
												})
				$this.$refs.dialogImg.close();
										},
										fail() {
										        wx.showModal({
										          title: '提示',
										          content: '需要您授权保存相册',
										          showCancel: false,
										          success() {
										            wx.openSetting({
										              success(settingdata) {
										                if (settingdata.authSetting['scope.writePhotosAlbum']) {//是否授权保存到相册
										                  wx.showModal({
										                    title: '提示',
										                    content: '获取权限成功,再次保存图片即可成功',
										                    showCancel: false,
										                  })
										                } else {
										                  wx.showModal({
										                    title: '提示',
										                    content: '获取权限失败，无法保存到相册',
										                    showCancel: false,
										                  })
										                }
										
										              },
										              complete(complet) {
										                console.log("complet", complet)
										              }
										            })
										          }
										        })
										      }
										})
								}
							},
							fail:() =>{
											uni.showToast({
													title: '下载失败',
													duration: 1000
												})
							}
						});