uniapp开发微信小程序，使用uni.downloadFile下载图片时失败问题

做一个长按保存图片功能，在微信开发者工具中能够成功，自己在真机上试时，下载图片失败，贴上代码片段，请问原因是什么？

uni.downloadFile({  
                    url: data.src,  
                    success: (resFile) => {  
                        console.log(resFile, "resFile");  
                        if (resFile.statusCode === 200) {  
                            uni.getSetting({  
                                success: (res) => {  
                                    if (!res.authSetting["scope.writePhotosAlbum"]) {  
                                        uni.authorize({  
                                            scope: "scope.writePhotosAlbum",  
                                            success: () => {  
                                                uni.saveImageToPhotosAlbum({  
                                                    filePath: resFile  
                                                        .tempFilePath,  
                                                    success: (res) => {  
                                                        return uni  
                                                            .showToast({  
                                                                title: "保存成功！",  
                                                            });  
                                                    },  
                                                    fail: (res) => {  
                                                        return uni  
                                                            .showToast({  
                                                                title: '保存文件失败',  
                                                            });  
                                                    },  
                                                    complete: (res) => {},  
                                                });  
                                            },  
                                            fail: () => {  
                                                uni.showModal({  
                                                    title: "您已拒绝获取相册权限",  
                                                    content: "是否进入权限管理，调整授权？",  
                                                    success: (res) => {  
                                                        if (res.confirm) {  
                                                            uni.openSetting({  
                                                                success: (  
                                                                    res  
                                                                ) => {  
                                                                    console  
                                                                        .log(  
                                                                            res  
                                                                            .authSetting  
                                                                        );  
                                                                },  
                                                            });  
                                                        } else if (res  
                                                            .cancel) {  
                                                            return uni  
                                                                .showToast({  
                                                                    title: "已取消！",  
                                                                });  
                                                        }  
                                                    },  
                                                });  
                                            },  
                                        });  
                                    } else {  
                                        uni.saveImageToPhotosAlbum({  
                                            filePath: resFile.tempFilePath,  
                                            success: (res) => {  
                                                return uni.showToast({  
                                                    title: "保存成功！",  
                                                });  
                                            },  
                                            fail: (res) => {  
                                                return uni.showToast({  
                                                    title: res.errMsg,  
                                                });  
                                            },  
                                            complete: (res) => {},  
                                        });  
                                    }  
                                },  
                                fail: (res) => {},  
                            });  
                        } else {  
                            return uni.showToast({  
                                title: resFile.errMsg,  
                            });  
                        }  
                    },  
                    fail: (res) => {  
                        return uni.showToast({  
                            title: '下载文件失败',  
                        });  
                    },  
                });