遇到一个崩溃，Task created in a session that has been invalidated

[gaoruiqing187]

bugly上显示一个崩溃，次数很多，我不知道哪里写错了 ，求指教 Task created in a session that has been invalidated

var sessionManager: SessionManager?
func createDownloadSession(identifier: String) {
var config = SessionConfiguration.init()
if #available(iOS 13, *) {
config.allowsExpensiveNetworkAccess = true
config.allowsConstrainedNetworkAccess = true
config.allowsCellularAccess = false
}
self.sessionManager = SessionManager(identifier, configuration: config)
}

func createDownloadTask(urlStr: String) -> DownloadTask? {
    guard let url = URL(string: urlStr) else { return nil }
    if (self.sessionManager == nil) {return nil}
    let task = self.sessionManager?.download(url)
    
    return task
}

[Danie1s]

sessionManager 生命周期问题，最好别销毁，具体的看一下文档