Question

我有一个在后台持续运行的应用程序，需要将数据写入文件。偶尔我会发现写入该文件的部分记录，所以我添加了一些额外的代码来尝试确保即使应用程序是背景的，它仍然有可能完成任何写入。

到目前为止，这是代码，它似乎工作但我仍然不确定我使用的API是否是这项工作的最佳选择。

例如，有没有更好的方法打开文件并保持打开状态，以便每次都不必寻找文件的末尾？

将任务标记为后台任务的方法是否正确，以确保iOS允许任务完成 - 它大约每秒执行一次。

 /// We wrap this in a background task to ensure that task will complete even if the app is switched to the background
 /// by the OS
 func asyncWriteFullData(dataString: String, completion: (() -> Void)?) {

    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), {

        let taskID = self.beginBackgroundUpdateTask()

        self.writeFullData(dataString)

        self.endBackgroundUpdateTask(taskID)

        if (completion != nil) {
            completion!()
        }

    })
}
func beginBackgroundUpdateTask() -> UIBackgroundTaskIdentifier {
    return UIApplication.sharedApplication().beginBackgroundTaskWithExpirationHandler({})
}

func endBackgroundUpdateTask(taskID: UIBackgroundTaskIdentifier) {
    UIApplication.sharedApplication().endBackgroundTask(taskID)
}
/// Write the record out to file.  If the file does not exist then
/// create it.
private func writeFullData(dataString: String) {


    let filemgr = NSFileManager.defaultManager()

    if let filePath = self.fullDataFilePath {

    if filemgr.fileExistsAtPath(filePath) {

        if filemgr.isWritableFileAtPath(filePath) {

            let file: NSFileHandle? = NSFileHandle(forUpdatingAtPath: filePath)

            if file == nil {
                // This is a major problem so best notify the User 
                // How are we going to handle this type of error ?
                DebugLog("File open failed for \(self.fullDataFilename)")
                AlertManager.sendActionNotification("We have a problem scanning data, please contact support.");

            } else {
                let data = (dataString as
                    NSString).dataUsingEncoding(NSUTF8StringEncoding)
                file?.seekToEndOfFile()
                file?.writeData(data!)
                file?.closeFile()
            }

        } else {
            //print("File is read-only")
        }

    } else {
        //print("File not found")

        if createFullDataFile() {
            // Now write the data we were asked to write
            writeFullData(dataString)
        } else {
            DebugLog("Error unable to write Full Data record")
        }

    }
    }
}

Answer 1

我建议你使用NSOutputStream。此外，GCD IO还可以处理您的工作。

Techniques for Reading and Writing Files Without File Coordinators

如何在后台将数据写入iOS上的文件

1 个答案: