读取和写入文本文件中的数据 [英] Read and write data from text file

问题描述

我需要从文本文件中读取/写入数据，但是我一直无法弄清楚。

我发现这个示例代码Swift的iBook，但我仍然不知道如何写或读数据。

  import Cocoa 
 
 class DataImporter 
 {
 / * 
 DataImporter是一个从外部文件导入数据的类。 
假设这个班级需要花费很少的时间进行初始化。 
 * / 
 var fileName =data.txt
 // DataImporter类将在这里提供数据导入功能
 
 $ b $ class DataManager 
 
 @lazy var importer = DataImporter（）
 var data = String []（）
 // DataManager类在这里提供数据管理功能
 
 
让manager = DataManager（）
 manager.data + =某些数据
 manager.data + =更多数据
 //导入器的DataImporter实例属性尚未创建
 
 println（manager.importer.fileName）
 //导入器属性的DataImporter实例现在已创建
 //打印数据。 txt
 
 
 
 var str =Swift语言中的Hello World。
  

$ b $对于读写，你应该使用一个可写的位置，例如文档目录下面的代码展示了如何读写一个简单的字符串。能够

Swift 1.x

如果让dirs：[String] = NSSearchPathForDirectoriesInDomains（NSSearchPathDirectory.DocumentDirectory，NSSearchPathDomainMask.AllDomainsMask，true）作为参数，则file =file.txt
 
 [String] {
 let dir = dirs [0] // documents directory 
 let path = dir.stringByAppendingPathComponent（file）; 
 let text =some text
 
 //写入
 text.writeToFile（path，atomically：false，encoding：NSUTF8StringEncoding，error：nil）; 
 $ b //阅读
让text2 = String（contentsOfFile：path，encoding：NSUTF8StringEncoding，error：nil）
} 
  pre> 
 
 
  Swift 2.2   
 
 
  let file =file.txt//这是文件。我们将写入和读取
 
让text =一些文本//只是一个文本
 
如果让dir = NSSearchPathForDirectoriesInDomains（NSSearchPathDirectory.DocumentDirectory，NSSearchPathDomainMask.AllDomainsMask， true）.first {
 let path = NSURL（fileURLWithPath：dir）.URLByAppendingPathComponent（file）
 
 //写入
 do {
 try text.writeToURL（path ，原子：false，编码：NSUTF8StringEncoding）
} 
 catch {/ *错误处理在这里* /} 
 
 //读$ b $ do {
 let text2 = try NSString（contentsOfURL：path，encoding：NSUTF8StringEncoding）
} 
 catch {/ *错误处理在这里* /} 
} 
  pre> 
 
 
  Swift 3.x和Swift 4.0   
 
 
  let file =file.txt//这是文件。我们将写入和读取它
 
让text =一些文本//只是一个文本
 
如果让dir = FileManager.default.urls（for：.documentDirectory ，在：.userDomainMask）.first {
 
 let fileURL = dir.appendingPathComponent（file）
 
 //写
 do {
尝试文字。写（到：fileURL，原子：false，编码：.utf8）
} 
 catch {/ *错误处理在这里* /} 
 
 //读
 {
让text2 = try String（contentsOf：fileURL，encoding：.utf8）
} 
 catch {/ *错误处理在这里* /} 
} 
  
 
I need to read and write data to/from a text file, but I haven't been able to figure out how.


I found this sample code in the Swift's iBook, but I still don't know how to write or read data.
import Cocoa

class DataImporter
{
    /*
    DataImporter is a class to import data from an external file.
    The class is assumed to take a non-trivial amount of time to initialize.
    */
    var fileName = "data.txt"
    // the DataImporter class would provide data importing functionality here
}

class DataManager
{
    @lazy var importer = DataImporter()
    var data = String[]()
    // the DataManager class would provide data management functionality here
}

let manager = DataManager()
manager.data += "Some data"
manager.data += "Some more data"
// the DataImporter instance for the importer property has not yet been created"

println(manager.importer.fileName)
// the DataImporter instance for the importer property has now been created
// prints "data.txt"



var str = "Hello World in Swift Language."

解决方案
For reading and writing you should use a location that is writeable, for example documents directory. The following code shows how to read and write a simple string. You can test it on a playground.

Swift 1.x
let file = "file.txt"

if let dirs : [String] = NSSearchPathForDirectoriesInDomains(NSSearchPathDirectory.DocumentDirectory, NSSearchPathDomainMask.AllDomainsMask, true) as? [String] {
    let dir = dirs[0] //documents directory
    let path = dir.stringByAppendingPathComponent(file);
    let text = "some text"

    //writing
    text.writeToFile(path, atomically: false, encoding: NSUTF8StringEncoding, error: nil);

    //reading
    let text2 = String(contentsOfFile: path, encoding: NSUTF8StringEncoding, error: nil)
}
Swift 2.2
let file = "file.txt" //this is the file. we will write to and read from it

let text = "some text" //just a text

if let dir = NSSearchPathForDirectoriesInDomains(NSSearchPathDirectory.DocumentDirectory, NSSearchPathDomainMask.AllDomainsMask, true).first {
    let path = NSURL(fileURLWithPath: dir).URLByAppendingPathComponent(file)

    //writing
    do {
        try text.writeToURL(path, atomically: false, encoding: NSUTF8StringEncoding)
    }
    catch {/* error handling here */}

    //reading
    do {
        let text2 = try NSString(contentsOfURL: path, encoding: NSUTF8StringEncoding)
    }
    catch {/* error handling here */}
}
Swift 3.x and Swift 4.0
let file = "file.txt" //this is the file. we will write to and read from it

let text = "some text" //just a text

if let dir = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first {

    let fileURL = dir.appendingPathComponent(file)

    //writing
    do {
        try text.write(to: fileURL, atomically: false, encoding: .utf8)
    }
    catch {/* error handling here */}

    //reading
    do {
        let text2 = try String(contentsOf: fileURL, encoding: .utf8)
    }
    catch {/* error handling here */}
}


                        
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