ios 将 UTF-8 编码的 NSData 转换为 NSString

Convert UTF-8 encoded NSData to NSString

提问by Ashwini Shahapurkar

I have UTF-8 encoded NSDatafrom windows server and I want to convert it to NSStringfor iPhone. Since data contains characters (like a degree symbol) which have different values on both platforms, how do I convert data to string?

我有NSData从 Windows 服务器编码的 UTF-8 ，我想将其转换NSString为 iPhone。由于数据包含在两个平台上具有不同值的字符（如度数符号），我如何将数据转换为字符串？

回答by kennytm

If the data is not null-terminated, you should use -initWithData:encoding:

如果数据不是以空值结尾的，你应该使用 -initWithData:encoding:

NSString* newStr = [[NSString alloc] initWithData:theData encoding:NSUTF8StringEncoding];

If the data is null-terminated, you should instead use -stringWithUTF8String:to avoid the extra \0at the end.

如果数据以空值结尾，则应改为使用-stringWithUTF8String:避免\0末尾的额外数据。

NSString* newStr = [NSString stringWithUTF8String:[theData bytes]];

(Note that if the input is not properly UTF-8-encoded, you will get nil.)

（请注意，如果输入的 UTF-8 编码不正确，您将获得nil.）

---

---

Swift variant:

Swift 变体：

let newStr = String(data: data, encoding: .utf8)
// note that `newStr` is a `String?`, not a `String`.

If the data is null-terminated, you could go though the safe way which is remove the that null character, or the unsafe way similar to the Objective-C version above.

如果数据以空字符结尾，您可以通过删除该空字符的安全方法，或类似于上述 Objective-C 版本的不安全方法。

// safe way, provided data is 
+(id)stringWithUTF8String:(const char *)bytes.
-terminated
let newStr1 = String(data: data.subdata(in: 0 ..< data.count - 1), encoding: .utf8)
// unsafe way, provided data is 
@interface NSData (EasyUTF8)

// Safely decode the bytes into a UTF8 string
- (NSString *)asUTF8String;

@end
-terminated
let newStr2 = data.withUnsafeBytes(String.init(utf8String:))

回答by Gouldsc

You could call this method

你可以调用这个方法

@implementation NSData (EasyUTF8)

- (NSString *)asUTF8String {
    return [[NSString alloc] initWithData:self encoding:NSUTF8StringEncoding];    
}

@end

回答by Claudiu

I humbly submit a category to make this less annoying:

我谦虚地提交一个类别，使这不那么烦人：

NSData *data = ...
[[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];

and

和

NSData *data = ...
[data asUTF8String];

(Note that if you're not using ARC you'll need an autoreleasethere.)

（请注意，如果您不使用 ARC，则需要在autorelease那里使用。）

Now instead of the appallingly verbose:

现在，而不是令人震惊的冗长：

extension Data {
    var string: String? {
        return String(data: self, encoding: .utf8)
    }
}

You can do:

你可以做：

extension StringProtocol {
    var data: Data {
        return Data(utf8)
    }
}

回答by Leo Dabus

The Swift version from String to Data and back to String:

从 String 到 Data 再到 String 的 Swift 版本：

Xcode 10.1 ? Swift 4.2.1

Xcode 10.1？斯威夫特 4.2.1

extension String {
    var base64Decoded: Data? {
        return Data(base64Encoded: self)
    }
}

---

---

let string = "Hello World"                                  // "Hello World"
let stringData = string.data                                // 11 bytes
let base64EncodedString = stringData.base64EncodedString()  // "SGVsbG8gV29ybGQ="
let stringFromData = stringData.string                      // "Hello World"

---

---

let base64String = "SGVsbG8gV29ybGQ="
if let data = base64String.base64Decoded {
    print(data)                                    //  11 bytes
    print(data.base64EncodedString())              // "SGVsbG8gV29ybGQ="
    print(data.string ?? "nil")                    // "Hello World"
}

---

---

Playground

操场

let stringWithAccent = "Olá Mundo"                          // "Olá Mundo"
print(stringWithAccent.count)                               // "9"
let stringWithAccentData = stringWithAccent.data            // "10 bytes" note: an extra byte for the acute accent
let stringWithAccentFromData = stringWithAccentData.string  // "Olá Mundo\n"

---

---

NSData *signature;
NSString *signatureString = [signature base64EncodedStringWithOptions:0];

---

---

let signatureString = signature.base64EncodedStringWithOptions(nil)

回答by mikeho

Sometimes, the methods in the other answers don't work. In my case, I'm generating a signature with my RSA private key and the result is NSData. I found that this seems to work:

有时，其他答案中的方法不起作用。就我而言，我使用 RSA 私钥生成签名，结果是 NSData。我发现这似乎有效：

Objective-C

目标-C

[NSString stringWithUTF8String:(char *)data.bytes];

Swift

迅速

[[NSString alloc] initWithBytes:(char *)data.bytes length:data.length encoding:NSUTF8StringEncoding];

回答by Gal

Just to summarize, here's a complete answer, that worked for me.

总结一下，这是一个完整的答案，对我有用。

My problem was that when I used

我的问题是当我使用

init?(data: Data, encoding: String.Encoding)

The string I got was unpredictable: Around 70% it did contain the expected value, but too often it resulted with Nullor even worse: garbaged at the end of the string.

我得到的字符串是不可预测的：大约 70% 它确实包含预期值，但它经常导致Null甚至更糟：在字符串末尾垃圾。

After some digging I switched to

经过一番挖掘，我切换到

import Foundation

let json = """
{
"firstName" : "John",
"lastName" : "Doe"
}
"""

let data = json.data(using: String.Encoding.utf8)!

let optionalString = String(data: data, encoding: String.Encoding.utf8)
print(String(describing: optionalString))

/*
 prints:
 Optional("{\n\"firstName\" : \"John\",\n\"lastName\" : \"Doe\"\n}")
*/

And got the expected result every time.

并且每次都得到了预期的结果。

回答by Imanou Petit

With Swift 5, you can use String's init(data:encoding:)initializer in order to convert a Datainstance into a Stringinstance using UTF-8. init(data:encoding:)has the following declaration:

在 Swift 5 中，您可以使用String的init(data:encoding:)初始化程序将Data实例转换为String使用 UTF-8的实例。init(data:encoding:)有以下声明：

##代码##

Returns a Stringinitialized by converting given data into Unicode characters using a given encoding.

返回String通过使用给定编码将给定数据转换为 Unicode 字符而初始化的。

The following Playground code shows how to use it:

以下 Playground 代码展示了如何使用它：

##代码##