如何打印 NSValue 字节

Question

如何打印 NSValue 字节？使用 print 时，它不会打印所有字节并放入“...”。例如。 {长度 = 128，字节 = 0x00000000 0000f03f 00000000 00000000 ... 00000000 0000f03f }

import Cocoa
import SceneKit

var identityMatrix = SCNMatrix4()

identityMatrix.m11 = 1
identityMatrix.m12 = 0
identityMatrix.m13 = 0
identityMatrix.m14 = 0
identityMatrix.m21 = 0
identityMatrix.m22 = 1
identityMatrix.m23 = 0
identityMatrix.m24 = 0
identityMatrix.m31 = 0
identityMatrix.m32 = 0
identityMatrix.m33 = 1
identityMatrix.m34 = 0
identityMatrix.m41 = 0
identityMatrix.m42 = 0
identityMatrix.m43 = 0
identityMatrix.m44 = 1

var a = [NSValue]()

a.append(NSValue(scnMatrix4:identityMatrix))

identityMatrix.m11 = 1
identityMatrix.m12 = 0
identityMatrix.m13 = 0
identityMatrix.m14 = 0
identityMatrix.m21 = 0
identityMatrix.m22 = 1
identityMatrix.m23 = 0
identityMatrix.m24 = 0
identityMatrix.m31 = 0
identityMatrix.m32 = 0
identityMatrix.m33 = 1
identityMatrix.m34 = 0
identityMatrix.m41 = 0
identityMatrix.m42 = -1.0
identityMatrix.m43 = 0
identityMatrix.m44 = 1

a.append(NSValue(scnMatrix4:identityMatrix))

print(a[0])

Answer 1

首先，我们可以通过使用数组字面量和 SCNMatrix4 初始化程序来消除所有可变性：

import Cocoa
import SceneKit

let a = [
    SCNMatrix4(
        m11: 1, m12: 0, m13: 0, m14: 0,
        m21: 0, m22: 0, m23: 0, m24: 0,
        m31: 0, m32: 0, m33: 1, m34: 0,
        m41: 0, m42: 0, m43: 0, m44: 1
    ),
    SCNMatrix4(
        m11: 1, m12:  0, m13: 0, m14: 0,
        m21: 0, m22:  1, m23: 0, m24: 0,
        m31: 0, m32:  0, m33: 1, m34: 0,
        m41: 0, m42: -1, m43: 0, m44: 1
    ),
].map(NSValue.init(scnMatrix4:))

print(a[0])

这使代码更加合理。我们还可以从文档中注意到，已经有一个常量可以用来获取单位矩阵：

import Cocoa
import SceneKit

let a = [
    SCNMatrix4Identity,
    SCNMatrix4(
        m11: 1, m12:  0, m13: 0, m14: 0,
        m21: 0, m22:  1, m23: 0, m24: 0,
        m31: 0, m32:  0, m33: 1, m34: 0,
        m41: 0, m42: -1, m43: 0, m44: 1
    ),
].map(NSValue.init(scnMatrix4:))

print(a[0])

尚不清楚为什么这些矩阵包含在 NSValue 中，但要显示有关它们的详细信息（并调用它们的其他方法），您需要将矩阵从 NSValue 框使用 scnMatrix4Value API:

let sampleMatrix = a[0].scnMatrix4Value
print(sampleMatrix)

如果你想打印这些的字节布局，（尽管仍然不清楚你为什么想要这个，因为 AFAICT，NSValue 和 SCNMatrix4 没有对它们的内存布局做出任何承诺), 您可以使用通常的指针 APIs，结合一些十六进制打印逻辑，例如 this:

withUnsafeBytes(of: &sampleMatrix) { sampleMatrixPointer in
    print(sampleMatrixPointer.map { String(format: "%02x", [=13=]) }.joined(separator: ""))
}

打印：

000000000000f03f000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000f03f0000000000000000000000000000000000000000000000000000000000000000000000000000f03f

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