尝试读取属性

Question

您好我正在尝试开始在iOS上学习一些与swift相结合的金属。目前我只是想让应用程序使用CAMetalLayer而不是普通的CALayer打开自定义UIView。我在以下行收到BAD_ACCESS错误：self.metalLayer.device = self.device 以下代码是UIView的子类，它是从故事板而不是普通的UIView加载的。我正在遵循以下示例，它是在Objective-C中，我试图在swift中实现相同的目标。现在有点亏本。有什么想法吗？

import UIKit
import Metal

class MBEMetalView: UIView {

    var device: MTLDevice

    var metalLayer: CAMetalLayer {
        return CAMetalLayer(layer: self.layer)
    }

    override class func layerClass() -> AnyClass {
        return CAMetalLayer.self
    }

    required init?(coder aDecoder: NSCoder) {
        self.device = MTLCreateSystemDefaultDevice()!
        super.init(coder: aDecoder)


        self.metalLayer.device = self.device
        self.metalLayer.pixelFormat = MTLPixelFormat.BGRA8Unorm

    }

    override func didMoveToWindow() {
        self.redraw()
    }

    func redraw() {
        var drawable: CAMetalDrawable? = self.metalLayer.nextDrawable()
        var texture: MTLTexture? = drawable?.texture

        var passDescriptor: MTLRenderPassDescriptor = MTLRenderPassDescriptor.self()
        passDescriptor.colorAttachments[0].texture = texture
        passDescriptor.colorAttachments[0].loadAction = MTLLoadAction.Clear
        passDescriptor.colorAttachments[0].storeAction = MTLStoreAction.Store
        passDescriptor.colorAttachments[0].clearColor = MTLClearColor.init(red: 1, green: 0, blue: 0, alpha: 1)

        var commandQueue: MTLCommandQueue = self.device.newCommandQueue()

        var commandBuffer: MTLCommandBuffer = commandQueue.commandBuffer()

        var commandEncoder: MTLCommandEncoder = commandBuffer.renderCommandEncoderWithDescriptor(passDescriptor)
        commandEncoder.endEncoding()

        commandBuffer.presentDrawable(drawable!)
        commandBuffer.commit()
    }

}

@alex_p告诉我，我每次调用metalLayer的readonly可计算函数都给了我一个新的CAMetalLayer，所以我改变了我的代码，但现在我得到了以下SIGABRT错误 以下行/BuildRoot/Library/Caches/com.apple.xbs/Sources/Metal/Metal-55.1.1/ToolsLayers/Debug/MTLDebugDevice.mm:629: failed assertion "iosurface must not be nil."：var drawable: CAMetalDrawable? = self.metalLayer.nextDrawable()

我目前的代码是：

import UIKit
import Metal

class MBEMetalView: UIView {

    var device: MTLDevice? = MTLCreateSystemDefaultDevice()
    var metalLayer: CAMetalLayer = CAMetalLayer()
    var commandQueue: MTLCommandQueue! = nil

    override class func layerClass() -> AnyClass {
        return CAMetalLayer.self
    }

    required init?(coder aDecoder: NSCoder) {
        self.commandQueue = self.device!.newCommandQueue()

        super.init(coder: aDecoder)

        self.metalLayer.device = self.device
        self.metalLayer.pixelFormat = MTLPixelFormat.BGRA8Unorm

    }

    override func didMoveToWindow() {
        self.redraw()
    }

    func redraw() {
        var drawable: CAMetalDrawable? = self.metalLayer.nextDrawable()
        let texture: MTLTexture? = drawable!.texture

        let passDescriptor: MTLRenderPassDescriptor = MTLRenderPassDescriptor.self()
        passDescriptor.colorAttachments[0].texture = texture
        passDescriptor.colorAttachments[0].loadAction = MTLLoadAction.Clear
        passDescriptor.colorAttachments[0].storeAction = MTLStoreAction.Store
        passDescriptor.colorAttachments[0].clearColor = MTLClearColor.init(red: 1, green: 0, blue: 0, alpha: 1)

        let commandBuffer: MTLCommandBuffer = commandQueue.commandBuffer()

        let commandEncoder: MTLCommandEncoder = commandBuffer.renderCommandEncoderWithDescriptor(passDescriptor)
        commandEncoder.endEncoding()

        commandBuffer.presentDrawable(drawable!)
        commandBuffer.commit()
    }

}