在Swift中调用CGPatternCreate

我想知道如何将下面的Objective-C方法转换为Swift函数？

CGPatternRef pattern = CGPatternCreate(NULL, rect, CGAffineTransformIdentity, 24, 24, kCGPatternTilingConstantSpacing, true, &callbacks); 

我的代码：

  let callbacks : CGPatternCallbacks = CGPatternCallbacks(version: 0) let pattern : CGPatternRef = CGPatternCreate(nil, rect, CGAffineTransformIdentity, 24, 24, kCGPatternTilingConstantSpacing, true, callbacks) 

但是我收到一条错误消息：

“CGPatternCallbacks”不能转换为“CConstPointer”

有没有这样的示例代码？ 谢谢

Answer 1

就是这样

 var callbacks : CGPatternCallbacks = CGPatternCallbacks(version: 0) var pattern = CGPatternCreate(nil, rect, CGAffineTransformIdentity, 24, 24, kCGPatternTilingConstantSpacing, true, &callbacks) 

Answer 2

这个解决scheme是有问题的：

在CGPatternCallbacks中注册的指针（对于绘制模式的函数）应该是CFunctionPointer <（UnsafeMutablePointer，CGContext>） – > Void）这意味着函数指针应该被转换为UnasfeMutablePointer，然后转换为COpaquePointer，然后转换为CFuncfionPointer

仍然无论如何，我得到函数调用exception，有一个简单的解决scheme：[ http://www.raywenderlich.com/90695/modern-core-graphics-with-swift-part-3%5D [1 ]

Answer 3

1. 选项1

    //global function - outside of the class func myDrawColoredPattern(info: UnsafeMutablePointer<Void>, context: CGContextRef?) -> Void { //draw pattern using context.... } var callbacks : CGPatternCallbacks = CGPatternCallbacks(version: 0, drawPattern: myDrawColoredPattern, releaseInfo: nil) let pattern: CGPatternRef? = CGPatternCreate(nil, rect, CGAffineTransformIdentity, 24, 24, CGPatternTiling.ConstantSpacing, true, &callbacks) 

2. 选项2 – “快捷”的方式

    let drawPattern: CGPatternDrawPatternCallback = { (_, context) in //draw pattern using context... } var callbacks = CGPatternCallbacks(version: 0, drawPattern: drawPattern, releaseInfo: nil) let pattern: CGPatternRef? = CGPatternCreate(nil, rect, CGAffineTransformIdentity, 24, 24, CGPatternTiling.ConstantSpacing, true, &callbacks)