ios - 如何获取 CGPDFDictionaryRef 键

Question

我想获取 CGPDFDictionaryRef 的所有键。到目前为止我发现的是from stackoverflow

这是我在 swift 中的代码:

 func printPDFKeys(key: UnsafePointer<Int8>, ob: CGPDFObjectRef, info: UnsafeMutablePointer<()>) -> Void{

 NSLog("key = %s", key);
   //return (key, ob , info)
  }

然后像这样调用这个函数。

     let myDoc = CGPDFDocumentCreateWithURL(url)
    if myDoc != nil {
    let myCatalog=CGPDFDocumentGetCatalog(myDoc)

       CGPDFDictionaryApplyFunction(myCatalog, printPDFKeys, nil);//Compiler error here
     }

但是我收到一个错误

a c function pointer can only be formed from a reference to a 'func' or a literal closure

我也试过像这样使用闭包:

var printPDFKeys: (  UnsafePointer<Int8>, CGPDFObjectRef,  UnsafeMutablePointer<()> )-> Void

    printPDFKeys={
        key,ob,info in

    NSLog("key = %s", key);

    }

我仍然遇到同样的错误。我该怎么做

Answer 1

正确的闭包语法是:

CGPDFDictionaryApplyFunction(myCatalog, { (key, object, info) -> Void in
// do something
}, nil)