ios7 - 使用 Swift 的 MKPolygon(调用中参数 'interiorPolygons' 缺少参数)

Question

各位开发者，我正在尝试在 mapview 上实现多边形叠加层，如下所示:

private func drawOverlayForObject(object: MyStruct) {
    if let coordinates: [CLLocationCoordinate2D] = object.geometry?.coordinates {
        let polygon = MKPolygon(coordinates: coordinates, count: coordinates.count)
        self.mapView.addOverlay(polygon)
    }
}

出现以下错误:

Missing argument for parameter 'interiorPolygons' in call

根据文档: Apple Docu:

Mutable Pointers

When a function is declared as taking an UnsafeMutablePointerargument, it can accept any of the following:

• nil, which is passed as a null pointer
• An UnsafeMutablePointer value
• An in-out expression whose operand is a stored lvalue of type Type, which is passed as the address of the lvalue
• An in-out [Type] value, which is passed as a pointer to the start of the array, and lifetime-extended for the duration of the call

现在我认为我的方法是正确的，提供一个 [CLLocationCoordinate2D] 数组。有没有人遇到同样的问题并找到解决方法？

谢谢罗尼

Answer 1

您收到的错误是 Swift 的隐晦方式，表示它找不到与您的参数匹配的方法。如果您确实尝试传递 interiorPolygons 参数，您会得到同样令人困惑的信息:

Extra argument 'interiorPolygons' in call

虽然您的代码非常接近；你只需要做一些小的改动。在您引用的文档中，它说您可以传递的其中一件事是:

An in-out [Type] value, which is passed as a pointer to the start of the array, and lifetime-extended for the duration of the call

因此，它正在寻找 in-out parameter .这是通过传递以 & 为前缀的 coordinates 来完成的，如下所示:

MKPolygon(coordinates: &coordinates, count: coordinates.count)

但是，输入输出参数不能是常量。来自文档:

You can only pass a variable as the argument for an in-out parameter. You cannot pass a constant or a literal value as the argument, because constants and literals cannot be modified.

因此，您需要先使用 var 定义 coordinates:

if var coordinates: [CLLocationCoordinate2D] = object.geometry?.coordinates

这使得整个函数看起来像这样:

private func drawOverlayForObject(object: MyStruct) {
    if var coordinates: [CLLocationCoordinate2D] = object.geometry?.coordinates {
        let polygon = MKPolygon(coordinates: &coordinates, count: coordinates.count)
        self.mapView.addOverlay(polygon)
    }
}