如何将NSArray更改为MKPolyline polylineWithCoordinates兼容类型？ [英] How can i change the NSArray to MKPolyline polylineWithCoordinates compatible type？

问题描述

我添加了一个NSTimer来记录位置管理器的位置，并将所有位置放入NSMutableArray。

I add a NSTimer to record the location from location manager ,and put ever location into a NSMutableArray.

-(void)OnTimer:(NSTimer *)param{
     [self.locationRecoder addObject:self.manager.location];
}

我向UI添加一个按钮，当我点击按钮时，它会调用这个方法

and I add a button to UI, when I click the button, it invoke this method

-(IBAction)Click:(id)sender(){
   NSArray *coordinateArray = [self.locationRecorder valueForKeyPath:@"coordinate"];
   MKPolyline *lines = [MKPolyline ploylineWithCoordinates:(CLLocationCoordinate2D *)coordinateArray count:coordinateArray.count];
   [self.map addOverlay:lines];
}

然后没有画出来。我在打字时做错了什么？

then there is nothing drawn. did i do something wrong in type cast?

推荐答案

polylineWithCoordinates 方法需要一个简单的C数组结构 CLLocationCoordinate2D 。

The polylineWithCoordinates method requires a plain C array of structs of type CLLocationCoordinate2D.

调用 valueForKeyPath之后， coordinateArray 是一个 NSArray NSValue 对象。

这与C数组结构不同。

After the call to valueForKeyPath, coordinateArray is an NSArray of NSValue objects.
That is not the same thing as a C array of structs.

转换 NSArray 到（CLLocationCoordinate2D *）不会将其转换为结构的C数组。

Casting that NSArray to (CLLocationCoordinate2D *) doesn't convert it to a C array of structs.

相反，您必须使用 malloc 手动创建C数组并循环遍历 locationRecoder 数组：

Instead, you have to create the C array manually using malloc and looping through the locationRecoder array:

CLLocationCoordinate2D *coordinateArray 
    = malloc(sizeof(CLLocationCoordinate2D) * locationRecorder.count);

int caIndex = 0;
for (CLLocation *loc in locationRecorder) {
    coordinateArray[caIndex] = loc.coordinate;
    caIndex++;
}

MKPolyline *lines = [MKPolyline polylineWithCoordinates:coordinateArray 
                        count:locationRecorder.count];

free(coordinateArray);

[self.map addOverlay:lines];

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