title: How can i change the NSArray to MKPolyline polylineWithCoordinates compatible type？
body: <p>I add a NSTimer to record the location from location manager ,and put ever location into a NSMutableArray.</p>
  
  <pre><code>-(void)OnTimer:(NSTimer *)param{
       [self.locationRecoder addObject:self.manager.location];
  }
  </code></pre>
  
  <p>and I add a button to UI, when I click the button, it invoke this method</p>
  
  <pre><code>-(IBAction)Click:(id)sender(){
     NSArray *coordinateArray = [self.locationRecorder valueForKeyPath:@"coordinate"];
     MKPolyline *lines = [MKPolyline ploylineWithCoordinates:(CLLocationCoordinate2D *)coordinateArray count:coordinateArray.count];
     [self.map addOverlay:lines];
  }
  </code></pre>
  
  <p>then there is nothing drawn. did i do something wrong in type cast?</p>