循环访问数据库中的坐标数组时出现问题

Question

我可以解析数据库中的数据，但很难循环遍历数据库中的所有坐标并将它们绘制在地图视图上。有人可以帮忙吗？

-(void)scanDatabase{

  UIDevice *device = [UIDevice currentDevice];
  NSString *uid = [device uniqueIdentifier];
  NSString *myUrl = [NSString stringWithFormat:@"http://address.php?uid=%@",uid];
  NSData *dataURL =  [NSData dataWithContentsOfURL: [ NSURL URLWithString: myUrl ]];    

  // to receive the returend value
  NSString *serverOutput =[[NSString alloc] initWithData:dataURL encoding:NSUTF8StringEncoding];
  NSArray *components = [serverOutput componentsSeparatedByString:@"\n"];

  for (NSString *line in components) {
    NSArray *fields = [line componentsSeparatedByString:@"\t"];
    [eventPoints addObjectsFromArray:fields];

    int count = [fields count];
    for(int i=0;i < count; i++) {
      int myindex0 = i*count;
      int myindex1 = (i*count)+1;
      int myindex2 = (i*count)+2;

      NSString *mytitle = [eventPoints objectAtIndex:myindex0];
      NSNumber *myLat = [eventPoints objectAtIndex:myindex1];
      NSNumber *myLon = [eventPoints objectAtIndex:myindex2];

      CLLocationCoordinate2D loc;

      loc.latitude = myLat.doubleValue;
      loc.longitude = myLon.doubleValue;

      customAnnotation *event = [[customAnnotation alloc] initWithCoordinate:loc];
      event.title = mytitle;

      MKPinAnnotationView *newAnnotationPin = [[MKPinAnnotationView alloc] initWithAnnotation:event reuseIdentifier:@"simpleAnnotation"];
      newAnnotationPin.pinColor = MKPinAnnotationColorRed;

      [map addAnnotation:event];
    }
  }
}

Answer 1

您需要使用委托方法来添加注释视图，

- (MKAnnotationView *)mapView:(MKMapView *)mapView viewForAnnotation:(id <MKAnnotation>)annotation

否则它永远不会出现，请参阅此处
http://developer.apple.com/library/ios/#documentation/MapKit/Reference/MKMapViewDelegate_Protocol/MKMapViewDelegate/MKMapViewDelegate.html

- (MKAnnotationView *)mapView:(MKMapView *)mapView viewForAnnotation:(id <MKAnnotation>)annotation
{
    MKPinAnnotationView *newAnnotationPin = [[[MKPinAnnotationView alloc] initWithAnnotation:annotation reuseIdentifier:@"simpleAnnotation"] autorelease];
        newAnnotationPin.pinColor = MKPinAnnotationColorRed;
    return newAnnotationPin;
}

Answer 2

不太确定您遇到了什么问题，因为“很难过......”并没有很好地描述它们:-)

看看您的代码，我喜欢做出以下评论：

• 内部循环似乎没有做出任何事情感觉。
• 为什么不直接访问这些字段？
• myLat 和 myLon 应该是 NSString 对象引用。

也许这样的方法效果更好：

-(void)scanDatabase{

  UIDevice *device = [UIDevice currentDevice];
  NSString *uid = [device uniqueIdentifier];
  NSString *myUrl = [NSString stringWithFormat:@"http://address.php?uid=%@",uid];
  NSData *dataURL =  [NSData dataWithContentsOfURL: [ NSURL URLWithString: myUrl ]];    

  // to receive the returend value
  NSString *serverOutput =[[NSString alloc] initWithData:dataURL encoding:NSUTF8StringEncoding];
  NSArray *components = [serverOutput componentsSeparatedByString:@"\n"];

  for (NSString *line in components) {
    NSArray *fields = [line componentsSeparatedByString:@"\t"];
    [eventPoints addObjectsFromArray:fields];

    if ( [fields count] != 3 ) {
      // something is wrong/unexpected here, act appropriately
    }
    else {
      NSString *mytitle = [fields objectAtIndex:0];
      NSString *myLat = [fields objectAtIndex:1];
      NSString *myLon = [fields objectAtIndex:2];

      CLLocationCoordinate2D loc;

      loc.latitude = myLat.doubleValue;
      loc.longitude = myLon.doubleValue;

      customAnnotation *event = [[customAnnotation alloc] initWithCoordinate:loc];
      event.title = mytitle;

      MKPinAnnotationView *newAnnotationPin = [[MKPinAnnotationView alloc] initWithAnnotation:event reuseIdentifier:@"simpleAnnotation"];
      newAnnotationPin.pinColor = MKPinAnnotationColorRed;

      [map addAnnotation:event];
    }
  }
}