我有一个应用程序,加载一个有3个选项卡的选项卡控制器。其中之一是mapview。它通过以下代码设置为放大用户的位置:
- (void)viewWillAppear:(BOOL)animated{
[super viewWillAppear:animated];
_mapView.showsUserLocation = YES;
CLLocationCoordinate2D zoomLocation;
//IF no city was selected, use userLocation as center
if (!self.cityWasSelected) {
zoomLocation.latitude = self.userLocation.coordinate.latitude;
zoomLocation.longitude = self.userLocation.coordinate.longitude;
CLLocationDistance visibleDistance = 5000; // 5 kilometers
MKCoordinateRegion adjustedRegion = MKCoordinateRegionMakeWithDistance(zoomLocation, visibleDistance, visibleDistance);
[_mapView setRegion:adjustedRegion animated:YES];
} else { //if a city was selected, use that city's value...this is actually the same right now, since self.userLocation is set appropriately elsewhere.
//Set location from selection - forward geocode
zoomLocation.latitude = self.userLocation.coordinate.latitude;
zoomLocation.longitude = self.userLocation.coordinate.longitude;
CLLocationDistance visibleDistance = 5000; // 5 kilometers
MKCoordinateRegion adjustedRegion = MKCoordinateRegionMakeWithDistance(zoomLocation, visibleDistance, visibleDistance);
[_mapView setRegion:adjustedRegion animated:YES];
}
}
第一个标签是用于用户偏好的tableviewcontroller,第二个标签是mapview,第三个标签是tableview。当我第一次点击mapview,地图显示了整个世界:)如果我点击回到初始标签或列表标签,然后返回到mapview,地图是正确的中心围绕我当前的位置。
为什么会发生这种情况?
在地图视图中设置showsUserLocation
将开始搜索用户的位置。这是一个异步操作,您不能假设在将showsUserLocation
设置为YES后mapView.userLocation
将立即有效。
第一次出现视图时,要求地图视图开始定位。mapView.userLocation
可能返回nil。第二次时,地图视图可能最终获得了用户位置并成功加载了地图区域。这是纯粹的运气,你不应该指望你会第二次获得位置(它可能会失败,花费比平常更长的时间)。
当地图视图确定了用户位置,它会回调一个委托方法(MKMapViewDelegate)。你需要像这样实现这个委托方法:
- (void)mapView:(MKMapView *)mapView didUpdateUserLocation:(MKUserLocation *)userLocation {
// We have location, do your logic of setting the map region here.
...
}