Google map with multiple annotations

Question

我是新手google地圖我跟着下面的教程https://developers.google.com/maps/documentation/ios-sdk/marker當我嘗試使用for循環顯示多個註釋時，我得到了一個註釋。以下是我的代碼，

for (int i = 0; i < [ARR count]; i++) 
{ 
    float latitude_val = [[NSString stringWithFormat:@"%@",[[ARR objectAtIndex:i] valueForKey:@"lat"]] floatValue]; 
    float longitude_val = [[NSString stringWithFormat:@"%@",[[ARR:i] valueForKey:@"lng"]] floatValue];    
    GMSMarker *marker = [[GMSMarker alloc] init]; 
    marker.position = CLLocationCoordinate2DMake(latitude_val, longitude_val);   
    marker.map = _mapView;  
} 

感謝