iOS 使用百度地图，仿滴滴打车的定位方法。拖动时时定位

这里的思路： 
（1）把图片放到屏幕的中间，这样在拖动的时候就不会跟随着地图移动了。 
（2）百度地图提供了，View坐标和地理坐标转换的方法。正式这个方法的存在，方便我们及时的获取拖动后的，屏幕中间的图片所在位置的经纬度。

当拖动地图的时候，定位的图片一直在屏幕的中央，当拖动停止的时候会显示出具体的信息

#import "HouseTypeMapVC.h"

@interface HouseTypeMapVC ()<BMKMapViewDelegate,BMKLocationServiceDelegate,BMKGeoCodeSearchDelegate>{

    BMKLocationService * _locService;

}
@property (nonatomic,strong) UIView * locationView;
@property (nonatomic,strong) UIImageView * locImageView;
@property (nonatomic,strong) UIView * messageView;
@property (nonatomic,strong) UILabel * addressLabel;
@property (nonatomic,strong) UIButton * sureButton;
@property (nonatomic,strong) NSString * name;
@property (nonatomic,assign) CLLocationCoordinate2D location2D;

@property (nonatomic, strong)BMKGeoCodeSearch* searchAddress;
@property (strong, nonatomic) IBOutlet BMKMapView *mapView;
@property (nonatomic,strong)BMKUserLocation *userLocation; //定位功能
@end

@implementation HouseTypeMapVC

-(void)viewWillAppear:(BOOL)animated{

    [super viewWillAppear: animated];
    [_mapView viewWillAppear];
    _mapView.delegate = self; // 此处记得不用的时候需要置nil，否则影响内存的释放
    _locService.delegate = self;
}

-(void)viewWillDisappear:(BOOL)animated{
    [_mapView viewWillDisappear];
    _mapView.delegate = nil; // 不用时，置nil
    _locService.delegate = nil;
}

- (void)viewDidLoad {
    [super viewDidLoad];
}

- (void)initUI{
    [self goBackBtn];
     _mapView.mapType=BMKMapTypeStandard;
    [self initlocationService];

}

#pragma mark --initlocationService--定位

-(void)initlocationService{

    _locService = [[BMKLocationService alloc]init];

    [_locService startUserLocationService];
    _mapView.showsUserLocation = NO;//先关闭显示的定位图层
    _mapView.userTrackingMode = BMKUserTrackingModeNone;//设置定位的状态
    _mapView.showsUserLocation = YES;//显示定位图层
    _mapView.showMapScaleBar = YES;//显示比例尺
    _mapView.zoomLevel = 17;//地图显示的级别

    _searchAddress = [[BMKGeoCodeSearch alloc]init];
    _searchAddress.delegate = self;

}

//这里是创建中心显示的图片和显示详细地址的View

- (void)createLocationSignImage{

    //LocationView定位在当前位置，换算为屏幕的坐标，创建的定位的图标

    self.locationView = [[UIView alloc]initWithFrame:CGRectMake(0, 0, 28, 35)];
    self.locImageView = [[UIImageView alloc]initWithFrame:CGRectMake(0, 0, 28, 35)];
    self.locImageView.image = [UIImage imageNamed:@"myLocation"];
    [self.locationView addSubview:self.locImageView];

    //messageView 展示定位信息的View和Label和button

    self.messageView = [[UIView alloc]init];
    self.messageView.backgroundColor = [UIColor whiteColor];

    //把当前定位的经纬度换算为了View上的坐标

    CGPoint point = [self.mapView convertCoordinate:_mapView.centerCoordinate toPointToView:_mapView];

    //当解析出现错误的时候，会出现超出屏幕的情况，一种是大于了屏幕，一种是小于了屏幕
    if(point.x > ScreenWidth || point.x < ScreenWidth/5){

        point.x = _mapView.centerX;
        point.y = _mapView.centerY-64;

    }

    NSLog(@"Point------%f-----%f",point.x,point.y);
    //重新定位了LocationView

    self.locationView.center = point;

    [self.locationView setFrame:CGRectMake(point.x-14, point.y-18, 28, 35)];

    //重新定位了messageView
    [self.messageView setFrame:CGRectMake(30, point.y-40-20, SCREEN_WIDTH-60, 40)];

    //展示地址信息的label
    self.addressLabel = [[UILabel alloc]initWithFrame:CGRectMake(10, 0, self.messageView.frame.size.width - 80, 40)];

    self.addressLabel.font = [UIFont systemFontOfSize:13.0f];

    [self.messageView addSubview:self.addressLabel];

    //把地址信息传递到上个界面的button

    self.sureButton = [[UIButton alloc]initWithFrame:CGRectMake(self.addressLabel.frame.origin.x + self.addressLabel.frame.size.width, 0,self.messageView.frame.size.width - self.addressLabel.frame.origin.x - self.addressLabel.frame.size.width, 40)];

    [self.messageView addSubview:self.sureButton];

    self.sureButton.backgroundColor = [UIColor colorWithHex:0x2ecb7d];

    [self.sureButton setTitle:@"确定" forState:UIControlStateNormal];

    self.sureButton.titleLabel.font = [UIFont systemFontOfSize:13.0f];

    [self.sureButton setTitleColor:[UIColor whiteColor] forState:UIControlStateNormal];

    [self.sureButton addTarget:self action:@selector(sureButtonClick:) forControlEvents:UIControlEventTouchUpInside];

    [self.mapView addSubview:self.messageView];

    [