本例是以高德地圖覆蓋物圓作為電子圍欄，通過給mapview添加的Tap事件確定圓的經緯度，滑動slider修改圓的半徑，來添加電子圍欄。

添加代理UIGestureRecognizerDelegate(為了解決點擊事件沖突)

- (void)viewDidLoad {
    UITapGestureRecognizer *tap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(tap:)];

    tap.delegate = self; //一定要記得設置代理

    [self.mapView addGestureRecognizer:tap];

//獲取上次設置的圈的經緯度和半徑
    self.circle = [MACircle circleWithCenterCoordinate:self.touchMapCoordinate radius:self.Rslider.value];
}

//允許多個交互事件
- (BOOL)gestureRecognizer:(UIGestureRecognizer *)gestureRecognizer shouldRecognizeSimultaneouslyWithGestureRecognizer:(UIGestureRecognizer *)otherGestureRecognizer {
    return YES;
}

//點擊事件
- (void)tap:(UITapGestureRecognizer *)tap
{
    //移除屏幕上的圓
    [self.mapView removeOverlay:self.circle];
    
    //保存點擊獲取的經緯度
    self.touchMapCoordinate =
    [self.mapView convertPoint:[tap locationInView:self.mapView] toCoordinateFromView:self.mapView];

    //設置圓的位置
    self.circle.coordinate = self.touchMapCoordinate;
    
    //反地理編碼獲取詳細地址
    [self getAddressByLatitude:self.touchMapCoordinate.latitude longitude:self.touchMapCoordinate.longitude];

    //顯示經緯度及半徑
    self.latitudeLb.text = [NSString stringWithFormat:@"%f", self.touchMapCoordinate.latitude];
    self.longitudeLb.text = [NSString stringWithFormat:@"%f", self.touchMapCoordinate.longitude];
    self.valueLabel.text = [NSString stringWithFormat:@"%.3f千米", self.Rslider.value/1000];

    //添加新圓到屏幕上
    [self.mapView addOverlay: self.circle];
}

//滑動slider改變圓的半徑(ValueChange)
- (IBAction)Rslider:(id)sender {
    self.valueLabel.text = [NSString stringWithFormat:@"%.3f千米", self.Rslider.value/1000];

    //移除屏幕上的圓
    [self.mapView removeOverlay:self.circle];
    self.circle = nil;

    //設置圓的半徑(經緯度由點擊事件獲取)
    self.circle = [MACircle circleWithCenterCoordinate:self.touchMapCoordinate radius:self.Rslider.value];

    //添加新圓到屏幕上
    [self.mapView addOverlay:self.circle];
}

最終效果