讓地圖視圖自適應線路

在 百度MapKit SDK 中的線路中有一個方法：

//根據polyline設置地圖範圍
- (void)mapViewFitPolyLine:(BMKPolyline *) polyLine {
    CGFloat ltX, ltY, rbX, rbY;
    if (polyLine.pointCount < 1) {
        return;
    }
    BMKMapPoint pt = polyLine.points[0];
    ltX = pt.x, ltY = pt.y;
    rbX = pt.x, rbY = pt.y;
    for (int i = 1; i < polyLine.pointCount; i++) {
        BMKMapPoint pt = polyLine.points[i];
        if (pt.x < ltX) {
            ltX = pt.x;
        }
        if (pt.x > rbX) {
            rbX = pt.x;
        }
        if (pt.y > ltY) {
            ltY = pt.y;
        }
        if (pt.y < rbY) {
            rbY = pt.y;
        }
    }
    BMKMapRect rect;
    rect.origin = BMKMapPointMake(ltX , ltY);
    rect.size = BMKMapSizeMake(rbX - ltX, rbY - ltY);
    [_mapView setVisibleMapRect:rect];
    _mapView.zoomLevel = _mapView.zoomLevel - 0.3;
}

經過調用執行該方法，可讓地圖自適應的顯示線路，地圖視圖自動縮放一個較好的level來顯示當前的整個線路圖，而不用本身去人爲設置level。