Question

我创建了一个不断读取当前用户坐标的应用程序，并将它们存储在SQLite数据库中我有一个显示在整个屏幕上的地图。
现在我想在用户移动时在地图上画一条线我已经创造了这一切问题是我不能让它成为一个“活着”。叠加层未更新。
这是逻辑：
在ViewDidLoad中我有

...
if (nil != self.routeLine) {
        [self.mapView addOverlay:self.routeLine];
    }

在处理每个新坐标的函数中：

...
NSString* coordinate = [NSString stringWithFormat:@"%f,%f", thisLocation.longitude, thisLocation.latitude];
            [self.paths addObject:coordinate];

MKMapPoint northEastPoint;
    MKMapPoint southWestPoint;

    // create a c array of points.
    MKMapPoint* pointArr = malloc(sizeof(CLLocationCoordinate2D) * self.paths.count);

    for(int idx = 0; idx < self.paths.count; idx++)
    {
        // break the string down even further to latitude and longitude fields.
        NSString* currentPointString = [self.paths objectAtIndex:idx];
        NSArray* latLonArr = [currentPointString componentsSeparatedByCharactersInSet:[NSCharacterSet characterSetWithCharactersInString:@","]];

        CLLocationDegrees latitude  = [[latLonArr objectAtIndex:1] doubleValue];
        CLLocationDegrees longitude = [[latLonArr objectAtIndex:0] doubleValue];

        // create our coordinate and add it to the correct spot in the array
        CLLocationCoordinate2D coordinate = CLLocationCoordinate2DMake(latitude, longitude);


        MKMapPoint point = MKMapPointForCoordinate(coordinate);

        // adjust the bounding box
        // if it is the first point, just use them, since we have nothing to compare to yet.
        if (idx == 0) {
            northEastPoint = point;
            southWestPoint = point;
        }
        else
        {
            if (point.x > northEastPoint.x)
                northEastPoint.x = point.x;
            if(point.y > northEastPoint.y)
                northEastPoint.y = point.y;
            if (point.x < southWestPoint.x)
                southWestPoint.x = point.x;
            if (point.y < southWestPoint.y)
                southWestPoint.y = point.y;
        }

        pointArr[idx] = point;
    }

    // create the polyline based on the array of points.
    self.routeLine = [MKPolyline polylineWithPoints:pointArr count:self.paths.count];

    _routeRect = MKMapRectMake(southWestPoint.x, southWestPoint.y, northEastPoint.x - southWestPoint.x, northEastPoint.y - southWestPoint.y);
    // clear the memory allocated earlier for the points
    free(pointArr);

这是viewForOverlay委托函数：

- (MKOverlayView *)mapView:(MKMapView *)mapView viewForOverlay:(id <MKOverlay>)overlay
{
    MKOverlayView* overlayView = nil;

    if(overlay == self.routeLine)
    {
        //if we have not yet created an overlay view for this overlay, create it now.
        if(nil == self.routeLineView)
        {
            self.routeLineView = [[MKPolylineView alloc] initWithPolyline:self.routeLine];
            self.routeLineView.fillColor = [UIColor blueColor];
            self.routeLineView.strokeColor = [UIColor blueColor];
            self.routeLineView.lineWidth = 5;
        }

        overlayView = self.routeLineView;
    }
    return overlayView;
}

Answer 1

在viewDidLoad中，代码使用addOverlay调用self.routeLine，我假设它最初设置为先前保存的坐标。

地图视图将MKPoyline点routeLine添加到其内部叠加层列表中并绘制叠加层。

然后，在处理每个新坐标＆＃34;的＆＃34;函数中，self.routeLine更改为指向 new MKPolyline。

地图未更新叠加视图的原因是地图视图仍在使用调用MKPolyline时传递给它的原始 addOverlay。

由于MKPolyline本身不可变（它不允许在创建后更改点/坐标列表），因此有两个主要选项：

删除现有的叠加层并添加一个带有更新坐标的新叠加层。这是最简单的选择。将self.routeLine设置为新MKPolyline后，请执行以下操作（例如）：
```
[self.mapView removeOverlays:mapView.overlays];
self.routeLineView = nil;
[self.mapView addOverlay:self.routeLine];
```
这种简单方法的主要缺点是，如果频繁更新或叠加层很大或很复杂，叠加层似乎会闪烁。
另一种方法是创建一个可变的自定义叠加层和叠加层视图，使您能够更快速，更顺畅地动态刷新叠加层。
幸运的是，Apple has provided a sample app called Breadcrumb就是这样做的。

Answer 2

也许您忘了拨打[self.view setNeedsDisplay]？

UIView docs

MapKit上绘制路径的问题

2 个答案: