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轨迹的渐变折线渲染正常，但是地图缩放的时候会崩溃。单色轨道线工作正常。可能是什么问题呢？

私人 func addPolyline() {

    if (mapView?.style?.source(withIdentifier: "polyline") as? MGLShapeSource) == nil {
        
        guard let style = mapView?.style else {return}
        //let source = MGLShapeSource(identifier: "polyline", shape: nil, options: nil)
        let source = MGLShapeSource(identifier: "polyline", shape: nil, options: [.lineDistanceMetrics: true])
        style.addSource(source)
        polylineSource = source
        
        // Add a layer to style our polyline.
        let layer = MGLLineStyleLayer(identifier: "polyline", source: source)
        layer.lineJoin = NSExpression(forConstantValue: "round")
        layer.lineCap = NSExpression(forConstantValue: "round")
        layer.lineColor = NSExpression(forConstantValue: UIColor.init(cgColor: #colorLiteral(red: 0.9372549057, green: 0.3490196168, blue: 0.1921568662, alpha: 1)))
        let stops =   [0: UIColor.red,
                           0.1: UIColor.yellow,
                           0.3: UIColor.green,
                           0.5: UIColor.cyan,
                           0.7: UIColor.systemBlue,
                           1: UIColor.blue]

        //FIXME: - CRACH when adding this line when zooming !!!!!!!!!!!!!

        layer.lineGradient = NSExpression(format: "mgl_interpolate:withCurveType:parameters:stops:($lineProgress, 'linear', nil, %@)", stops)

        
        // The line width should gradually increase based on the zoom level.
        layer.lineWidth = NSExpression(format: "mgl_interpolate:withCurveType:parameters:stops:($zoomLevel, 'linear', nil, %@)",[13: 2, 18: 5])
        style.addLayer(layer)
    }
}
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