QGroundMap动态绘制MapPolyline异常：Instantiator使用问题求助

我在重写QGroundMap时遇到了问题：需要在自定义QGround控件的QGroundMap上动态绘制多个MapPolyline对象，目前仅能通过直接注入的方式实现：

Component.onCompleted: {
    objMgr.createObjects([mapLine], _root.mapControl, true /* parentObjectIsMap */)
}

标准的MapItemView及其他元素无法正常工作，尝试用Instantiator实例化多个MapPolyline也失败了：

Instantiator {
    id: testInstantiator
    model: globalCoordinates

    function getIndex(index) {
        console.log("currentIndexIs")
        console.log(index)
        return index
    }

    delegate: Component {
        id: mapLine

        MapPolyline {
            id: targetPolyLine
            line.width: 3
            line.color: "red"
            z: QGroundControl.zOrderWaypointLines
            path: testInstantiator.model[index]
        }
    }
}

我的坐标模型定义如下：

property var globalCoordinates: [
        [QtPositioning.coordinate(42, 13), QtPositioning.coordinate(42, 18)],
        [QtPositioning.coordinate(42, 13), QtPositioning.coordinate(42, 20)],
        [QtPositioning.coordinate(42, 13), QtPositioning.coordinate(42, 22)],
        [QtPositioning.coordinate(42, 13), QtPositioning.coordinate(42, 24)],
        [QtPositioning.coordinate(42, 13), QtPositioning.coordinate(42, 26)]
    ]

只有把index替换成具体数字时，才能绘制出单条线：

Instantiator {
    id: testInstantiator
    model: globalCoordinates

    function getIndex(index) {
        console.log("currentIndexIs")
        console.log(index)
        return index
    }

    delegate: Component {
        id: mapLine

        MapPolyline {
            id: targetPolyLine
            line.width: 3
            line.color: "red"
            z: QGroundControl.zOrderWaypointLines
            path: testInstantiator.model[1] // 仅能绘制单条线
        }
    }
}

解决方法 #

1. 修复Instantiator的数据源引用问题

在QML的Instantiator delegate上下文里，当模型是数组类型时，modelData会直接指向当前循环的数组项，不需要通过testInstantiator.model[index]获取。同时，delegate内的index是上下文自带的属性，不需要额外定义getIndex函数。修正后的代码：

Instantiator {
    id: testInstantiator
    model: globalCoordinates

    delegate: Component {
        MapPolyline {
            line.width: 3
            line.color: "red"
            z: QGroundControl.zOrderWaypointLines
            path: modelData // 直接使用当前项数据
        }
    }
}

2. 确保MapPolyline正确挂载到MapControl

如果上述代码仍不生效，需要显式指定MapPolyline的父对象为QGroundMap的mapControl，确保它被正确添加到地图控件中：

Instantiator {
    id: testInstantiator
    model: globalCoordinates

    delegate: Component {
        MapPolyline {
            parent: _root.mapControl // 显式绑定到地图控件
            line.width: 3
            line.color: "red"
            z: QGroundControl.zOrderWaypointLines
            path: modelData
        }
    }
}

3. 替代方案：使用Repeater

Repeater在QML中更适合用于重复创建可视元素，稳定性优于Instantiator，代码如下：

Repeater {
    model: globalCoordinates
    delegate: MapPolyline {
        parent: _root.mapControl
        line.width: 3
        line.color: "red"
        z: QGroundControl.zOrderWaypointLines
        path: modelData
    }
}

4. 验证模型数据有效性

可以在组件加载完成时打印坐标数据，确保所有QtPositioning.coordinate对象都正确初始化：

Component.onCompleted: {
    globalCoordinates.forEach((path, idx) => {
        console.log(`路径 ${idx} 坐标:`, path)
    })
}

内容的提问来源于stack exchange，提问作者Nazarii Muliak