QGis二次开发-保存矢量图形和字段

1、首先拿到shp图层

QgsVectorLayer *currentLayer = qobject_cast<QgsVectorLayer *>(MainWindow::TheInstance()->getActiveMapCanvas()->currentLayer());

2、生成矢量对象

//保存点
QgsPoint point(x,y,z);
//保存线 或面 其中QgsPolyline由QgsPoint 的点集组成
QgsPolyline Poly;
//QgsPolyline往塞点
poly.append(point);

3、生成几何对象,如果shp是三维的,hasM和hasZ是必须的,没有这一步会导致图层损坏

//点
QgsGeometry Geo = QgsGeometry::fromPointXY(QgsPointXY(x, y));
if (QgsWkbTypes::hasM(layerWKBType))
{
	Geo.get()->addMValue();
}
if (QgsWkbTypes::hasZ(layerWKBType))
{
	Geo.get()->addZValue();
}

//线
QgsGeometry Geo = QgsGeometry::fromPolyline(poly);
if (QgsWkbTypes::hasM(layerWKBType))
{
	Geo.get()->addMValue();
}
if (QgsWkbTypes::hasZ(layerWKBType))
{
	Geo.get()->addZValue();
}
//面
QgsGeometry Geo = QgsGeometry::fromPolyline(poly);
QVector<QgsGeometry> vGeo;
vGeo.append(Geo);
QgsGeometry polygonGeo = Geo.polygonize(vGeo);
if (QgsWkbTypes::hasM(layerWKBType))
{
	polygonGeo.get()->addMValue();
}
if (QgsWkbTypes::hasZ(layerWKBType))
{
	polygonGeo.get()->addZValue();
}

4、添加到图层

QgsFeature  Feature = QgsVectorLayerUtils::
	createFeature(currentLayer,Geo或者polygonGeo, 属性键值对集合(QgsAttributeMap类型,选填));
currentLayer->addFeature(Feature);	
currentLayer->commitChanges();

5、设置画布缩放 刷新画布

QgsRectangle boundingBox = Geo.boundingBox();
boundingBox.grow(10);
MainWindow::TheInstance()->getActiveMapCanvas()->setExtent(boundingBox);
MainWindow::TheInstance()->getActiveMapCanvas()->refresh();

关于如何声明一个属性键值对集合

//获取当前图层的属性项(字段) 返回的是一个属性项集合
QgsFields fields = currentLayer->fields();
//声明一个map集合,可以多次插入键值对
QgsAttributeMap map;
map.insert(fields.indexOf(属性项的name), QVariant(属性值));

关于如何写入属性项(字段)

QList<QgsField> fieldList;
	QgsFields currentLayerFields = currentLayer->fields();
	QStringList fields = {你要插入的字段 };

	for (int i = 0; i < fields.count(); ++i)
	{
		//如果该不存在,则插入
		if (currentLayerFields.indexFromName(fields.at(i)) == -1)
		{
			QgsField shpField(fields.at(i), QVariant::String);
			fieldList.push_back(shpField);
		}
	}
	QgsVectorDataProvider* vectorProvider = currentLayer->dataProvider();
	vectorProvider->addAttributes(fieldList);
	currentLayer->updateFields();