全网最新QGIS3.16插件开发

以图层叠加分析计算相交面积

环境准备

之前分享过基于QGIS3.4的开发，这里将环境升级为QGIS3.16.14 LTR(长期维护版)

更详细的配置可以参考我上一篇文章

官网地址 (opens new window)

升级很简单，直接卸载之前的3.4版本，然后将3.16.14版本安装即可

操作基本一致没什么改变，QC可以继续使用，不用换

插件的位置还是在原来的位置不用更换(每个人的用户名可能不一样，我这里是Administartor)

C:\Users\Administrator\AppData\Roaming\QGIS\QGIS3\profiles\default\python\plugins

修改pycharm的python环境配置

1. 打开设置

2. 打开python环境设置

3. 选择QGIS自带的开发环境

选择python-qgis-ltr.bat

可以看到QGIS3.16的python版本为3.9，并且已经包含所需要的环境，最新的版本在后面也有提示

插件开发

目标

我们在开发插件的时候，必须要明确自己开发插件的用途，如果我们需要的功能已经有插件了就不要再开发了，避免重复造轮子

图层叠加分析计算相交面积

我的业务逻辑

1. 使用条件筛选出图层中需要的数据
2. 与业务图层相交
3. 将相交的结果以业务图层的id分组融合
4. 使用字段计算器计算融合后数据的面积生成新的字段存储结果
5. 将融合后的数据关联到原来的业务图层中并保留新的结果字段

开发

项目还是使用之前的geotest进行开发

QC设计界面

新的界面设计和组件命名如下：

核型代码

这里修改geotest.py文件，核心的计算代码都在这

修改内容如下：

# -*- coding: utf-8 -*-
"""
/***************************************************************************
 geotest
                                 A QGIS plugin
 测试工具
 Generated by Plugin Builder: http://g-sherman.github.io/Qgis-Plugin-Builder/
                              -------------------
        begin                : 2021-12-13
        git sha              : $Format:%H$
        copyright            : (C) 2021 by sunbt
        email                : 1327398885@qq.com
 ***************************************************************************/

/***************************************************************************
 *                                                                         *
 *   This program is free software; you can redistribute it and/or modify  *
 *   it under the terms of the GNU General Public License as published by  *
 *   the Free Software Foundation; either version 2 of the License, or     *
 *   (at your option) any later version.                                   *
 *                                                                         *
 ***************************************************************************/
"""
import processing
from qgis.PyQt.QtCore import QSettings, QTranslator, QCoreApplication
from qgis.PyQt.QtGui import QIcon
from qgis.PyQt.QtWidgets import QAction, QFileDialog, QProgressBar
from qgis.core import *

# Initialize Qt resources from file resources.py


from .resources import *
# Import the code for the dialog
from .geotest_dialog import geotestDialog
import os.path


class geotest:
    """QGIS Plugin Implementation."""

    def __init__(self, iface):
        """Constructor.

        :param iface: An interface instance that will be passed to this class
            which provides the hook by which you can manipulate the QGIS
            application at run time.
        :type iface: QgsInterface
        """
        # Save reference to the QGIS interface
        self.iface = iface
        # initialize plugin directory
        self.plugin_dir = os.path.dirname(__file__)
        # initialize locale
        locale = QSettings().value('locale/userLocale')[0:2]
        locale_path = os.path.join(
            self.plugin_dir,
            'i18n',
            'geotest_{}.qm'.format(locale))

        if os.path.exists(locale_path):
            self.translator = QTranslator()
            self.translator.load(locale_path)
            QCoreApplication.installTranslator(self.translator)

        # Declare instance attributes
        self.actions = []
        self.menu = self.tr(u'&geotest')

        # Check if plugin was started the first time in current QGIS session
        # Must be set in initGui() to survive plugin reloads
        self.first_start = None

    # noinspection PyMethodMayBeStatic
    def tr(self, message):
        """Get the translation for a string using Qt translation API.

        We implement this ourselves since we do not inherit QObject.

        :param message: String for translation.
        :type message: str, QString

        :returns: Translated version of message.
        :rtype: QString
        """
        # noinspection PyTypeChecker,PyArgumentList,PyCallByClass
        return QCoreApplication.translate('geotest', message)

    def add_action(
            self,
            icon_path,
            text,
            callback,
            enabled_flag=True,
            add_to_menu=True,
            add_to_toolbar=True,
            status_tip=None,
            whats_this=None,
            parent=None):
        """Add a toolbar icon to the toolbar.

        :param icon_path: Path to the icon for this action. Can be a resource
            path (e.g. ':/plugins/foo/bar.png') or a normal file system path.
        :type icon_path: str

        :param text: Text that should be shown in menu items for this action.
        :type text: str

        :param callback: Function to be called when the action is triggered.
        :type callback: function

        :param enabled_flag: A flag indicating if the action should be enabled
            by default. Defaults to True.
        :type enabled_flag: bool

        :param add_to_menu: Flag indicating whether the action should also
            be added to the menu. Defaults to True.
        :type add_to_menu: bool

        :param add_to_toolbar: Flag indicating whether the action should also
            be added to the toolbar. Defaults to True.
        :type add_to_toolbar: bool

        :param status_tip: Optional text to show in a popup when mouse pointer
            hovers over the action.
        :type status_tip: str

        :param parent: Parent widget for the new action. Defaults None.
        :type parent: QWidget

        :param whats_this: Optional text to show in the status bar when the
            mouse pointer hovers over the action.

        :returns: The action that was created. Note that the action is also
            added to self.actions list.
        :rtype: QAction
        """

        icon = QIcon(icon_path)
        action = QAction(icon, text, parent)
        action.triggered.connect(callback)
        action.setEnabled(enabled_flag)

        if status_tip is not None:
            action.setStatusTip(status_tip)

        if whats_this is not None:
            action.setWhatsThis(whats_this)

        if add_to_toolbar:
            # Adds plugin icon to Plugins toolbar
            self.iface.addToolBarIcon(action)

        if add_to_menu:
            self.iface.addPluginToMenu(
                self.menu,
                action)

        self.actions.append(action)

        return action

    def initGui(self):
        """Create the menu entries and toolbar icons inside the QGIS GUI."""

        icon_path = ':/plugins/geotest/icon.png'
        self.add_action(
            icon_path,
            text=self.tr(u'geotest'),
            callback=self.run,
            parent=self.iface.mainWindow())

        # will be set False in run()
        self.first_start = True

    def unload(self):
        """Removes the plugin menu item and icon from QGIS GUI."""
        for action in self.actions:
            self.iface.removePluginMenu(
                self.tr(u'&geotest'),
                action)
            self.iface.removeToolBarIcon(action)

    # 加载二调文件的路径
    def select_shperdiao_file(self):
        filename, _filter = QFileDialog.getOpenFileName(
            self.dlg, "Select input file", "", "*.shp"
        )
        self.dlg.lineEditShperdiao.setText(filename)

    # 加载业务文件的路径
    def select_shpyewu_file(self):
        filename, _filter = QFileDialog.getOpenFileName(
            self.dlg, "Select input file", "", "*.shp"
        )
        self.dlg.lineEditShpyewu.setText(filename)

    # 导出shp文件的路径
    def select_output_file(self):
        filename, _filter = QFileDialog.getSaveFileName(
            self.dlg, "Select output file", "", "*.shp"
        )
        self.dlg.lineEditShpOut.setText(filename)

    # 执行计算
    def filter(self, input_path, yewu_path, output_path, layerName):
        outputs = {}
        tempPath = "D:\data\gis\output"

        # 按表达式提取
        alg_params = {
            'EXPRESSION': '\"DLBM\"=201 or \"DLBM\"=202 or \"DLBM\"=203 or \"DLBM\"=204 or \"DLBM\"=205 or \"DLBM\"=101 or \"DLBM\"=102 or \"DLBM\"=105 or \"DLBM\"=106 or \"DLBM\"=113 or \"DLBM\"=118',
            'INPUT': input_path,
            'OUTPUT': QgsProcessing.TEMPORARY_OUTPUT
        }
        outputs[''] = processing.run('native:extractbyexpression', alg_params)

        # 相交
        alg_params = {
            'INPUT': outputs['']['OUTPUT'],
            'INPUT_FIELDS': [''],
            'OVERLAY': yewu_path,
            'OVERLAY_FIELDS': [''],
            'OVERLAY_FIELDS_PREFIX': '',
            'OUTPUT': QgsProcessing.TEMPORARY_OUTPUT
        }
        outputs[''] = processing.run('native:intersection', alg_params)

        # 融合
        alg_params = {
            'FIELD': ['JCBH'],
            'INPUT': outputs['']['OUTPUT'],
            'OUTPUT': QgsProcessing.TEMPORARY_OUTPUT
        }
        outputs[''] = processing.run('native:dissolve', alg_params)

        # 字段计算器
        alg_params = {
            'FIELD_LENGTH': 10,
            'FIELD_NAME': '建设用地1',
            'FIELD_PRECISION': 2,
            'FIELD_TYPE': 0,
            'FORMULA': ' round(($area * 0.0015),2)',
            'INPUT': outputs['']['OUTPUT'],
            'OUTPUT': 'TEMPORARY_OUTPUT',
            'OUTPUT': QgsProcessing.TEMPORARY_OUTPUT
        }
        outputs[''] = processing.run('native:fieldcalculator', alg_params)

        # 按字段值连接属性
        alg_params = {
            'DISCARD_NONMATCHING': False,
            'FIELD': 'JCBH',
            'FIELDS_TO_COPY': ['建设用地1'],
            'FIELD_2': 'JCBH',
            'INPUT': yewu_path,
            'INPUT_2': outputs['']['OUTPUT'],
            'METHOD': 1,
            'PREFIX': '',
            'OUTPUT': output_path
        }
        outputs[''] = processing.run('native:joinattributestable',alg_params)

    def run(self):
        """Run method that performs all the real work"""

        # Create the dialog with elements (after translation) and keep reference
        # Only create GUI ONCE in callback, so that it will only load when the plugin is started
        if self.first_start == True:
            self.first_start = False
            self.dlg = geotestDialog()
            # 点击按钮，确定路径
            self.dlg.pushButtonShperdiao.clicked.connect(self.select_shperdiao_file)
            self.dlg.pushButtonShpyewu.clicked.connect(self.select_shpyewu_file)
            self.dlg.pushButtonShpOut.clicked.connect(self.select_output_file)
        # show the dialog
        self.dlg.show()
        # Run the dialog event loop
        result = self.dlg.exec_()
        # See if OK was pressed
        if result:
            # Do something useful here - delete the line containing pass and
            # substitute with your code.
            # 获取二调文件路径
            shperdiaoPath = self.dlg.lineEditShperdiao.text()
            # 业务图斑文件位置
            shpyewu = self.dlg.lineEditShpyewu.text()
            # 获取导出结果文件路径
            outPath = self.dlg.lineEditShpOut.text()

            # 图层名称
            layerName = outPath.split("/")[len(outPath.split("/")) - 1].replace(".shp", "")
            # 执行方法
            self.filter(shperdiaoPath, shpyewu, outPath, layerName)
            # 将结果添加到窗口中
            vlayer = QgsVectorLayer(outPath, layerName, "ogr")
            if vlayer.isValid():
                QgsProject.instance().addMapLayer(vlayer)
            else:
                print("图层加载失败！")

            pass
            # 在QGIS界面上打印结果
            self.iface.messageBar().pushMessage("成功", "加载图层：" + layerName, level=Qgis.Success)

这里有几点要说明一下：

1. 在QGIS的插件开发中需要使用系统工具时需要引入processing

import processing

使用时如下：以按表达式筛选为例

        # 按表达式提取
        alg_params = {
            'EXPRESSION': '\"DLBM\"=201 or \"DLBM\"=202 or \"DLBM\"=203 or \"DLBM\"=204 or \"DLBM\"=205 or \"DLBM\"=101 or \"DLBM\"=102 or \"DLBM\"=105 or \"DLBM\"=106 or \"DLBM\"=113 or \"DLBM\"=118',
            'INPUT': input_path,
            'OUTPUT': QgsProcessing.TEMPORARY_OUTPUT
        }
        outputs[''] = processing.run('native:extractbyexpression', alg_params)

2. 其中 QgsProcessing.TEMPORARY_OUTPUT，这里表示使用临时存储，不会保存到磁盘中

3. 在使用pycharm可能会提示找不到引入的方法，这里可以不用管

结果

我的代码就在QGIS的插件文件夹下：

修改代码后只需要reload一下即可

成果如下：

执行后的结果如下：

打开属性表后可以看到计算完成的结果