pyqgis学习

1.
错误：ImportError: No module named qgis.core
解决方法：python的qgis,初始化变量:
D:\PROGRA~1\QGIS3~1.0\OSGeo4W.bat
D:\PROGRA~1\QGIS3~1.0\bin\py3_env.bat
D:\PROGRA~1\QGIS3~1.0\bin\qt5_env.bat
SET PYTHONPATH=D:\PROGRA~1\QGIS3~1.0\apps\qgis\python;D:\PROGRA~1\QGIS3~1.0\apps\Qt5\plugins
SET PATH=D:\PROGRA~1\QGIS3~1.0\apps\Qt5\plugins;%PATH%

2.
错误：This application failed to start because it could not find or load the Qt platform plugin "windows"
in "".
解决方法：把 包含qwindows.dll的目录platform复制到 D:\Program Files\QGIS 3.0\bin

3.
错误：QgisProject.read和QgisVectorLayer构造失败
解决方法：
环境变量没有设定好，在qgis.bat基础上去掉启动qgis,增加环境变量PYTHONPATH

4.
错误：QtCore.pyqtSignal信号发射接收问题解决
解决方法：
1.QtCore.pyqtSignal必须声明为类的变量
2.所在类必须继承与QtObject
3.构造函数必须直接调用QtCore.QObject.__init__(self)

5.
错误：在qtthread中启动httpserver崩溃的问题
解决方法：
1.原因python的httpserver模块默认打印到控制台，会导致qgis应为同步问题崩溃
2.重载BaseHTTPRequestHandler的log_message方法，去掉打印

5.
多线程使用HTTPServer服务，并和主线程通讯的例子

from http.server import BaseHTTPRequestHandler
from http.server import HTTPServer
from PyQt5 import QtCore
import time

class MyHttpServer(HTTPServer):
    def log_message(self, format, *args):
        pass

class TodoHandler(BaseHTTPRequestHandler):
    def do_GET(self):
        if self.path != '/':
            self.send_error(404, "File not found.")
            return
        self.send_response(200)
        self.send_header('Content-type', 'application/json')
        self.end_headers()
        self.wfile.write(b"{}")

        self.server.request_.emit( 5.0, 5.0 )
 
    def log_message(self, format, *args):
        pass

class TestRun(QtCore.QObject):

    request_ = QtCore.pyqtSignal(float, float)

    def __init__(self):
        QtCore.QObject.__init__(self)

    def run(self):
        #for i in range(0,100):
        #    time.sleep(0.1)
        #    print(i)
        #print('-- server running --')
        server = MyHttpServer(('localhost', 8888), TodoHandler)
        server.request_ = self.request_
        server.serve_forever()

class TestRev(QtCore.QObject):
    def __init__(self):
        QtCore.QObject.__init__(self)

    def onRequest(self, x, y):
        ext = iface.mapCanvas().extent()
        ext += QgsVector(int(x),int(y))
        iface.mapCanvas().setExtent(ext)

    def onError(self, e, exception_string):
        print('Worker thread raised an exception:\n'.format(exception_string))
    
a = TestRev()

r = TestRun()
t = QtCore.QThread()
r.moveToThread(t)
r.request_.connect(a.onRequest)
t.started.connect(r.run)
t.start()