来自 Qt 中 main.cpp 代码的 MainWindow

Question

想了解 MainWindow 和 main.cpp 之间的代码差异。具体来说，如何将 main.cpp 中专门编写的一段代码修改为 mainwindow.cpp 和 mainwindow.h 的一部分。

举个例子，我正在尝试修改中的代码以在 MainWindow 中工作。

main.cpp

#include <QtWidgets>
#include <QtNetwork>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    //setup GUI (you could be doing this in the designer)
    QWidget widget;
    QFormLayout layout(&widget);
    QLineEdit lineEditName;
    QLineEdit lineEditGender;
    QLineEdit lineEditRegion;
    auto edits = {&lineEditName, &lineEditGender, &lineEditRegion};
    for(auto edit : edits) edit->setReadOnly(true);
    layout.addRow("Name:", &lineEditName);
    layout.addRow("Gender:", &lineEditGender);
    layout.addRow("Region:", &lineEditRegion);
    QPushButton button("Get Name");
    layout.addRow(&button);

    //send request to uinames API
    QNetworkAccessManager networkManager;
    QObject::connect(&networkManager, &QNetworkAccessManager::finished,
                 [&](QNetworkReply* reply){
        //this lambda is called when the reply is received
        //it can be a slot in your GUI window class
        //check for errors
        if(reply->error() != QNetworkReply::NoError){
            for(auto edit : edits) edit->setText("Error");
            networkManager.clearAccessCache();
        } else {
            //parse the reply JSON and display result in the UI
            QJsonObject jsonObject=     QJsonDocument::fromJson(reply->readAll()).object();
            QString fullName= jsonObject["name"].toString();
            fullName.append(" ");
            fullName.append(jsonObject["surname"].toString());
            lineEditName.setText(fullName);
            lineEditGender.setText(jsonObject["gender"].toString());
            lineEditRegion.setText(jsonObject["region"].toString());
        }
        button.setEnabled(true);
        reply->deleteLater();
        });
     //url parameters
    QUrlQuery query;
    query.addQueryItem("amount", "1");
    query.addQueryItem("region", "United States");
    QUrl url("http://uinames.com/api/");
    url.setQuery(query);
    QNetworkRequest networkRequest(url);
    //send GET request when the button is clicked
    QObject::connect(&button, &QPushButton::clicked, [&](){
        networkManager.get(networkRequest);
        button.setEnabled(false);
        for(auto edit : edits) edit->setText("Loading. . .");
    });

    widget.show();
    return a.exec();
}

编辑

添加了相同答案的计时器部分；请演示这个带有计时器的版本如何完成

QTimer timer;
QObject::connect(&timer, &QTimer::timeout, [&](){
    networkManager.get(networkRequest);
    button.setEnabled(false);
    for(auto edit : edits) edit->setText("Loading. . .");
});
timer.start(60000); //60000 msecs = 60 secs

我努力将 networkManager 修改为 class 成员，如何构建代码以及如何替换 lambda 函数。

如果有人可以提供所有需要的修改，让我更好地理解，那就太好了。

Answer 1

您可以将所有这些代码放入 QMainWindow 的构造函数中，并按原样保留 lambda 函数。

另一种更简洁的方法是将这些 lambda 函数转换为专用槽。使用这种方式，您应该将 networkManager 定义为 QMainWindow class 的 class 成员，并且它应该分配在堆内存中而不是堆栈中。要完成此操作，只需定义一个 QNetworkManager* class 成员并在 QMainWindow 构造函数中对其进行初始化。

this->networkManager = new QNetworkManager(this);

初始化后，您可以在 QMainWindow class.

的所有插槽中使用它

一个简单的经验法则是：lambda 函数和主作用域之间的所有共享变量都应该是 class 成员这样。

代码。（我测试了它并且工作正常）

main.cpp

#include "mainwindow.h"
#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();

    return a.exec();
}

mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    ui->lineEditGender->setReadOnly(true);
    ui->lineEditRegion->setReadOnly(true);
    ui->lineEditName->setReadOnly(true);

    networkManager = new QNetworkAccessManager(this);

    connect(networkManager, &QNetworkAccessManager::finished, this, &MainWindow::onNetworkManagerFinished);
    connect(ui->btnGetName, &QPushButton::clicked, this, &MainWindow::onBtnGetNameClicked);
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::onNetworkManagerFinished(QNetworkReply *reply)
{
    if(reply->error() != QNetworkReply::NoError){
        ui->lineEditName->setText("Error");
        ui->lineEditGender->setText("Error");
        ui->lineEditRegion->setText("Error");

        networkManager->clearAccessCache();
    } else {
        //parse the reply JSON and display result in the UI
        QJsonObject jsonObject = QJsonDocument::fromJson(reply->readAll()).object();
        QString fullName= jsonObject["name"].toString();
        fullName.append(" ");
        fullName.append(jsonObject["surname"].toString());
        ui->lineEditName->setText(fullName);
        ui->lineEditGender->setText(jsonObject["gender"].toString());
        ui->lineEditRegion->setText(jsonObject["region"].toString());
    }
    ui->btnGetName->setEnabled(true);
    reply->deleteLater();
}

void MainWindow::onBtnGetNameClicked()
{
    QUrlQuery query;
    query.addQueryItem("amount", "1");
    query.addQueryItem("region", "United States");
    QUrl url("http://uinames.com/api/");
    url.setQuery(query);
    QNetworkRequest networkRequest(url);

    //send GET request when the button is clicked
    networkManager->get(networkRequest);
    ui->btnGetName->setEnabled(false);

    ui->lineEditName->setText("Loading. . .");
    ui->lineEditGender->setText("Loading. . .");
    ui->lineEditRegion->setText("Loading. . .");
}

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QNetworkAccessManager>
#include <QNetworkReply>
#include <QNetworkRequest>
#include <QUrlQuery>
#include <QJsonDocument>
#include <QJsonObject>

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

private slots:
    void onNetworkManagerFinished(QNetworkReply* reply);
    void onBtnGetNameClicked();

private:
    Ui::MainWindow *ui;
    QNetworkAccessManager *networkManager;
};

#endif // MAINWINDOW_H

Answer 2

您可能希望将用户界面和控制器（业务逻辑）分离成单独的 classes。

main() 的主体实例化 ui 和控制器并连接它们。每 5 秒获取新结果的计时器。计时器也可以滚动到 Controller 中 - 我展示它作为一个例子将它分开作为向现有 class 添加功能而不修改它的示例。

main.cpp

// https://github.com/KubaO/Whosebugn/tree/master/questions/into-mainwin-39643510
#include "mainwindow.h"
#include "controller.h"

int main(int argc, char *argv[])
{
   QApplication app{argc, argv};
   MainWindow ui;
   Controller ctl;
   QTimer timer;
   timer.start(5*1000);
   QObject::connect(&timer, &QTimer::timeout, &ctl, &Controller::get);

   QObject::connect(&ctl, &Controller::busy, &ui, [&]{ ui.setState(MainWindow::Loading); });
   QObject::connect(&ui, &MainWindow::request, &ctl, &Controller::get);
   QObject::connect(&ctl, &Controller::error, &ui, [&]{ ui.setState(MainWindow::Error); });
   QObject::connect(&ctl, &Controller::values, &ui, &MainWindow::setFields);
   ui.show();
   return app.exec();
}

控制器对用户界面一无所知，只负责处理请求。每次开始处理请求时，它都会发出 busy 信号。

如果你想为多个活动请求提供更好的反馈，busy 信号只需要在没有待处理的请求并添加新请求时发出，并且 idle当最后一个请求完成并且没有更多待处理的请求时，将发出信号。

controller.h

#ifndef CONTROLLER_H
#define CONTROLLER_H

#include <QtNetwork>

class Controller : public QObject {
   Q_OBJECT
   QNetworkAccessManager manager{this};
   QNetworkRequest request;
   Q_SLOT void onReply(QNetworkReply *);
public:
   explicit Controller(QObject * parent = nullptr);
   Q_SLOT void get();
   Q_SIGNAL void busy();
   Q_SIGNAL void error(const QString &);
   Q_SIGNAL void values(const QString & name, const QString & gender, const QString & region);
};

#endif // CONTROLLER_H

controller.cpp

#include "controller.h"

Controller::Controller(QObject *parent) : QObject(parent)
{
   QUrlQuery query;
   query.addQueryItem("amount", "1");
   query.addQueryItem("region", "United States");
   QUrl url("http://uinames.com/api/");
   url.setQuery(query);
   request = QNetworkRequest(url);
   connect(&manager, &QNetworkAccessManager::finished, this, &Controller::onReply);
}

void Controller::onReply(QNetworkReply * reply) {
   if (reply->error() != QNetworkReply::NoError) {
      emit error(reply->errorString());
      manager.clearAccessCache();
   } else {
      //parse the reply JSON and display result in the UI
      auto jsonObject = QJsonDocument::fromJson(reply->readAll()).object();
      auto fullName = jsonObject["name"].toString();
      fullName.append(" ");
      fullName.append(jsonObject["surname"].toString());
      emit values(fullName, jsonObject["gender"].toString(), jsonObject["region"].toString());
   }
   reply->deleteLater();
}

void Controller::get() {
   emit busy();
   manager.get(request);
}

用户界面对任何业务逻辑一无所知，它提供了一个足以让业务逻辑使用它的API。它可以处于三种状态之一：Normal 结果可见的状态，Loading 显示忙碌反馈的状态，以及显示错误信息的 Error 状态。 setFields槽returns状态为Normal.

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QtWidgets>

class MainWindow : public QWidget {
  Q_OBJECT
  QFormLayout layout{this};
  QLineEdit lineEditName;
  QLineEdit lineEditGender;
  QLineEdit lineEditRegion;
  QPushButton button{"Get Name"};
  QLineEdit * edits[3] = {&lineEditName, &lineEditGender, &lineEditRegion};
public:
  enum State { Normal, Loading, Error };
  explicit MainWindow(QWidget * parent = nullptr);
  Q_SLOT void setFields(const QString & name, const QString & gender, const QString & region);
  Q_SLOT void setState(State);
  Q_SIGNAL void request();
};

#endif // MAINWINDOW_H

mainwindow.cpp

#include "mainwindow.h"

MainWindow::MainWindow(QWidget *parent) : QWidget(parent)
{
   for(auto edit : edits) edit->setReadOnly(true);
   layout.addRow("Name:", &lineEditName);
   layout.addRow("Gender:", &lineEditGender);
   layout.addRow("Region:", &lineEditRegion);
   layout.addRow(&button);
   connect(&button, &QPushButton::clicked, this, &MainWindow::request);
}

void MainWindow::setFields(const QString & name, const QString & gender, const QString & region) {
   setState(Normal);
   lineEditName.setText(name);
   lineEditGender.setText(gender);
   lineEditRegion.setText(region);
}

void MainWindow::setState(MainWindow::State state) {
   if (state == Normal) {
      for (auto edit : edits) edit->setEnabled(true);
      button.setEnabled(true);
   }
   else if (state == Loading) {
      for (auto edit : edits) edit->setEnabled(false);
      button.setEnabled(false);
   }
   else if (state == Error) {
      for (auto edit : edits) edit->setText("Error...");
      button.setEnabled(true);
   }
}

来自 Qt 中 main.cpp 代码的 MainWindow

MainWindow from code from the main.cpp in Qt

qt

qt-creator

qmainwindow

main.cpp

controller.h

controller.cpp

mainwindow.h

mainwindow.cpp