通过 Signal/Slot 机制将 QString 传递给 QThread

Question

我无法让我的 MainWindow 与 Worker 线程通信。我正在使用通常的 SIGNAL/SLOT 机制传递 QString 对象。我的程序应该将 QString "Alice" 从 MainWindow 传输到在 QThread 中处理的类 Worker 的工作对象，然后再返回。代码编译没有错误，并且在我的 MacBook Pro 上使用 Qt 4.8 和 Clang 运行顺利。这是显示我的问题的最少代码。

ma​​inwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <worker.h>

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

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

private:
    Ui::MainWindow *ui;
    QString name;
private slots:
    void errorString(QString);

public slots:
    void getFromWorker(QString);

signals:
    void sendToWorker(QString);
};

#endif // MAINWINDOW_H

ma​​inwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QThread>
#include <QDebug>

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

    name = "Alice";
    qDebug() << "The name in MainWindow is: " << name << " from ThreadID = " << QThread::currentThreadId();
    ThreadedWork();
    qDebug() << "Name sent from the Worker Thread is: " << name;
}

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

void MainWindow::errorString(QString string)
{
    qDebug() << "The error from the threaded process is: " << string;
}

void MainWindow::ThreadedWork()
{
    Worker* worker = new Worker;
    emit sendToWorker(name);
    connect(this,SIGNAL(sendToWorker(QString)),worker,SLOT(getFromMain(QString)));
    connect(worker,SIGNAL(sendToMain(QString)),this,SLOT(getFromWorker(QString)));

    QThread *thread = new QThread;
    worker->moveToThread(thread);

    connect(worker, SIGNAL(error(QString)), this, SLOT(errorString(QString)));
    connect(thread, SIGNAL(started()), worker, SLOT(process()));
    connect(worker, SIGNAL(finished()), thread, SLOT(quit()));
    connect(worker, SIGNAL(finished()), worker, SLOT(deleteLater()));
    connect(thread, SIGNAL(finished()), thread, SLOT(deleteLater()));

    thread->start();
}

void MainWindow::getFromWorker(QString someName) //slot implementation
{
    name = someName;
}

worker.h

#ifndef WORKER_H
#define WORKER_H

#include <QObject>

class Worker : public QObject
{
    Q_OBJECT
public:
    explicit Worker(Worker * parent = 0);
    ~Worker();

signals:
    void sendToMain(QString);
    void error(QString err);
    void finished();

public slots:
    void getFromMain(QString);
    void process();

private:
    QString name;
};

#endif // WORKER_H

worker.cpp

#include "worker.h"
#include <QDebug>
#include <QThread>

Worker::Worker(Worker * parent)
{

}

Worker::~Worker()
{

}

void Worker::process() {
    // allocate resources using new here
    qDebug() << "name recieved from Main is: " << name;
    qDebug() << "name passed to Worker Thread is: " << name << " having ThreadID = " << QThread::currentThreadId();
    emit sendToMain(name);
    emit finished();
}

void Worker::getFromMain(QString someName) // slot implementation
{
    name = someName;
}

我的输出是：

The name in MainWindow is:  "Alice"  from ThreadID =  0x7fff7de7a300 
Name sent from the Worker Thread is:  "Alice" 
name recieved from Main is:  "" 
name passed to Worker Thread is:  ""  having ThreadID =  0x1107a9000

如上所述，我无法将 QString "Alice" 传递给工作人员。我在这里错过了什么？

Answer 1

ThreadedWork() 方法的问题：

您首先发出信号emit sendToWorker(name);，然后只有他们将这个信号连接到插槽-这是您失败的根源。

像这样换行：

void MainWindow::ThreadedWork()
{
    Worker* worker = new Worker;

    connect(this,SIGNAL(sendToWorker(QString)),worker,SLOT(getFromMain(QString)));
    connect(worker,SIGNAL(sendToMain(QString)),this,SLOT(getFromWorker(QString)));

    emit sendToWorker(name);

    QThread *thread = new QThread;
    worker->moveToThread(thread);
...
}

我可能会得到预期的结果：

The name in MainWindow is:  "Alice"  from ThreadID =  0xcbc
Name sent from the Worker Thread is:  "Alice"
name recieved from Main is:  "Alice"
name passed to Worker Thread is:  "Alice"  having ThreadID =  0xff8