Qt子線程如何更新UI？

和其他語言類似，不能直接在子線程更新UI，可以通過signal－slot機制在UI線程進行更新。

Signal-slot機制可以在不同對象，不同線程之間進行通訊。

例子：

<pre name="code" class="cpp">//main.cpp
#include "mainwindow.h"
#include <QApplication>

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

    return a.exec();
}

</pre><pre name="code" class="cpp">

</pre><pre name="code" class="cpp">

</pre><pre name="code" class="cpp">//mythread.h

#include <QThread>
#include <QTextEdit>

class MyThread : public QThread
{
    Q_OBJECT
public:
    explicit MyThread(QObject *parent = 0);
    virtual void run();

signals:
    void dataChanged(QString);

public slots:

};

//mythread.cpp
#include "mythread.h"
#include <QDebug>

MyThread::MyThread(QObject *parent) :
    QThread(parent)
{
}

void MyThread::run()
{
    long long int i;
    for(i = 10000000000; i > 0; i--)
    {
        qDebug() << "now i is: " << i;
        QThread::msleep(100);
        /*can not operate the GUI directly from another thread, I guess signal-slot mechanism should be used.
        //this->tEdit->setText("test");
        */
        QString str = QString::number(i);
        emit dataChanged("now i is: " + str);
    }
}

//mainwindow.h

//#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include "mythread.h"

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

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

private:
    Ui::MainWindow *ui;
    MyThread *t;

private slots:
    void longRunningTask();
    void testButtonClicked();


};



#endif // MAINWINDOW_H

//mainwindow.cpp
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QDebug>
#include "mythread.h"

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    t = new MyThread();
    connect(ui->pushButton,SIGNAL(clicked()),this, SLOT(longRunningTask()));
    connect(ui->pushButton_2,SIGNAL(clicked()),this,SLOT(testButtonClicked()));
    connect(t, SIGNAL(dataChanged(QString)), ui->textEdit, SLOT(append(QString)));
}

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


void MainWindow::longRunningTask()
{
    t->start();
}

void MainWindow::testButtonClicked()
{
    int i;
    for(i = 100; i > 0; i--)
    {
        qDebug() << "test button clicked for: " << i << "times";
    }
    ui->textEdit->setText("test button clicked");
}