112 获取快照数据

第四步，实现获取快照数据的功能。

112.1 实现功能

C:\Users\Minwei\Projects\Qt\Monitor\monitordialog.h：

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...
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#include <QLabel>
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...
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class MonitorDialog : public QDialog
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{
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    ...
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private slots:
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    ...
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    void on_m_snapshotReply_readyRead();
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    ...
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private:
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    ...
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    QNetworkReply* m_snapshotReply;
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    QByteArray m_snapshotData;
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    QLabel* m_labels[4];
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    int m_index;
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    ...
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};
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...

C:\Users\Minwei\Projects\Qt\Monitor\monitordialog.cpp：

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...
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MonitorDialog::MonitorDialog(QWidget *parent)
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    ...
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    , m_snapshotReply(Q_NULLPTR)
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    , m_index(0)
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    ...
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{
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    ...
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    m_labels[0] = ui->m_labSnapshot1;
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    m_labels[1] = ui->m_labSnapshot2;
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    m_labels[2] = ui->m_labSnapshot3;
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    m_labels[3] = ui->m_labSnapshot4;
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    ...
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}
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...
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void MonitorDialog::on_m_btnSnapshot_clicked()
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{
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    m_snapshotReply = m_access->get(QNetworkRequest(QUrl(
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        "http://192.168.0.111:8080?action=snapshot")));
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    connect(m_snapshotReply, SIGNAL(readyRead()),
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        this, SLOT(on_m_snapshotReply_readyRead()));
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}
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...
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void MonitorDialog::on_m_snapshotReply_readyRead()
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{
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    m_snapshotData += m_snapshotReply->readAll();
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    int begin = m_snapshotData.indexOf("\xff\xd8", 0);
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    if (begin == -1)
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    {
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        m_snapshotData.clear();
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        return;
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    }
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    int end = m_snapshotData.indexOf("\xff\xd9", begin + 2);
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    if (end == -1)
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        return;
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    QImage frame;
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    if (!frame.loadFromData(m_snapshotData.mid(begin, end + 2), "JPG"))
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    {
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        m_snapshotData.clear();
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        return;
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    }
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    m_snapshotData.clear();
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    m_labels[m_index]->setPixmap(QPixmap::fromImage(frame).scaledToHeight(236));
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    m_index = (m_index + 1) % 4;
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}
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...

112.2 测试验证

运行效果如图所示：