QProgressDialog使用时不显示的可能问题 #Qt #C++

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QProgressDialong是Qt提供的用于显示各类耗时较长的操作进度，

而不至于让程序看上去假死了一样，他继承自QDialog。

example：http://doc.qt.io/qt-4.8/qprogressdialog.html#labelText-prop

但是在测试中会出现Dialog不显示，程序依旧进入假死状态，在网上也查阅不到问题所在。

不显示的原因是QProgressDialog有一个智能延迟，默认一切短于4秒的操作都不显示Dialog，因为测试时的数据量往往很小，从而导致了问题。

文档是这么说的：

A common problem with progress dialogs is that it is difficult to know when to use them; operations take different amounts of time on different hardware.QProgressDialog offers a solution to this problem: it estimates the time the operation will take (based on time for steps), and only shows itself if that estimate is beyondminimumDuration() (4 seconds by default).

所以只要使用

void setMinimumDuration(int ms)

将这个值改小或者为0，就可以了。下面是代码：

void MainWindow::sendAll(){    int count = 0;    for(unsigned int i=0;i<ARRAY.size();i++)    {        count+=ARRAY.at(i).size();    }    int num = 0;    QProgressDialog progress_dialog("Sending values to Units...","Cancel",0,count,this);    progress_dialog.setWindowModality(Qt::WindowModal);    progress_dialog.setMinimumDuration(0);    progress_dialog.setWindowFlags(Qt::Dialog | Qt::CustomizeWindowHint | Qt::WindowTitleHint);    progress_dialog.setFixedSize(500,120);    progress_dialog.setWindowTitle("Sending values to Units...");    for(unsigned int m = 0; m<ARRAY.size();m++)    {        int i = 0;        QString ip = "";        QString port = "";        QString unit_id = "";        while(ui->activeUnitWidget->item(m)->text()[i]!=':')        {            ip.append(ui->activeUnitWidget->item(m)->text()[i]);            i++;        }        i++;        while(ui->activeUnitWidget->item(m)->text()[i]!='[')        {            port.append(ui->activeUnitWidget->item(m)->text()[i]);            i++;        }        i++;        while(ui->activeUnitWidget->item(m)->text()[i]!=']')        {            unit_id.append(ui->activeUnitWidget->item(m)->text()[i]);            i++;        }        vector<addr_value>::iterator innerIter;        for(innerIter=ARRAY.at(m).begin(); innerIter!=ARRAY.at(m).end() ; innerIter++)        {            progress_dialog.setLabelText("Sending values to.."+ui->activeUnitWidget->item(m)->text());            M_Client A(ip.toLatin1(),port.toInt(),unit_id.toInt());            A.Connect();            A.Modbus_sender_single(num, innerIter->addr , innerIter->value);            A.Close();            progress_dialog.setValue(++num);            //Sleep(40);        }    }}

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