在Qt下呼叫外部指令

這裡透過Qt的QProcess來呼叫外部程式，並且把結果顯示在QTextEdit
main.cpp

#include <QApplication>
#include <QTextEdit>
#include <QProcess>

int main (
  int argc,
  char *argv[]
  )
{
  QApplication app (argc, argv);

  QTextEdit *TextEdit = new QTextEdit;

  TextEdit->show ();

  QProcess *proc = new QProcess;

//  proc->startDetached ("ping 168.95.1.1");
  proc->start ("ping 168.95.1.1");

  if (proc->waitForFinished (-1)) {
    TextEdit->append (proc->readAll ());
  } else {
    TextEdit->append ("Error");
  }

  return app.exec ();
}

不過，以上的程式有一個缺點，就是只有當外部指令結束之後，才會把結果顯示在QTextEdit裡面，這個時候會造成畫面當掉的感覺~

透過processEvent ()
可以適時的更新Qt的畫面~
但是仍會頓頓的~
main.cpp

#include <QApplication>
#include <QTextEdit>
#include <QProcess>

int main (
  int argc,
  char *argv[]
  )
{
  QApplication app (argc, argv);

  QTextEdit *TextEdit = new QTextEdit;

  TextEdit->show ();

  QProcess *proc = new QProcess (TextEdit);

  int x = 0;


//  proc->startDetached ("ping 168.95.1.1 -t");
  proc->start ("ping 168.95.1.1 -t");

  while (proc->state () == QProcess::Running) {
    x++;
//    while (1) {
    if (proc->waitForReadyRead (-1)) {
      if (x == 10) {
        proc->close ();
        break;
      }
      TextEdit->append (proc->readAll ());
      app.processEvents ();
    } else {
      TextEdit->append ("Error");
    }
  }

  return app.exec ();
}

最後，透過sign與slot，當有資料可讀的時候，才去讀資料，終於解決會頓頓的情況了。
以下是sample code
MyTextEdit.h

#ifndef _MY_TEXT_EDIT_H_
#define _MY_TEXT_EDIT_H_

#include <QTextEdit>

class QProcess;

class MyTextEdit : public QTextEdit {
  Q_OBJECT

  public:
    MyTextEdit (QWidget *parent = 0);
    void StartCmd ();

  public slots:
    void AppendContextFromStandOut ();
    void AppendContextFromStandErr ();
    void AppendContext ();

  private:
    QProcess *MyProc;
};

#endif //#ifndef _MY_TEXT_EDIT_H_

MyTextEdit.cpp

#include "MyTextEdit.h"
#include <QProcess>

MyTextEdit::MyTextEdit (QWidget *parent) : QTextEdit (parent) {
  // do nothing
}

void MyTextEdit::AppendContextFromStandOut () {
  this->append (MyProc->readAllStandardOutput ());
}

void MyTextEdit::AppendContextFromStandErr () {
  this->append (MyProc->readAllStandardError ());
}

void MyTextEdit::AppendContext () {
  this->append (MyProc->readAll ());
}

void MyTextEdit::StartCmd () {

  MyProc = new QProcess (this);

//  connect (MyProc, SIGNAL(readyReadStandardOutput ()), this, SLOT(AppendContextFromStandOut ()));
//  connect (MyProc, SIGNAL(readyReadStandardError ()), this, SLOT(AppendContextFromStandErr ()));
  connect (MyProc, SIGNAL(readyRead ()), this, SLOT(AppendContext ()));

  MyProc->start ("ping 168.95.1.1 -t");
}

main.cpp

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

int main (
  int argc,
  char *argv[]
  )
{
  QApplication app (argc, argv);

  MyTextEdit *TextEdit = new MyTextEdit;

  TextEdit->show ();

  TextEdit->StartCmd ();

  return app.exec ();
}

最後輸出如下

原版的如下：


耶，怎麼多出那麼多空白行呢?
為了去了解，輸出的內容是什麼，使用一個很好用的函式QByteArray::toHex ()
有以下三點發現
1. Qt還是使用Unix換行的方式，只有0x0a("\n")；而在Windows下的換行為0x0a("\r"),0x0d("\n")。因此，必需要移除掉多餘的0x0d
2. 我們由QProcess讀取出來的output本身就有換行符號(0x0a)，而每做一個QTextEdit::append ()前，也會跳到新的一行，因此，QTextEdit::append ()多的這一個換行就變成是多餘的了~所以，必需用QTextEdit::insertPlainText ()來取代
3. 因為，QTextEdit::insertPlainText ()是由目前鼠標的位置直接加入字串。所以必需另外，把QTextEdit設定為disable，避免讓使用著移動滑鼠來改變鼠標的位置。
只需要修改MyTextEdit.cpp，程式碼如下：

#include "MyTextEdit.h"
#include <QProcess>
#include <QChar>

MyTextEdit::MyTextEdit (QWidget *parent) : QTextEdit (parent) {
  this->setEnabled (false);
}

void MyTextEdit::AppendContextFromStandOut () {
  this->append (MyProc->readAllStandardOutput ());
}

void MyTextEdit::AppendContextFromStandErr () {
  this->append (MyProc->readAllStandardError ());
}

void MyTextEdit::AppendContext () {

  QByteArray TempByteArray(MyProc->readAll ());

  QString TempString(TempByteArray);

  TempString.remove (QChar(0x0d));

//  this->append (TempByteArray.toHex ());
//  this->append (TempString);
  this->insertPlainText (TempString);

}

void MyTextEdit::StartCmd () {

  MyProc = new QProcess (this);

//  connect (MyProc, SIGNAL(readyReadStandardOutput ()), this, SLOT(AppendContextFromStandOut ()));
//  connect (MyProc, SIGNAL(readyReadStandardError ()), this, SLOT(AppendContextFromStandErr ()));
  connect (MyProc, SIGNAL(readyRead ()), this, SLOT(AppendContext ()));

  MyProc->start ("ping 168.95.1.1");
}

結果如下：


但是，直接把0x0d("\r")這字元移除掉，看起來不是很好的辦法，理論上應該是把"\r\n"直接取代成"\n"比較合理
修改MyTextEdit.cpp結果如下：

#include "MyTextEdit.h"
#include <QProcess>
#include <QChar>

MyTextEdit::MyTextEdit (QWidget *parent) : QTextEdit (parent) {
  this->setEnabled (false);
}

void MyTextEdit::AppendContextFromStandOut () {
  this->append (MyProc->readAllStandardOutput ());
}

void MyTextEdit::AppendContextFromStandErr () {
  this->append (MyProc->readAllStandardError ());
}

void MyTextEdit::AppendContext () {

  QByteArray TempByteArray(MyProc->readAll ());

  QByteArray WinNewLine ("\r\n"), UnixNewLine ("\n");

  TempByteArray.replace (WinNewLine, UnixNewLine);

  QString TempString(TempByteArray);

//  this->append (TempByteArray.toHex ());
//  this->append (TempString);
  this->insertPlainText (TempString);

}

void MyTextEdit::StartCmd () {

  MyProc = new QProcess (this);

//  connect (MyProc, SIGNAL(readyReadStandardOutput ()), this, SLOT(AppendContextFromStandOut ()));
//  connect (MyProc, SIGNAL(readyReadStandardError ()), this, SLOT(AppendContextFromStandErr ()));
  connect (MyProc, SIGNAL(readyRead ()), this, SLOT(AppendContext ()));

  MyProc->start ("ping 168.95.1.1");
}

在繼續補足其它功能的時候，意外發現，我已經把視窗關掉了，為什麼我執行的外部指令還在執行哩~

原因就是，我在main.cpp裡面是宣告一個MyTextEdit的指標變數，並且指到我建立的記憶體空間(new QTextEdit)，當主程式關掉之後，MyTextEdit的指標變數會release給系統(因為，存活的範圍只有在main的{}裡面)，但是，MyTextEdit建立的記憶體空間就不會release給系統，除非delete掉這一個空間。

要解決一個方法，就是在main.cpp裡面，宣告一個物件而不是宣告一個指標來指到一個要求的記憶體位址。
main.cpp

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

int main (
  int argc,
  char *argv[]
  )
{
  QApplication app (argc, argv);

  MyTextEdit TextEdit;

  TextEdit.show ();

  TextEdit.StartCmd ();

  return app.exec ();
}

MyTextEdit.h

#ifndef _MY_TEXT_EDIT_H_
#define _MY_TEXT_EDIT_H_

#include <QTextEdit>

class QProcess;

class MyTextEdit : public QTextEdit {
  Q_OBJECT

  public:
    MyTextEdit (QWidget *parent = 0);
    void StartCmd ();
    bool IsScrollDown ();

  public slots:
    void AppendContext ();
    void MoveScrollDown ();

  private:
    QProcess *MyProc;
};

#endif //#ifndef _MY_TEXT_EDIT_H_

MyTextEdit.cpp

#include "MyTextEdit.h"
#include <QProcess>
#include <QChar>
#include <QScrollBar>
#include <QDebug>

MyTextEdit::MyTextEdit (QWidget *parent) : QTextEdit (parent) {
  MyProc = NULL;
  setReadOnly (true);
//  setTextInteractionFlags (textInteractionFlags() & Qt::NoTextInteraction);
//  setTextInteractionFlags(Qt::TextSelectableByMouse | Qt::TextSelectableByKeyboard);
}

void MyTextEdit::AppendContext () {

  bool KeepDownScroll = false;

  int OrgScrollBarValue = 0;

  //
  // Get the output string
  //
  QByteArray AppendByteArray(MyProc->readAll ());

  //
  // Get the original ScrollBar value
  //
  OrgScrollBarValue = verticalScrollBar ()->value ();

  QByteArray WinNewLine ("\r\n"), UnixNewLine ("\n");

  //
  // Replace "\r\n" by "\n"
  //
  AppendByteArray.replace (WinNewLine, UnixNewLine);

  QString AppendString(AppendByteArray);

//  this->append (AppendByteArray.toHex ());

  if (IsScrollDown ()) {
    if (!(textCursor ().hasSelection () || textCursor ().hasComplexSelection())) {
      //
      // When user select some range or the scroll is already under the buttom
      // set the scroll under the buttom
      //
      KeepDownScroll = true;
    }
  }

  //
  // In order to append string in the end of text
  // have to get the end cursor of the text
  // After append the string, return the cursor to the original status
  //
  QTextCursor EndCursor, OriginalCursor;
  EndCursor = OriginalCursor = textCursor ();
  EndCursor.movePosition (QTextCursor::End);
  setTextCursor (EndCursor);

  //
  // Append the string in the end of text
  //
  insertPlainText (AppendString);

  //
  // return the cursor to the original status
  //
  setTextCursor (OriginalCursor);

  //
  // Set the scrollbar value be the original value
  //
  QScrollBar *ScrollBar = verticalScrollBar ();
  ScrollBar->setValue (OrgScrollBarValue);

  //
  // When user select some range or the scroll is already under the buttom
  // set the scroll under the buttom
  //
  if (KeepDownScroll) {
    MoveScrollDown ();
  }

}

void MyTextEdit::StartCmd () {

  MyProc = new QProcess (this);

  connect (MyProc, SIGNAL(readyRead ()), this, SLOT(AppendContext ()));

  MyProc->start ("ping 168.95.1.1 -t");
}

void MyTextEdit::MoveScrollDown () {

  // Method 1
//  QTextCursor c = textCursor ();
//  c.movePosition (QTextCursor::End);
//  setTextCursor (c);

  // Method 2
  QScrollBar *ScrollBar = verticalScrollBar ();
  ScrollBar->setValue (ScrollBar->maximum ());

}

bool MyTextEdit::IsScrollDown () {

  QScrollBar *ScrollBar = verticalScrollBar ();

  if (ScrollBar->value () == ScrollBar->maximum ()) {
    return true;
  } else {
    return false;
  }
}

結果如下：
1. 當原本右邊的ScrollBar原本就在底部的話，就算文字內容增加，ScrollBar仍會保持在底部

2. 當使用者有圈選內容的話，就算文字內容增加，ScrollBar會保持在原來的位置，若原本的ScrollBar是在底部的話，會因為文字內容增加，而讓ScrollBar離開底部

3. 當使用者移動ScrollBar離開底部時，當文字內容增加，ScrollBar仍會保持在原來的位置。但當使用者把ScrollBar拉回底部時，當文字內容增加，ScrollBar會依然保持在底部。


參考資料：
QT下实现对linux 的Shell 调用 的几种方法 QProcess AND QThread
QTextEdit Class Reference
QProcess Class Reference
QProcess运行外部程序
怎么处理QT的UI界面假死的情况
QT程序 避免假死、无反应现象
QT中使用QProcess启用外部程序||exe
关于窗口调用外部程序及接收返回内容的调试
QT下解决换行符、回车符与Windows不一致的问题
解决QProcess對象調用execute執行cmd命令不支持中文和空格的問題
VCard
Qt - QTextEdit自動捲到底
QT中使用QProcess启用外部程序