1 背景

Qt5 中有个很基本的单行输入框控件，就是 QLineEdit，类似于HTML中的input标签。

在QCAD开源项目中，其主界面中有个供用户输入绘图命令的单行输入框控件，其可以实现类似 Linux 终端的简单效果：

1. 上键显示最近的一条命令
2. 上下键在历史命令里面查找命令
3.  Ctrl+V键粘贴命令
4.  Ctrl+L键清空命令

功能简单，但是也算是看到了 Qt 的较中级的用法，就是继承和扩展Qt 原生组件。

2 代码说明

首先继承 QLineEdit 类。

新增了两个字段/属性，用于存储命令的字符串列表 history，还有一个迭代器 it，指代命令在列表中的位置。

重载 keyPressEvent 函数，用于支持自定义的Up，Down，Ctrl+V，Ctrl+L按键事件。

注意：源代码非完整代码，无法运行。

3 源代码

3.1 头文件 RCommandLine.h

/*** Copyright (c) 2011-2018 by Andrew Mustun. All rights reserved.* * This file is part of the QCAD project.** QCAD is free software: you can redistribute it and/or modify* it under the terms of the GNU General Public License as published by* the Free Software Foundation, either version 3 of the License, or* (at your option) any later version.** QCAD is distributed in the hope that it will be useful,* but WITHOUT ANY WARRANTY; without even the implied warranty of* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the* GNU General Public License for more details.** You should have received a copy of the GNU General Public License* along with QCAD.*/#ifndef RCOMMANDLINE_H_
#define RCOMMANDLINE_H_#include "gui_global.h"#include 
#include 
#include 
#include /*** \scriptable* \ingroup gui*/
class QCADGUI_EXPORT RCommandLine: public QLineEdit {Q_OBJECTsignals:void clearHistory();void commandConfirmed(const QString& command);void completeCommand(const QString& command);void escape();public:RCommandLine(QWidget* parent = 0);QString getLastCommand();void appendCommand(const QString& cmd);QStringList getHistory() const;void setHistory(QStringList& h);void triggerCommand(const QString& cmd) {emit commandConfirmed(cmd);}public slots:void paste();protected:virtual void keyPressEvent(QKeyEvent* event);virtual bool event(QEvent* event);private:QStringList history;QStringList::iterator it;
};Q_DECLARE_METATYPE(RCommandLine*)#endif

3.2  RCommandLine.cpp

/*** Copyright (c) 2011-2018 by Andrew Mustun. All rights reserved.* * This file is part of the QCAD project.** QCAD is free software: you can redistribute it and/or modify* it under the terms of the GNU General Public License as published by* the Free Software Foundation, either version 3 of the License, or* (at your option) any later version.** QCAD is distributed in the hope that it will be useful,* but WITHOUT ANY WARRANTY; without even the implied warranty of* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the* GNU General Public License for more details.** You should have received a copy of the GNU General Public License* along with QCAD.*/
#include 
#include 
#include 
#include #if QT_VERSION >= 0x050000#include 
#else#include 
#endif#include "RCommandLine.h"
#include "RDebug.h"RCommandLine::RCommandLine(QWidget* parent) :QLineEdit(parent), it(history.end()) {
}QString RCommandLine::getLastCommand() {if (history.isEmpty()) {return QString();}return history.last();
}void RCommandLine::appendCommand(const QString& cmd) {if (!cmd.isEmpty() && (history.isEmpty() || history.last() != cmd)) {history.append(cmd);}it = history.end();
}QStringList RCommandLine::getHistory() const {return history;
}void RCommandLine::setHistory(QStringList& h) {history = h;it = history.end();
}void RCommandLine::paste() {
#if QT_VERSION >= 0x050000QClipboard* cb = QGuiApplication::clipboard();
#elseQClipboard* cb = QApplication::clipboard();
#endif//qDebug("pasting: " + cb.text());QString text = cb->text();// multi line paste and enter:if (text.contains("\n")) {QStringList lines = text.split('\n');for (int i=0; itype() == QEvent::KeyPress) {QKeyEvent* ke = dynamic_cast (event);if (ke->key() == Qt::Key_Tab) {emit completeCommand(text());return true;}}return QLineEdit::event(event);
}void RCommandLine::keyPressEvent(QKeyEvent* event) {switch (event->key()) {case Qt::Key_L:if (event->modifiers() == Qt::ControlModifier) {emit clearHistory();return;}break;case Qt::Key_V:if (event->modifiers() == Qt::ControlModifier) {paste();return;}break;case Qt::Key_Enter:case Qt::Key_Return: {QString t = text();
//        if (!t.isEmpty() && (history.isEmpty() || history.last() != t)) {
//            history.append(t);
//        }it = history.end();emit commandConfirmed(t);}break;case Qt::Key_Up:if (it != history.begin()) {it--;setText(*it);}return;break;case Qt::Key_Down:if (it != history.end()) {it++;if (it != history.end()) {setText(*it);} else {clear();}}return;break;default:break;}QLineEdit::keyPressEvent(event);
}

以上源代码仅供学习交流，版权归QCAD项目所有。