Qt是目前最先进、最完整的跨平台C开发工具。它不仅完全实现了一次编写所有平台无差别运行更提供了几乎所有开发过程中需要用到的工具。如今Qt已被运用于超过70个行业、数千家企业支持数百万设备及应用。Line Edits行编辑示例演示了QLineEdit的多种使用方式并显示了各种属性和验证器对用户提供的输入和输出的影响。该示例由单个Window类组成其中包含具有不同输入约束和显示属性的行编辑选择这些属性可以通过从组合框中选择项来更改。将它们放在一起可以帮助开发人员选择合适的属性用于行编辑并且可以很容易地比较每个验证器对用户输入的影响。Window类定义Window类继承了QWidget并包含一个构造函数和几个槽class Window : public QWidget { Q_OBJECT public: Window(QWidget *parent nullptr); public slots: void echoChanged(int); void validatorChanged(int); void alignmentChanged(int); void inputMaskChanged(int); void accessChanged(int); private: QLineEdit *echoLineEdit; QLineEdit *validatorLineEdit; QLineEdit *alignmentLineEdit; QLineEdit *inputMaskLineEdit; QLineEdit *accessLineEdit; };当在关联的组合框中选择了新的验证器时这些槽用于更新给定行编辑的验证器类型行编辑保存在窗口中以便在这些槽中使用。Window类实现Window构造函数用于设置行编辑器、验证器和组合框将来自组合框的信号连接到Window类中的槽并在布局中安排子部件。我们首先构建一个组框来保存标签、组合框和行编辑器这样就可以演示QLineEdit::echoMode属性Window::Window(QWidget *parent) : QWidget(parent) { QGroupBox *echoGroup new QGroupBox(tr(Echo)); QLabel *echoLabel new QLabel(tr(Mode:)); QComboBox *echoComboBox new QComboBox; echoComboBox-addItem(tr(Normal)); echoComboBox-addItem(tr(Password)); echoComboBox-addItem(tr(PasswordEchoOnEdit)); echoComboBox-addItem(tr(No Echo)); echoLineEdit new QLineEdit; echoLineEdit-setPlaceholderText(Placeholder Text); echoLineEdit-setFocus();在这一点上这些小部件都没有被安排在布局中。最后echoLabel、echoComboBox和echoLineEdit将被放置在echoGroup组框内的垂直布局中。类似地我们构造组框和小部件集合来显示QIntValidator 和QDoubleValidator对行编辑器内容的影响QGroupBox *validatorGroup new QGroupBox(tr(Validator)); QLabel *validatorLabel new QLabel(tr(Type:)); QComboBox *validatorComboBox new QComboBox; validatorComboBox-addItem(tr(No validator)); validatorComboBox-addItem(tr(Integer validator)); validatorComboBox-addItem(tr(Double validator)); validatorLineEdit new QLineEdit; validatorLineEdit-setPlaceholderText(Placeholder Text);文本对齐由另一组小部件演示QGroupBox *alignmentGroup new QGroupBox(tr(Alignment)); QLabel *alignmentLabel new QLabel(tr(Type:)); QComboBox *alignmentComboBox new QComboBox; alignmentComboBox-addItem(tr(Left)); alignmentComboBox-addItem(tr(Centered)); alignmentComboBox-addItem(tr(Right)); alignmentLineEdit new QLineEdit; alignmentLineEdit-setPlaceholderText(Placeholder Text);QLineEdit 支持使用输入掩码它们只允许用户在行编辑中输入遵循简单规范的字符我们构建了一组小部件来演示预定义掩码的选择QGroupBox *inputMaskGroup new QGroupBox(tr(Input mask)); QLabel *inputMaskLabel new QLabel(tr(Type:)); QComboBox *inputMaskComboBox new QComboBox; inputMaskComboBox-addItem(tr(No mask)); inputMaskComboBox-addItem(tr(Phone number)); inputMaskComboBox-addItem(tr(ISO date)); inputMaskComboBox-addItem(tr(License key)); inputMaskLineEdit new QLineEdit; inputMaskLineEdit-setPlaceholderText(Placeholder Text);QLineEdit的另一个有用特性是使其内容只读的能力此属性用于控制对以下小部件组中的行编辑访问QGroupBox *accessGroup new QGroupBox(tr(Access)); QLabel *accessLabel new QLabel(tr(Read-only:)); QComboBox *accessComboBox new QComboBox; accessComboBox-addItem(tr(False)); accessComboBox-addItem(tr(True)); accessLineEdit new QLineEdit; accessLineEdit-setPlaceholderText(Placeholder Text);现在所有的子部件都已经构造好了我们将来自组合框的信号连接到Window对象中的槽connect(echoComboBox, QComboBox::activated, this, Window::echoChanged); connect(validatorComboBox, QComboBox::activated, this, Window::validatorChanged); connect(alignmentComboBox, QComboBox::activated, this, Window::alignmentChanged); connect(inputMaskComboBox, QComboBox::activated, this, Window::inputMaskChanged); connect(accessComboBox, QComboBox::activated, this, Window::accessChanged);这些连接中的每一个都使用QComboBox::activated()信号该信号向插槽提供一个整数这将用于有效地更改每个槽中的适当行编辑。我们将每个组合框、行编辑和标签放置在每个组框的布局中从echoGroup组框的布局开始QGridLayout *echoLayout new QGridLayout; echoLayout-addWidget(echoLabel, 0, 0); echoLayout-addWidget(echoComboBox, 0, 1); echoLayout-addWidget(echoLineEdit, 1, 0, 1, 2); echoGroup-setLayout(echoLayout);其他布局的构造方式相同QGridLayout *validatorLayout new QGridLayout; validatorLayout-addWidget(validatorLabel, 0, 0); validatorLayout-addWidget(validatorComboBox, 0, 1); validatorLayout-addWidget(validatorLineEdit, 1, 0, 1, 2); validatorGroup-setLayout(validatorLayout); QGridLayout *alignmentLayout new QGridLayout; alignmentLayout-addWidget(alignmentLabel, 0, 0); alignmentLayout-addWidget(alignmentComboBox, 0, 1); alignmentLayout-addWidget(alignmentLineEdit, 1, 0, 1, 2); alignmentGroup- setLayout(alignmentLayout); QGridLayout *inputMaskLayout new QGridLayout; inputMaskLayout-addWidget(inputMaskLabel, 0, 0); inputMaskLayout-addWidget(inputMaskComboBox, 0, 1); inputMaskLayout-addWidget(inputMaskLineEdit, 1, 0, 1, 2); inputMaskGroup-setLayout(inputMaskLayout); QGridLayout *accessLayout new QGridLayout; accessLayout-addWidget(accessLabel, 0, 0); accessLayout-addWidget(accessComboBox, 0, 1); accessLayout-addWidget(accessLineEdit, 1, 0, 1, 2); accessGroup-setLayout(accessLayout);最后我们将每个组框放置在Window对象的网格布局中并设置窗口标题QGridLayout *layout new QGridLayout; layout-addWidget(echoGroup, 0, 0); layout-addWidget(validatorGroup, 1, 0); layout-addWidget(alignmentGroup, 2, 0); layout-addWidget(inputMaskGroup, 0, 1); layout-addWidget(accessGroup, 1, 1); setLayout(layout); setWindowTitle(tr(Line Edits)); }槽响应用户更改组合框时发出的信号。当Echo分组框的组合框被改变时echoChanged()槽被调用void Window::echoChanged(int index) { switch (index) { case 0: echoLineEdit-setEchoMode(QLineEdit::Normal); break; case 1: echoLineEdit-setEchoMode(QLineEdit::Password); break; case 2: echoLineEdit-setEchoMode(QLineEdit::PasswordEchoOnEdit); break; case 3: echoLineEdit-setEchoMode(QLineEdit::NoEcho); break; } }槽更新同一分组框中的行编辑来使用与分组合框中描述的条目对应的回显模式。当Validator分组框的组合框被改变时validatorChanged()槽被调用void Window::validatorChanged(int index) { switch (index) { case 0: validatorLineEdit-setValidator(nullptr); break; case 1: validatorLineEdit-setValidator(new QIntValidator( validatorLineEdit)); break; case 2: validatorLineEdit-setValidator(new QDoubleValidator(-999.0, 999.0, 2, validatorLineEdit)); break; } validatorLineEdit-clear(); }槽或者为要使用的行编辑创建一个新的验证器或者通过调用带有零指针的QLineEdit::setValidator()来删除正在使用的验证器。在本例中我们清除了行编辑以确保最初为新的验证器提供了有效的输入。当对齐分组框的组合框被改变时alignmentChanged()槽被调用void Window::alignmentChanged(int index) { switch (index) { case 0: alignmentLineEdit-setAlignment(Qt::AlignLeft); break; case 1: alignmentLineEdit-setAlignment(Qt::AlignCenter); break; case 2: alignmentLineEdit-setAlignment(Qt::AlignRight); break; } }这会改变文本在行编辑器中的显示方式使其与组合框中选择的描述相对应。inputMaskChanged()插槽处理输入掩码分组框中组合框的更改void Window::inputMaskChanged(int index) { switch (index) { case 0: inputMaskLineEdit-setInputMask(); break; case 1: inputMaskLineEdit-setInputMask(99 99 99 99 99;_); break; case 2: inputMaskLineEdit-setInputMask(0000-00-00); inputMaskLineEdit-setText(00000000); inputMaskLineEdit-setCursorPosition(0); break; case 3: inputMaskLineEdit-setInputMask(AAAAA-AAAAA-AAAAA-AAAAA-AAAAA;#); break; } }相关组合框中的每个条目都与一个输入掩码相关联我们通过使用合适的字符串调用QLineEdit::setInputMask()函数来设置一个新的掩码如果使用空字符串则禁用掩码。accessChanged()槽处理Access分组框中组合框的更改void Window::accessChanged(int index) { switch (index) { case 0: accessLineEdit-setReadOnly(false); break; case 1: accessLineEdit-setReadOnly(true); break; } }这里我们简单地将分组合框中的False和True条目与传递给QLineEdit::setReadOnly()的False和True值关联起来这允许用户启用和禁用对行编辑的输入。