Qt——QLineEdit使用总结

QLineEdit是一个单行文本编辑控件。

使用者可以通过很多函数，输入和编辑单行文本，比如撤销、恢复、剪切、粘贴以及拖放等。

通过改变QLineEdit的 echoMode() ，可以设置其属性，比如以密码的形式输入。

文本的长度可以由 maxLength() 限制，可以通过使用 validator() 或者 inputMask() 可以限制它只能输入数字。在对同一个QLineEdit的validator或者input mask进行转换时，最好先将它的validator或者input mask清除，以避免错误发生。

与QLineEdit相关的一个类是QTextEdit，它允许多行文字以及富文本编辑。

我们可以使用 setText() 或者 insert() 改变其中的文本，通过 text() 获得文本，通过 displayText() 获得显示的文本，使用 setSelection() 或者 selectAll() 选中文本，选中的文本可以通过cut()、copy()、paste()进行剪切、复制和粘贴，使用 setAlignment() 设置文本的位置。

文本改变时会发出 textChanged() 信号；如果不是由setText()造成文本的改变，那么会发出textEdit()信号；鼠标光标改变时会发出cursorPostionChanged()信号；当返回键或者回车键按下时，会发出returnPressed()信号。

当编辑结束，或者LineEdit失去了焦点，或者当返回/回车键按下时，editFinished()信号将会发出。

以上是Qt官方文档对QLineEdit的简要说明，下面根据个人经验，对一些常用的方法作说明：

1.setPlaceholderText()设置提示文字

豆瓣电影的搜索输入框，没有输入任何字符时，显示“电影、影人、影院、电视剧”这些占位文字，对用户输入作相关提示。

echoLineEdit->setPlaceholderText( "电影、影人、影院、电视剧" );

 2.setEchoMode()设置模式

淘宝登录界面的一部分，用户名可以直接看到，密码一般都用小黑点掩盖。

switch  (index) {
    case  0:
        //默认，输入什么即显示什么
        echoLineEdit->setEchoMode(QLineEdit::Normal);
        break ;
    case  1:
        //密码，一般是用小黑点覆盖你所输入的字符
        echoLineEdit->setEchoMode(QLineEdit::Password);
        break ;
    case  2:
        //编辑时输入字符显示输入内容，否则用小黑点代替
        echoLineEdit->setEchoMode(QLineEdit::PasswordEchoOnEdit);
        break ;
    case  3:
        //任何输入都看不见（只是看不见，不是不能输入）
        echoLineEdit->setEchoMode(QLineEdit::NoEcho);
    }

3.setAlignment()设置文本位置

switch  (index) {
    case  0:
        alignmentLineEdit->setAlignment(Qt::AlignLeft);
        break ;
    case  1:
        alignmentLineEdit->setAlignment(Qt::AlignCenter);
        break ;
    case  2:
        alignmentLineEdit->setAlignment(Qt::AlignRight);
    }

4.setReadOnly()设置能否编辑

switch  (index) {
    case  0:
        accessLineEdit->setReadOnly( false );
        break ;
    case  1:
        accessLineEdit->setReadOnly( true );
    }

 5.setValidator()对输入进行限制

这种方式的实质是通过正则表达式限制输入的内容。

比如上面的手机号输入框，控制其不能输入英文汉字等无关字符。

switch  (index) {
    case  0:
        //无限制
        validatorLineEdit->setValidator(0);
        break ;
    case  1:
        //只能输入整数
        validatorLineEdit->setValidator( new  QIntValidator(
            validatorLineEdit));
        break ;
    case  2:
        //实例，只能输入-180到180之间的小数，小数点后最多两位（可用于限制经纬度等）
        QDoubleValidator *pDfValidator =  new  QDoubleValidator(-180.0, 180.0 , 2, validatorLineEdit);
        pDfValidator->setNotation(QDoubleValidator::StandardNotation);
        validatorLineEdit->setValidator(pDfValidator);
    }

6.setInputMask()对输入进行限制

通过限制格式限制输入，具体怎么格式化可以参考Qt助手。

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;#" );
    }

7.setMaxLength()设置可以输入的最多字符数

//最多只能输入9个字符
echoLineEdit->setMaxLength(9);

8.validator和inputmask的结合

比如纬度用“度:分:秒”的格式表示，分和秒的范围都是00-59，度的范围是-89到89。

QRegExp rx( "(-|\\+)?[0-8]\\d:[0-5]\\d:[0-5]\\d" );
echoLineEdit->setValidator( new  QRegExpValidator(rx, echoLineEdit));
echoLineEdit->setInputMask( "#00:00:00;0" );
echoLineEdit->setText( "+00:00:00" );

如果不控制输入，那么必须在输入后检查输入是否合法，但控制输入后的输入肯定是合法的，可以省去检查合法的繁琐步骤。只需使用正则表达式控制输入的度分秒范围，然后控制输入的格式。

 

一些测试代码供参考——

头文件：

#ifndef WINDOW_H
#define WINDOW_H

#include

QT_BEGIN_NAMESPACE
class  QComboBox;
class  QLineEdit;
QT_END_NAMESPACE

//! [0]
class  Window :  public  QWidget
{
    Q_OBJECT

public :
    Window();

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;
};
//! [0]

#endif

 

实现：

#include

#include "window.h"

//! [0]
Window::Window()
{
    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;
    //test
    /*QRegExp rx("(-|\\+)?[0-8]\\d:[0-5]\\d:[0-5]\\d");
    echoLineEdit->setValidator(new QRegExpValidator(rx, echoLineEdit));
    echoLineEdit->setInputMask("#00:00:00;0");
    echoLineEdit->setText("+00:00:00");*/

    //echoLineEdit->setMaxLength(9);
    echoLineEdit->setPlaceholderText( "电影、影人、影院、电视剧" );
    echoLineEdit->setFocus();
//! [0]

//! [1]
    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" );
//! [1]

//! [2]
    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" );
//! [2]

//! [3]
    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" );
//! [3]

//! [4]
    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" );
//! [4]

//! [5]
    connect(echoComboBox, SIGNAL(activated( int )),
            this , SLOT(echoChanged( int )));
    connect(validatorComboBox, SIGNAL(activated( int )),
            this , SLOT(validatorChanged( int )));
    connect(alignmentComboBox, SIGNAL(activated( int )),
            this , SLOT(alignmentChanged( int )));
    connect(inputMaskComboBox, SIGNAL(activated( int )),
            this , SLOT(inputMaskChanged( int )));
    connect(accessComboBox, SIGNAL(activated( int )),
            this , SLOT(accessChanged( int )));
//! [5]

//! [6]
    QGridLayout *echoLayout =  new  QGridLayout;
    echoLayout->addWidget(echoLabel, 0, 0);
    echoLayout->addWidget(echoComboBox, 0, 1);
    echoLayout->addWidget(echoLineEdit, 1, 0, 1, 2);
    echoGroup->setLayout(echoLayout);
//! [6]

//! [7]
    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);
//! [7]

//! [8]
    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" ));
}
//! [8]

//! [9]
void  Window::echoChanged( int  index)
{
    switch  (index) {
    case  0:
        //默认，输入什么即显示什么
        echoLineEdit->setEchoMode(QLineEdit::Normal);
        break ;
    case  1:
        //密码，一般是用小黑点覆盖你所输入的字符
        echoLineEdit->setEchoMode(QLineEdit::Password);
        break ;
    case  2:
        //编辑时输入字符显示输入内容，否则用小黑点代替
        echoLineEdit->setEchoMode(QLineEdit::PasswordEchoOnEdit);
        break ;
    case  3:
        //任何输入都看不见（只是看不见，不是不能输入）
        echoLineEdit->setEchoMode(QLineEdit::NoEcho);
    }
}
//! [9]

//! [10]
void  Window::validatorChanged( int  index)
{
    switch  (index) {
    case  0:
        //无限制
        validatorLineEdit->setValidator(0);
        break ;
    case  1:
        //只能输入整数
        validatorLineEdit->setValidator( new  QIntValidator(
            validatorLineEdit));
        break ;
    case  2:
        //实例，只能输入-180到180之间的小数，小数点后最多两位（可用于限制经纬度等）
        QDoubleValidator *pDfValidator =  new  QDoubleValidator(-180.0, 180.0 , 2, validatorLineEdit);
        pDfValidator->setNotation(QDoubleValidator::StandardNotation);
        validatorLineEdit->setValidator(pDfValidator);
    }

    validatorLineEdit->clear();
}
//! [10]

//! [11]
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);
    }
}
//! [11]

//! [12]
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;#" );
    }
}
//! [12]

//! [13]
void  Window::accessChanged( int  index)
{
    switch  (index) {
    case  0:
        accessLineEdit->setReadOnly( false );
        break ;
    case  1:
        accessLineEdit->setReadOnly( true );
    }
}
//! [13]