Common Methods of QLineEdit in Qt

In Qt, QLineEdit is a widget used for single-line text input, and it provides various methods to set, retrieve, and manipulate text input. Here’s a detailed explanation of some common methods and functionalities of QLineEdit:

1. Constructor:

   • You can create a QLineEdit using different constructors, typically specifying the parent window (parent widget), and optionally providing initial text in the constructor.

   QLineEdit *lineEdit = new QLineEdit(parentWidget);
   lineEdit->setText("Initial Text");
   

• Set Text (setText):

  • The setText method is used to set text as the initial or subsequent content of the QLineEdit.

  lineEdit->setText("New Text");
  

• Get Text (text):

  • The text method is used to retrieve the current text in the QLineEdit.

  QString currentText = lineEdit->text();
  

• Clear Text (clear):

  • The clear method is used to remove all text from the QLineEdit, making it empty.

  lineEdit->clear();
  

• Set Maximum Input Length (setMaxLength):

  • The setMaxLength method is used to limit the number of characters that can be entered in the QLineEdit.

  lineEdit->setMaxLength(50); // Set the maximum length to 50 characters
  

• Set Placeholder Text (setPlaceholderText):

  • The setPlaceholderText method is used to set placeholder text that is displayed when the QLineEdit is empty.

  lineEdit->setPlaceholderText("Enter your name");
  

• Signals and Slots:

  • QLineEdit emits various signals, such as the textChanged signal, which can be used to listen to text change events. You can connect these signals to custom slot functions to handle text changes.

  connect(lineEdit, SIGNAL(textChanged(const QString &)), this, SLOT(handleTextChanged(const QString &)));
  

• Edit and Read-Only Modes (setReadOnly):

  • The setReadOnly method is used to set QLineEdit in edit mode or read-only mode, determining whether users are allowed to edit the text.

  lineEdit->setReadOnly(true); // Set to read-only mode
  lineEdit->setReadOnly(false); // Set to edit mode