Text Finder Example

TextFinder Class Implementation

The TextFinder class's constructor calls the loadUiFile() function and then uses qFindChild() to access the user interface's QWidgets.

 TextFinder::TextFinder(QWidget *parent)
     : QWidget(parent)
 {
     QWidget *formWidget = loadUiFile();

     ui_findButton = qFindChild<QPushButton*>(this, "findButton");
     ui_textEdit = qFindChild<QTextEdit*>(this, "textEdit");
     ui_lineEdit = qFindChild<QLineEdit*>(this, "lineEdit");

We then use QMetaObject's system to enable signal and slot connections.

     QMetaObject::connectSlotsByName(this);

The loadTextFile() function is called to load input.txt into QTextEdit to displays its contents. The TextFinder's layout and window title is set and isFirstTime is set to true.

     loadTextFile();

     QVBoxLayout *layout = new QVBoxLayout;
     layout->addWidget(formWidget);
     setLayout(layout);
     setWindowTitle(tr("Text Finder"));

     isFirstTime = true;
 }

isFirstTime is used as a flag to indicate whether the search operation has been performed more than once. This is further explained with the on_findButton_clicked() function.

The loadUiFile() function is used to load the user interface file previously created in QtDesigner. The QUiLoader class is instantiated and its load() function is used to load the form into formWidget that acts as a place holder for the user interface. The function then returns formWidget to its caller.

 QWidget* TextFinder::loadUiFile()
 {
     QUiLoader loader;

     QFile file(":/forms/textfinder.ui");
     file.open(QFile::ReadOnly);

     QWidget *formWidget = loader.load(&file, this);
     file.close();

     return formWidget;
 }

As mentioned earlier, the loadTextFile() function loads input.txt into QTextEdit to display its contents. Data is read using QTextStream into a QString object, line with the QTextStream::readAll() function. The contents of line are then appended to ui_textEdit.

 void TextFinder::loadTextFile()
 {
     QFile inputFile(":/forms/input.txt");
     inputFile.open(QIODevice::ReadOnly);
     QTextStream in(&inputFile);
     QString line = in.readAll();
     inputFile.close();

     ui_textEdit->append(line);
     ui_textEdit->setUndoRedoEnabled(false);
     ui_textEdit->setUndoRedoEnabled(true);
 }

The on_findButton_clicked() function is a slot that is connected to ui_findButton's clicked() signal. The searchString is extracted from the ui_lineEdit and the document is extracted from textEdit. In event there is an empty searchString, a QMessageBox is used, requesting the user to enter a word. Otherwise, we traverse through the words in ui_textEdit, and highlight all ocurrences of the searchString . Two QTextCursor objects are used: One to traverse through the words in line and another to keep track of the edit blocks.

 void TextFinder::on_findButton_clicked()
 {
     QString searchString = ui_lineEdit->text();
     QTextDocument *document = ui_textEdit->document();

     bool found = false;

     if (isFirstTime == false)
         document->undo();

     if (searchString == "") {
         QMessageBox::information(this, tr("Empty Search Field"),
                 "The search field is empty. Please enter a word and click Find.");
     } else {

         QTextCursor highlightCursor(document);
         QTextCursor cursor(document);

         cursor.beginEditBlock();

         QTextCharFormat plainFormat(highlightCursor.charFormat());
         QTextCharFormat colorFormat = plainFormat;
         colorFormat.setForeground(Qt::red);

         while (!highlightCursor.isNull() && !highlightCursor.atEnd()) {
             highlightCursor = document->find(searchString, highlightCursor, QTextDocument::FindWholeWords);

             if (!highlightCursor.isNull()) {
                 found = true;
                 highlightCursor.movePosition(QTextCursor::WordRight,
                                        QTextCursor::KeepAnchor);
                 highlightCursor.mergeCharFormat(colorFormat);
             }
         }

         cursor.endEditBlock();

The isFirstTime flag is set to false the moment findButton is clicked. This is necessary to undo the previous text highlight before highlighting the user's next search string. Also, the found flag is used to indicate if the searchString was found within the contents of ui_textEdit. If it was not found, a QMessageBox is used to inform the user.

         isFirstTime = false;

         if (found == false) {
             QMessageBox::information(this, tr("Word Not Found"),
                 "Sorry, the word cannot be found.");
         }
     }
 }

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

     TextFinder *textFinder = new TextFinder;
     textFinder->show();

     return app.exec();
 }