Question

The code below does not highlight the search term when it is found. In fact the cursor disappears from the QPlainTextEdit (called ui->Editor) after pressing the ‘next’ button. What’s causing it?

void TextEditor::findNextInstanceOfSearchTerm()
{
    QString searchTerm = this->edtFind->text();

    if(this->TextDocument == NULL)
    {
        this->TextDocument = ui->Editor->document();
    }


    QTextCursor documentCursor(this->TextDocument);

    documentCursor = this->TextDocument->find(searchTerm,documentCursor);

    if(!documentCursor.isNull())
    {
        documentCursor.select(QTextCursor::WordUnderCursor);

    }else
    {
        ui->statusbar->showMessage("\""+searchTerm+"\" could not be found",MESSAGE_DURATION);

    }
}

Answer 1

Firstly, your code creates a new cursor at the beginning of the document each time you press the next button, so you will always search from the beginning. Secondly, you must understand that the cursor you manipulate has nothing to do with the one in your QPlainTextEdit: you manipulate a copy. If you want to impact the text edit, you must modify its cursor using setTextCursor. Here is a working solution:

void TextEditor::findNextInstanceOfSearchTerm()
{
    QString searchTerm = this->edtFind->text();

    if(this->TextDocument == NULL)
    {
        this->TextDocument = ui->Editor->document();
    }

    // get the current cursor
    QTextCursor documentCursor = ui->Editor->textCursor();

    documentCursor = this->TextDocument->find(searchTerm,documentCursor);

    if(!documentCursor.isNull())
    {
        // needed only if you want the entire word to be selected
        documentCursor.select(QTextCursor::WordUnderCursor);

        // modify the text edit cursor
        ui->Editor->setTextCursor(documentCursor);
    }
    else
    {
        ui->statusbar->showMessage(
            "\""+searchTerm+"\" could not be found",MESSAGE_DURATION);
    }
}

As a side note, you might want to know that QPlainTextEdit provides a find method, so this might be an easier way to achieve what you want:

void TextEditor::findNextInstanceOfSearchTerm()
{
    QString searchTerm = this->edtFind->text();

    bool found = ui->Editor->find(searchTerm);

    if (found)
    {
        QTextCursor cursor = ui->Editor->textCursor();
        cursor.select(QTextCursor::WordUnderCursor);
        ui->Editor->setTextCursor(cursor);
    }
    else
    {
        // set message in status bar
    }
}