Text Finder Example¶
Dynamically loading .ui files using
QUiLoader
.The TextFinder example shows how to load and setup a
.ui
file dynamically using theQUiLoader
class that is part of the Qt UI Tools library.The program allows the user to look up a particular word within the contents of a text. The visual elements and layout of the user interface is loaded at runtime, from a the program resources.
Setting Up The Resource File¶
The resources required for the example are:
textfinder.ui
- the user interface file created in Qt Designer
input.txt
- a text file containing some text to be displayed in aQTextEdit
textfinder.ui
contains all the necessaryQWidget
objects for the Text Finder. AQLineEdit
is used for the user input, aQTextEdit
is used to display the contents ofinput.txt
, aQLabel
is used to display the text “Keyword”, and aQPushButton
is used for the Find button. Note that all the widgets have sensibleobjectName
‘s assigned. These are used in code to identify them.The screenshot below shows the preview obtained in Qt Designer.
In this example, we store both resources in the applicaton’s executable by including the
textfinder.qrc
file. Alternatively, the files could also be loaded at runtime from the file system, or from an external binary resource.rcc
file. For more information on resource files, see The Qt Resource System .The
textfinder.qrc
file lists all files that should be included as a resource:<Code snippet "/data/snapshot-qt5full-5.15/qt5/qtbase/textfinder/textfinder.qrc" not found>To generate a form at run-time, the example is linked against the Qt Ui Tools library. This is done in the
textfinder.pro
file:<Code snippet "textfinder/textfinder.pro:0" not found>
TextFinder Class Definition¶
The
TextFinder
class contains the main user interface. It declares pointers to theQPushButton
,QTextEdit
andQLineEdit
elements described above. TheQLabel
in the user interface is not declared here as we do not need to access it from code.class TextFinder : public QWidget { Q_OBJECT public: explicit TextFinder(QWidget *parent = nullptr); private slots: void on_findButton_clicked(); private: QPushButton *ui_findButton; QTextEdit *ui_textEdit; QLineEdit *ui_lineEdit; };The slot
on_findButton_clicked()
is a slot named according to the Automatic Connection naming convention required byuic
.
Loading the Resources¶
We use
QFile
to load the data from the program resources at runtime. The code for this is in two method methods on top oftextfinder.cpp
:loadUiFile
andloadTextFile
.The
loadUiFile
function loads the user interface file previously created in Qt Designer. First, the content of thetextfinder.ui
file is loaded from the resource system. Then aQUiLoader
instance is created, and theload()
function is called, with the first argument being the open file, and the second argument being the pointer of the widget that should be set as the parent. The createdQWidget
is returned.static QWidget *loadUiFile(QWidget *parent) { QFile file(":/forms/textfinder.ui"); file.open(QIODevice::ReadOnly); QUiLoader loader; return loader.load(&file, parent); }In a similar vein, the
loadTextFile
function loadsinput.txt
from the resources. Data is read usingQTextStream
into aQString
with thereadAll()
function. We explicitly set the encoding to UTF-8 , becauseQTextStream
by default uses the current system locale. Finally, the loaded text is returned.static QString loadTextFile() { QFile inputFile(":/forms/input.txt"); inputFile.open(QIODevice::ReadOnly); QTextStream in(&inputFile); in.setCodec("UTF-8"); return in.readAll(); }
TextFinder Class Implementation¶
The
TextFinder
class’s constructor does not instantiate any child widgets directly. Instead, it calls theloadUiFile()
function, and then usesfindChild()
to locate the createdQWidget
s by object name.TextFinder::TextFinder(QWidget *parent) : QWidget(parent) { QWidget *formWidget = loadUiFile(this); ui_findButton = findChild<QPushButton*>("findButton"); ui_textEdit = findChild<QTextEdit*>("textEdit"); ui_lineEdit = findChild<QLineEdit*>("lineEdit");We then use
connectSlotsByName()
to enable the automatic calling of theon_findButton_clicked()
slot.QMetaObject::connectSlotsByName(this);The
loadTextFile
function is called to get the text to be shown in theQTextEdit
.ui_textEdit->setText(loadTextFile());The dynamically loaded user interface in
formWidget
is now properly set up. We now embedformWidget
through aQVBoxLayout
.QVBoxLayout *layout = new QVBoxLayout; layout->addWidget(formWidget); setLayout(layout);At the end of the constructor we set a window title.
setWindowTitle(tr("Text Finder")); }The
on_findButton_clicked()
function is a slot that is connected toui_findButton
‘sclicked()
signal. ThesearchString
is extracted from theui_lineEdit
and thedocument
is extracted fromui_textEdit
. If there is an emptysearchString
, aQMessageBox
is used, requesting the user to enter a word. Otherwise, we traverse through the words inui_textEdit
, and highlight all ocurrences of thesearchString
. TwoQTextCursor
objects are used: One to traverse through the words inline
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; // undo previous change (if any) document->undo(); if (searchString.isEmpty()) { QMessageBox::information(this, tr("Empty Search Field"), tr("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
found
flag is used to indicate if thesearchString
was found within the contents ofui_textEdit
. If it was not found, aQMessageBox
is used to inform the user.if (found == false) { QMessageBox::information(this, tr("Word Not Found"), tr("Sorry, the word cannot be found.")); } } }
main()
Function¶
The
main()
function instantiates and showsTextFinder
.int main(int argc, char *argv[]) { QApplication app(argc, argv); TextFinder textFinder; textFinder.show(); return app.exec(); }There are various approaches to include forms into applications. Using QUILoader is just one of them. See Using a Designer UI File in Your Application for more information on the other approaches available.
See also
Calculator Builder ExampleWorld Time Clock Builder Example
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