File management and standard dialog box in Qt

QDir class has the ability to access directory structure and content. It can operate directories, access directory or file information, operate the underlying file system, and access Qt resource files.

To determine whether a directory exists, you can use exists(), and the attributes of the directory can be obtained using isReadable(), isAbsolute (), isRelative(), and isRoot().

There are many entries in the directory, including files, directories and symbolic connections,

The total number of entries can be counted using count().

entryList() returns a string linked list of all entries in the directory.

The file can be deleted using the remove() function,

Delete the directory with rmdir(),

Rename with rename().

Filters are generally used to filter the files in the directory.

QFileInfo:

QFilelnfo class provides system independent file information, including file name, location (path) in the file system, file access permission, whether it is a directory or symbolic link, etc. QFilelnfo can also obtain the file size and the last modification / reading time, as well as the relevant information of Qt resources.

The file pointed to by QFilelnfo can be set when the QFileinfo object is built, or set later using setFile(). You can use exists() to see if the file exists, and size() to get the size of the file.

1.2. Judge whether the folder exists

QDir dir("D:/qtmode");//The absolute path, or relative path, is where the project's build directory begins
qDebug()<<dir.exists();//Return false if none, return true if none

1.3. Create directory

QDir dir("D:/test");
if(!dir.exists())
{
    dir.mkdir("D:/test");
    qDebug()<<"A new folder was created";
}
else
{
    qDebug()<<"Folder exists";
}

1.4. Obtain common directories

Code:

QDir dir;
    qDebug()<<dir.current()<<endl;
    qDebug()<<dir.currentPath()<<endl;
    qDebug()<<dir.homePath()<<endl;
    qDebug()<<dir.tempPath()<<endl;
    qDebug()<<dir.rootPath();

Demonstration effect:

1.5. Switching path

QDir dir("D:/text");
qDebug()<<dir.dirName();//The name of the current folder
qDebug()<<dir.absolutePath();//The absolute path of the current folder
dir.cd("C:/");//Switch to drive C
qDebug()<<dir.absolutePath();

1.6. Traversing files

QDir dir(dir.current());
foreach(QFileInfo item,dir.entryInfoList())
{
    if(item.isDir())
    {
       qDebug()<<"folder:"<<item.filePath(); //fileName only has the name of the file (folder)
    }else if(item.isFile()){
       qDebug()<<"File:"<<item.filePath();
    }
}

Effect display:

1.7 file filtering

QDir dir(dir.current());
QStringList listters;
listters<<"*.txt"<<"*.exe";//< - here is the fi lt er criteria, which depends on the type of item
dir.setNameFilters(listters);
qDebug()<<dir.entryList(listters,QDir::Files);

2. File operation

2.1,QFile

QFile class provides an interface for reading / writing files. It can be used to read / write text files, binary files and I/0 devices of Qt resources.

Generally, the file name is specified when building the QFile object. Of course, it can also be set by using setFileName(). You can use exists () to check if a file exists and remove () to delete a file.

A file can be operated as follows:

open() open
close()close
flush()Refresh
 File reading and writing can be used read(), readLine(), readAll()and write ()
size()Function to get the size of the file
seek()To navigate to any location in the file
pos()To get the current location
atEnd()To determine whether the end of the file has been reached

You can also use the following learned FILE and fstream to operate files.

2.2. Open and write files

File operation flow open > write / read > close

Before accessing a device, you need to use the open() function to open the device, and you must specify the correct opening mode. Different opening modes can be used simultaneously with the "|" symbol.

After the device is turned on, you can use write() or putChar() to write, use the seek function to move the file pointer (if any), use read(), readLine() or readAll() to read, and finally use close() to close the device.

Demo:

    QFile file("demonstration.txt");
    if (!file.open(QIODevice::WriteOnly | QIODevice::Text)) //If the file does not exist, the file will be created
    {
        qDebug() << file.errorString();
    }
    else
    {
        qDebug() << "Open successfully!";
    }
    file.write("ABBA ABBA ABBA");
    file.close();

2.3. Read all contents

QFile file("demonstration.txt");
if (!file.open(QIODevice::ReadOnly | QIODevice::Text)) //If the file does not exist, the file will be created
{
    qDebug() << file.errorString();
}
else
{
    qDebug() << "Open successfully!";
}
while(!file.atEnd())
{
    QByteArray line=file.readLine();
    qDebug()<<line;
}
file.close();

2.4. QIOdevice class

QIODevice class is the basic class of all I/O devices in Qt. It provides an abstract interface for QFIle and other classes

The inheritance diagram is as follows:

2, Standard dialog box

1. Standard input dialog box

#include <QInputDialog>
bool ok;
There are the following:
//Numbers in spinxbox
int i= QInputDialog::getInt(this,"Tips"," Get number",
                            15,//Default value
                            0,//minimum value
                            100,//Maximum
                            1,//step
                            &ok);//Used to determine if ok is clicked

//Number in spinxbox (decimal)
int i= QInputDialog::getDouble(this,"Tips"," Get number",
                               15.34,//Default value
                               0,//minimum value
                               100,//Maximum
                               3,//Display decimal places
                               &ok);//Used to determine if ok is clicked

QStringList items;
//Displays the string in the QStringList
items<<"String 1"<<"String 2"<<"String 3"<<"String 4"<<"String 5";
bool ok;
QString item=QInputDialog::getItem(this,"Tips","Get string",
                                   items,//QStringList type
                                   0,//Selected by default
                                   true,//Can the content be changed
                                   &ok);

//Get the input string, one line
QString text=QInputDialog::getText(this,"Tips","Input string",
                                   QLineEdit::Normal,"Default display content",&ok);

//Get the input string, multiple lines
QString text=QInputDialog::getMultiLineText(this,"Tips","Enter multiline string","Default display content",&ok);

2. Standard font dialog box

#include <QColorDialog>
QColor color=QColorDialog::getColor(Qt::red,//Default selection color
                                    this,"get colors");
if(color.isValid())
{
    ui->lineEdit_4->setText(color.name());
    QPalette pa=ui->lineEdit_4->palette(); //Get palette of lineEdit
    pa.setColor(QPalette::Base,color); //Set to get color
    ui->lineEdit_4->setPalette(pa); //Override settings back
}

3. Standard color dialog box

#include <QFontDialog>
bool ok;
QFont font=QFontDialog::getFont(&ok,
                                QFont("Blackbody")//default font
                                ,this,"Select font");
if(ok)
{
    ui->lineEdit_5->setText(font.key());//Font name
    ui->lineEdit_5->setFont(font); //Set font
}

4. Standard file dialog box

#include <QFileDialog>
QString path=QFileDialog::getExistingDirectory(this,"Select file",
                                               "D:\\");//Starting path
//Select only a single file
QString fileName=QFileDialog::getOpenFileName(this,"Select file","D:\\",//Starting path
                                              "All Files (*);;Text Files(*.txt)");//Screening conditions
//Path to open multiple files
QStringList fileName=QFileDialog::getOpenFileNames(this,"Select file","D:\\",
                                                   "All Files (*);;Text Files (*.txt)");

//It is used to save files, but it will not create files. You need to create files and write contents through file operation
QString fileName=QFileDialog::getSaveFileName(this,"Save file","D:\\",
                                              "All Files (*);;Text Files (*.txt)");

5. Standard message dialog box

QMessageBox::information(this," title","text");
QMessageBox::warning(this,"title","text");
QMessageBox::critical(this,"title","text");
QMessageBox::question(this,"title","text");
The return value is the selected button. Of course, the buttons specified by the 4th, 5th and 6th counselors have default values, which can be left blank. Note that this is the first parent class
 The parent class in must be a window object and cannot die before the window is processed,The buttons can be the following:
QMessageBox::NoButton
QMessageBox::Ok
QMessageBox::Cancel
QMessageBox::Yes
QMessageBox::No
QMessageBox::Abort
QMessageBox::Retry
QMessageBox::Ignore
QMessageBox::YesAll
QMessageBox::NoAll

Keywords: Qt

Added by Noctagon on Sat, 15 Jan 2022 03:26:44 +0200

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