在Qt5 / Qml中无法写入文件

Question

for my QML project I need a simple IODevice to work with files so I took this one from Nokia Dev But I tweaked it a little, for purposes of my work. Reading from file works like a charm(this proves, that there is no “wrong path to file” problem”), but writing to file is broken, and I can't find a reason why.

Here is the code:

fileio.h

#ifndef FILEIO_H
#define FILEIO_H

#include <QObject>

class FileIO : public QObject
{
    Q_OBJECT

public:
    explicit FileIO(QObject *parent = 0);

    Q_INVOKABLE QString read(const QString& Url);
    Q_INVOKABLE bool write(const QString& Url, QString data);


public slots:

signals:
    void error(const QString& msg);

private:
    QString mSource;
};

#endif // FILEIO_H

fileio.cpp

#include "fileio.h"
#include <QFile>
#include <QTextStream>

FileIO::FileIO(QObject *parent) :
    QObject(parent)
{

}

QString FileIO::read(const QString& Url)
{
    mSource = Url;
    if (mSource.isEmpty()){
        emit error("source is empty");
        return QString();
    }

    QFile file(mSource);
    QString fileContent;
    if ( file.open(QIODevice::ReadOnly) ) {
        QString line;
        QTextStream t( &file );
        t.setCodec("UTF-8");
        do {
            line = t.readLine();
            fileContent += line;
         } while (!line.isNull());

        file.close();
    } else {
        emit error("Unable to open the file");
        return QString();
    }



    return fileContent;
}

bool FileIO::write(const QString& Url, QString data)
{
    mSource = Url;
    if (mSource.isEmpty()){
        emit error("source is empty");
        return false;}

        QFile file(mSource);
        if (!file.open(QIODevice::WriteOnly | QIODevice::Truncate)){
            emit error("Error");
            return false;}

        QTextStream out(&file);
        out << data;
        //emit error("data:" + data); //This one was used to debug, Yet no errors were emmited when Write is called


        file.close();

        return true;
}

I needed my app to load settings from external file (I cant use QSettings, as I wish to give user access these settings by external script or through text editor when app is not launched). So for every setting I have a file with a single Utf-8 string, which is loaded into qml (smth like

property string interfacecolor1 : myFile.read("://settings/color1");

), and it works. But I also want to change settings in qml Example would be:

TextField{
                id:fieldsurname
                Layout.fillWidth: true
                text: myFile.read("://settings/surname"); //Shows user current setting, works perfectly
                onTextChanged: {console.log(fieldsurname.text); //I just check if textfield behaves as supposed, returns what I expect from it.
myFile.write("://settings/surname", fieldsurname.text); //Write text from textfield (it will be for an embeded platform, so I probably need to change setting every new char)
surname = myFile.read("://settings/surname"); //I write new setting to property from new text from file
console.log(myFile.read("://settings/surname")) //Returns an unchanged string
}
            }

Also forgot to mention, that manualy editing files also works, settings are changed accordingly, app behaves as it should.

So the question is: What is wrong?

Ps: this is a duplicate of this question on qt-project but the question got burried, and I need an answer ASAP. Thanks in advance.

Answer 1

Qrc files are read-only. You cannot write to them. You'll have to put the file into the real filesystem and read/write it from/to there.

Answer 2

You can use QSettings to save the settings of your application :

QSettings settings("organizationName","applicationName");
settings.setValue("settings/surname",fieldsurname.text);

Or read them :

surname = settings.value("settings/surname","").toString();

But in case it is necessary to use files(You may want to import settings from other devices using files) You should note that the files in Qt resources are readonly. So you should first copy your file to some location if you want to change it:

QFile dfile("://settings/surname");
if (dfile.exists())
{
     dfile.copy("./surname");
     QFile::setPermissions("./surname",QFile::WriteOwner | QFile::ReadOwner);
}