QSettings 用法（一）

        本文先从概念和用法上讲述下QSettings的简单用法，最后以一个简单而较全面的使用例子结束，一句话：实践出真知！

QSettings 类提供“持久性”，平台独立的应用程序设置。意思是，程序关闭后QSettings把窗体大小，位置，用户设置的Option 保存起来，下次

打开程序时再重新加载。

如果你需要的是“非持久性” 基于内存的数据结构，可以考虑使用QMap<QString,QVariant> 代替。

通常，对于Windows，配置信息保存在“注册表”中，Mac OS 是XML 文件，Unix 是INI 文件

// 构造函数
QSettings settings("MySoft", "Star Runner"); //  公司或组织名  // 应用程序名

QCoreApplication::setOrganizationName("MySoft");
QCoreApplication::setOrganizationDomain("mysoft.com"); // 专为Mac OS X 准备的
QCoreApplication::setApplicationName("Star Runner");
...
QSettings settings;

如果要在程序很多地方使用QSettings，用 QCoreApplication::setOrganizationName() 和QCoreApplication::setApplicationName() 然后用QSettings 的默认构造函数。

这样，公司或组织名，应用程序名只要指定一次，QSettings settings 到处扔就行。

QSettings 存储了一对键值（ Key / value ） ，Key 是一个QString，Value是一个QVariant

settings.setValue("editor/wrapMargin", 68);  //添加一对键值

添加键值的时侯，如果Key 已存在，则Value 被重写。

出于效率的原因，setValue 不会立既写入（如注册表，INI, XML）, 要立既写入可以用sync() 函数。

int margin = settings.value("editor/wrapMargin").toInt();

通过Key，取回Value。如果指定的Key 不存在，QSettings 返回空的QVariant（转成整型是 0）。

// 类型转换
QSettings settings("MySoft", "Star Runner");
QColor color =settings.value("DataPump/bgcolor").value<QColor>();

// 通过"/" 分组
settings.setValue("mainwindow/size",win->size());
settings.setValue("mainwindow/fullScreen",win->isFullScreen());
settings.setValue("outputpanel/visible",panel->isVisible());

settings.beginGroup("mainwindow");
settings.setValue("size", win->size());
settings.setValue("fullScreen",win->isFullScreen());
settings.endGroup();

settings.beginGroup("outputpanel");
settings.endGroup();

添加分组，并链表化，读写分组

void QSettings::beginWriteArray(constQString& prefix,intsize =-1)

Adds prefix to the current group and starts writing an array of size size. 

If size is -1 (the default), it is automatically determined based on the indexes of the entries written.

If you have many occurrences of a certain set of keys, 

you can use arrays to make your life easier.

For example, let's suppose that you want to save a variable-length list of user names and passwords.

You could then write:

struct Login{

    QString userName;

    QString password;

};

QList<Login> logins;

...

QSettings settings;

settings.beginWriteArray("logins");

for (int i = 0; i < logins.size(); ++i) {

    settings.setArrayIndex(i);

    settings.setValue("userName", list.at(i).userName);

    settings.setValue("password", list.at(i).password);

}

settings.endArray();

遍历分组

int QSettings::beginReadArray(constQString&prefix)

Adds prefix to the current group and starts reading from an array. Returns the size of the array.

Example:

 struct Login {

     QString userName;

     QString password;

 };

 QList<Login> logins;

 ...

 QSettings settings;

 int size = settings.beginReadArray("logins");

 for (int i = 0; i < size; ++i) {

     settings.setArrayIndex(i);

     Login login;

     login.userName = settings.value("userName").toString();

     login.password = settings.value("password").toString();

     logins.append(login);

 }

 settings.endArray();

QStringList QSettings::childGroups()const

Returns a list of all key top-level groups that contain keys that can be read using the QSettings object.

Example:

 QSettings settings;

 settings.setValue("fridge/color", Qt::white);

 settings.setValue("fridge/size", QSize(32, 96));

 settings.setValue("sofa", true);

 settings.setValue("tv", false);

 QStringList groups = settings.childGroups();

 // groups: ["fridge"]

If a groupisset usingbeginGroup(),thefirst-levelkeysin that group are returned,withoutthegroup prefix.

 settings.beginGroup("fridge");

 groups = settings.childGroups();

 // groups: []

You can navigate through the entire setting hierarchy using childKeys() and childGroups() recursively.

See also childKeys() and allKeys().

//  readSettings()  /writeSettings()

 void MainWindow::writeSettings()

 {

    QSettings settings("Moose Soft", "Clipper");

    settings.beginGroup("MainWindow");

    settings.setValue("size", size());

    settings.setValue("pos", pos());

    settings.endGroup();

 }

 void MainWindow::readSettings()

 {

    QSettings settings("Moose Soft", "Clipper");

    settings.beginGroup("MainWindow");

    resize(settings.value("size", QSize(400, 400)).toSize());

    move(settings.value("pos", QPoint(200, 200)).toPoint());

    settings.endGroup();

 }

// readSettings() and writeSettings() 必须分别位于主窗体的构造函数和closeEvent函数里面。

 MainWindow::MainWindow()

 {

    ...

    readSettings();

 }

 void MainWindow::closeEvent(QCloseEvent*event)

 {

    if (userReallyWantsToQuit()) {

        writeSettings();

        event->accept();

    } else {

        event->ignore();

    }

 }

简单用例

main.cpp

#include <QtGui/QApplication>

#include "mainwindow.h"

int main(int argc, char *argv[])

{

    QApplication a(argc, argv);

    MainWindow w;

    w.show();

    return a.exec();

}

mainwindow.h

#ifndef MAINWINDOW_H

#define MAINWINDOW_H

#include <QMainWindow>

namespace Ui {

class MainWindow;

}

class MainWindow : public QMainWindow

{

    Q_OBJECT

public:

    explicit MainWindow(QWidget *parent = 0);

    ~MainWindow();

private:

    Ui::MainWindow *ui;

};

#endif // MAINWINDOW_H

mainwindow.cpp

#include "mainwindow.h"

#include "ui_mainwindow.h"

#include<QList>

#include<QSettings>

#include<QFile>

#include<QStringList>

#include<QDebug>

struct Login {

     QString userName;

     QString password;

 };

MainWindow::MainWindow(QWidget *parent) :

    QMainWindow(parent),

    ui(new Ui::MainWindow)

{

    ui->setupUi(this);

    QList<Login> logins;

    Login lg1[5];

    for(int i=0;i<5;i++){

        lg1[i].userName=QString("log%1").arg(i);

        lg1[i].password="000";

        logins<<lg1[i];

    }

    QString myfile="test.ini";

    QSettings *settings=new QSettings(myfile,QSettings::IniFormat);

    settings->beginWriteArray("logins1");//写数组logins1

    for (int i = 0; i < logins.size(); ++i) {

        settings->setArrayIndex(i);

        settings->setValue("userName", logins.at(i).userName);

        settings->setValue("password", logins.at(i).password);

    }

    QList<Login> logins2;

    Login lg2[5];

    for(int i=0;i<5;i++){

        lg2[i].userName=QString("log%1").arg(i+5);

        lg2[i].password="000";

        logins2<<lg2[i];

    }
      settings->endArray();

    //QString myfile="test.txt";

    //QSettings *settings=new QSettings(myfile,QSettings::IniFormat);

    settings->beginWriteArray("logins2");
//写数组logins2

    for (int i = 5; i < logins2.size()+5; ++i) {

        settings->setArrayIndex(i);

        settings->setValue("userName", logins2.at(i-5).userName);

        settings->setValue("password", logins2.at(i-5).password);

    }

     settings->endArray();

      QStringList groups = settings->childGroups();

      foreach(QString str,groups)//列出所有子组

      qDebug()<<str;

        //QSettings

      int size = settings->beginReadArray("logins1");

      for (int i = 0; i < size; ++i) {

          settings->setArrayIndex(i);

          Login login;

          login.userName = settings->value("userName").toString();

          login.password = settings->value("password").toString();

          logins.append(login);

      }

      settings->endArray();

      qDebug()<<logins.size();

      for(int i=0;i<logins.size();i++)

      {

          qDebug()<<i<<logins[i].userName;

      }

      size = settings->beginReadArray("logins2");

      for (int i = 0; i < size; ++i) {

          settings->setArrayIndex(i);

          Login login;

          login.userName = settings->value("userName").toString();

          login.password = settings->value("password").toString();

          logins.append(login);

      }

      settings->endArray();

      qDebug()<<logins.size();

      for(int i=0;i<logins.size();i++)

      {

          qDebug()<<i<<logins[i].userName;

      }

      settings->beginWriteArray("maingroup");

      //for (int i = 5; i < logins2.size()+5; ++i) {

      settings->setValue("userName", "root");

      settings->setValue("password", "000");

      //}

       settings->endArray();

       qDebug()<<settings->value("maingroup/userName").toString();//列出maingroup下userName的值

}

MainWindow::~MainWindow()

{

    delete ui;

}