Qt生成缩略图片存入sqlite

Qt生成缩略图片存入sqlite

新建一个工程pro文件中加入 QT += sql 添加sql支持。

>folded

// main.cpp

#include <QApplication>
#include <QtGui>
#include <QSqlDatabase>
#include <QSqlError>
#include <QSqlQuery>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    //添加数据库,不表
    QSqlDatabase db = QSqlDatabase::addDatabase("QSQLITE", "conn1");
    db.setDatabaseName("/home/htux/thumbs.sqlite");
    if(!db.open())  return 1;

    QByteArray baImage;

    QString filename = "/home/htux/file2.jpg";
    QPixmap pixmapIn(filename);

    QBuffer buffer(&baImage);
    buffer.open(QIODevice::WriteOnly);

    QPixmap pixmapSmall;
    //让生成的缩略图高宽都不超过256.
    pixmapSmall = pixmapIn.scaled(256,256,
                  Qt::KeepAspectRatio, Qt::SmoothTransformation);
    //保存生成的缩略图到ByteArray, 格式为JPG, 图片质量50.
    //图片质量的取值Qt文档中没查到,不过按照国际惯例应该是0-100
    //保存几个不同质量的图片看看差别
    pixmapSmall.save(&buffer, "JPG",50);
    pixmapSmall.save("/home/htux/file2.png", "PNG");
    pixmapSmall.save("/home/htux/file2-5.jpg", "JPG", 20);
    pixmapSmall.save("/home/htux/file2-5.jpg", "JPG", 50);
    pixmapSmall.save("/home/htux/file2-8.jpg", "JPG", 80);

    QSqlQuery query(db);

    query.exec("CREATE TABLE thumbs "
                "(id INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,"
                " filename VCHAR(20) , thumbnail BLOB);");

    QString sql = QString("INSERT INTO thumbs VALUES "
                "( NULL , :filename, :thumbnail );");

    query.prepare(sql);
    query.bindValue(":filename", filename);
    query.bindValue(":thumbnail", baImage);

    query.exec();

    query.exec("select * from thumbs;");

    //跳到最后存入的记录
    if (!query.last())  return 1;

    QPixmap pixmapOut;
    //读出存入的图片
    pixmapOut.loadFromData(query.value(2).toByteArray());

    db.close();
    //把图片用Label显示出来.
    QLabel label;
    label.setPixmap(pixmapOut);
    label.show();

    return a.exec();
}