QSqlRelationalTableModel显示图标而不是数据

Question

我正在显示一个包含一个blob列(pdf文件)的表。我本来可以为用户隐藏该列，但是我想在列中显示一个图标，当它是一个文件时。我子类化了QsqlRealtionalTableModel并重载了数据函数。如下所示。我的问题是，现在图标与PDF中的混淆数据一起显示。我认为这个重载函数正在取代数据的图标。

QVariant RelationalTableModelWithIcon::data(const QModelIndex &item, int role) const
{
  if(item.column() == 3 && role == Qt::DecorationRole)
    {
      QSqlRecord r= record(item.row());
      QByteArray a= r.field(3).value().toByteArray();
      QIcon icon = QIcon(":/icons/Art/Icons/Iynque-Flat-Ios7-Style-Documents-Pdf.ico");
      if(a.isNull() == false)
        {
          return QVariant(icon);
        }
    }
  return QSqlRelationalTableModel::data(item,role);
}

DROP TABLE IF EXISTS `ComOper`.`documentsqueue` ;

CREATE TABLE IF NOT EXISTS `ComOper`.`documentsqueue` (
  `iddocumentsqueue` INT NOT NULL AUTO_INCREMENT,
  `iddocument` INT NULL DEFAULT 1,
  `name` VARCHAR(45) NOT NULL,
  `image` MEDIUMBLOB NULL,
  `dateEntered` DATE NULL,
  `dateExpired` DATE NULL,
  `dateApproved` DATE NULL,
  `notes` MEDIUMTEXT NULL,
  `archived` TINYINT NULL DEFAULT 0,
  `iddocType` INT NOT NULL DEFAULT 1,
  `idsupplier` INT NOT NULL,
  `idfacilities` INT NOT NULL DEFAULT 1,
  `idproducts` INT NOT NULL DEFAULT 1,
  `iduser` INT NOT NULL DEFAULT 1,
  PRIMARY KEY (`iddocumentsqueue`),
  CONSTRAINT `fk_documentsqueue_docType1`
    FOREIGN KEY (`iddocType`)
    REFERENCES `ComOper`.`docType` (`iddocType`)
    ON DELETE NO ACTION
    ON UPDATE NO ACTION,
  CONSTRAINT `fk_documentsqueue_documents1`
    FOREIGN KEY (`iddocument`)
    REFERENCES `ComOper`.`documents` (`iddocument`)
    ON DELETE NO ACTION
    ON UPDATE NO ACTION,
  CONSTRAINT `fk_documentsqueue_user1`
    FOREIGN KEY (`iduser`)
    REFERENCES `ComOper`.`user` (`iduser`)
    ON DELETE NO ACTION
    ON UPDATE NO ACTION,
  CONSTRAINT `fk_documentsqueue_products1`
    FOREIGN KEY (`idproducts`)
    REFERENCES `ComOper`.`products` (`idproducts`)
    ON DELETE NO ACTION
    ON UPDATE NO ACTION,
  CONSTRAINT `fk_documentsqueue_facilities1`
    FOREIGN KEY (`idfacilities`)
    REFERENCES `ComOper`.`facilities` (`idfacilities`)
    ON DELETE NO ACTION
    ON UPDATE NO ACTION,
  CONSTRAINT `fk_documentsqueue_supplier1`
    FOREIGN KEY (`idsupplier`)
    REFERENCES `ComOper`.`supplier` (`idsupplier`)
    ON DELETE NO ACTION
    ON UPDATE NO ACTION)

Answer 1

为了避免显示不可读的PDF文本，您必须在他们请求Qt::DisplayRole角色时返回一个空字符串，当他们请求Qt::DecorationRole角色时返回图标。我还建议只在图标唯一的情况下阅读一次，如下所示：

*.h

private:
    QIcon icon;

*.cpp

RelationalTableModelWithIcon::RelationalTableModelWithIcon(QObject *parent, QSqlDatabase db):
    QSqlRelationalTableModel(parent, db)
{
    icon =  QIcon(":/icons/Art/Icons/Iynque-Flat-Ios7-Style-Documents-Pdf.ico");
}
QVariant RelationalTableModelWithIcon::data(const QModelIndex &index, int role) const
{
    if(index.column() == 3){
        if(role == Qt::DisplayRole)
            return "";
        else if ( role == Qt::DecorationRole)
            return icon;
    }
    return QSqlRelationalTableModel::data(index, role);
}