谁能给我解释一下下面的块定义函数

leonn123

谁能给我解释一下下面的块定义函数,特别是为什么要作一个属性常量,一个属性非常量,两个块?有什么区别?
void
defineBlockWithAttributes(
    AcDbObjectId& blockId, // This is a returned value.
    const AcGePoint3d& basePoint,
    double textHeight,
    double textAngle)
{
    int retCode = 0;
    AcDbBlockTable *pBlockTable = NULL;
    AcDbBlockTableRecord* pBlockRecord
       = new AcDbBlockTableRecord;
    AcDbObjectId entityId;

    // Step 1: Set the block name and base point of the block definition
    //
    pBlockRecord->setName("ASDK-BLOCK-WITH-ATTR");
    pBlockRecord->setOrigin(basePoint);

    // Open the block table for write.
    //
    acdbHostApplicationServices()->workingDatabase()
        ->getSymbolTable(pBlockTable, AcDb::kForWrite);

    // Step 2: Add the block table record to block table.
    //
    pBlockTable->add(blockId, pBlockRecord);

    // Step 3: Create a circle entity.
    //
    AcDbCircle *pCircle = new AcDbCircle;
    pCircle->setCenter(basePoint);
    pCircle->setRadius(textHeight * 4.0);
    pCircle->setColorIndex(3);

    // Append the circle entity to the block record.
    //
    pBlockRecord->appendAcDbEntity(entityId, pCircle);
    pCircle->close();

    // Step 4: Create an attribute definition entity.
    //
    AcDbAttributeDefinition *pAttdef
        = new AcDbAttributeDefinition;

    // Set the attribute definition values.
    //
    pAttdef->setPosition(basePoint);
    pAttdef->setHeight(textHeight);
    pAttdef->setRotation(textAngle);
    pAttdef->setHorizontalMode(AcDb::kTextLeft);
    pAttdef->setVerticalMode(AcDb::kTextBase);
    pAttdef->setPrompt("rompt");
    pAttdef->setTextString("DEFAULT");
    pAttdef->setTag("Tag");
    pAttdef->setInvisible(Adesk::kFalse);
    pAttdef->setVerifiable(Adesk::kFalse);
    pAttdef->setPreset(Adesk::kFalse);
    pAttdef->setConstant(Adesk::kFalse);
    pAttdef->setFieldLength(25);

    // Append the attribute definition to the block.
    //
    pBlockRecord->appendAcDbEntity(entityId, pAttdef);

    // The second attribute definition is a little easier
    // because we are cloning the first one.
    //
    AcDbAttributeDefinition *pAttdef2
        = AcDbAttributeDefinition::cast(pAttdef->clone());

    // Set the values which are specific to the
    // second attribute definition.
    //
    AcGePoint3d tempPt(basePoint);
    tempPt.y -= pAttdef2->height();
    pAttdef2->setPosition(tempPt);
    pAttdef2->setColorIndex(1); // Red
    pAttdef2->setConstant(Adesk::kTrue);

    // Append the second attribute definition to the block.
    //
    pBlockRecord->appendAcDbEntity(entityId, pAttdef2);

    pAttdef->close();
    pAttdef2->close();
    pBlockRecord->close();
    pBlockTable->close();
    return;
}