# Working with schematics

## The current document

[`ISch_ServerInterface.GetCurrentSchDocument`](https://altiumdeveloper.github.io/ad-sdk-docs/reference/sch/ISch_ServerInterface.md#getcurrentschdocument) returns
the active schematic document, or `null` when the active document is not a schematic. Schematic sheets are
[`ISch_Sheet`](https://altiumdeveloper.github.io/ad-sdk-docs/reference/sch/ISch_Sheet.md) and schematic libraries [`ISch_Lib`](https://altiumdeveloper.github.io/ad-sdk-docs/reference/sch/ISch_Lib.md);
both are [`ISch_Document`](https://altiumdeveloper.github.io/ad-sdk-docs/reference/sch/ISch_Document.md):

```csharp
ISch_ServerInterface schServer = SCH.GlobalVars.SchServer;
if (schServer == null)
    return;

ISch_Document document = schServer.GetCurrentSchDocument();
if (document == null)
    return;

ISch_Lib library = document as ISch_Lib; // null on a schematic sheet
```

## Iterating over objects

An [`ISch_Iterator`](https://altiumdeveloper.github.io/ad-sdk-docs/reference/sch/ISch_Iterator.md) walks the objects of a document or of a container such as a
component. Restrict it to some object kinds with a filter, then step through the objects:

```csharp
ISch_Iterator iterator = document.SchIterator_Create();
var objectSet = new SCH.TObjectSet();
objectSet.Add(SCH.TObjectId.eWire);
iterator.AddFilter_ObjectSet(objectSet);

for (var wire = iterator.FirstSchObject() as ISch_Wire; wire != null; wire = iterator.NextSchObject() as ISch_Wire)
{
    // ...
}

document.SchIterator_Destroy(ref iterator);
```

## Changing objects

Tell the schematic editor before and after changing an object, so that undo and the other editor sub-systems stay
consistent. The notifications go through the [`ISch_RobotManager`](https://altiumdeveloper.github.io/ad-sdk-docs/reference/sch/ISch_RobotManager.md):

```csharp
ISch_RobotManager robot = schServer.GetState_RobotManager();

robot.SendMessage(wire, null, SCH.SCHConstant.SCHMBeginModify, SCH.SCHConstant.NoEventData);
wire.SetState_Color(0x0000C8);
robot.SendMessage(wire, null, SCH.SCHConstant.SCHMEndModify, SCH.SCHConstant.NoEventData);

wire.GraphicallyInvalidate();
```

`GraphicallyInvalidate` redraws the object.

## Creating objects

[`ISch_ServerInterface.SchObjectFactory`](https://altiumdeveloper.github.io/ad-sdk-docs/reference/sch/ISch_ServerInterface.md#schobjectfactory) creates a design
object of a [`TObjectId`](https://altiumdeveloper.github.io/ad-sdk-docs/reference/sch/TObjectId.md) kind. Position it, then add it to its owner: a document, or
a component for pins and graphical primitives.

```csharp
ISch_Lib library = schServer.GetCurrentSchDocument() as ISch_Lib;

var component = schServer.SchObjectFactory(SCH.TObjectId.eSchComponent, SCH.TObjectCreationMode.eCreate_Default) as ISch_Component;
component.MoveToXY(0, 0);
library.AddSchComponent(component);

var pin = schServer.SchObjectFactory(SCH.TObjectId.ePin, SCH.TObjectCreationMode.eCreate_GlobalCopy) as ISch_Pin;
pin.MoveToXY(0, 0);
pin.SetState_OwnerPartId(component.GetState_CurrentPartID());
pin.SetState_OwnerPartDisplayMode(component.GetState_DisplayMode());
component.AddSchObject(pin);

library.SetState_Current_SchComponent(component);
library.GraphicallyInvalidate();
```