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NVDA Objects are the fundamental building blocks that represent controls and GUI elements in NVDA. Every widget, regardless of its underlying API, is represented as an NVDAObject instance.

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What is an NVDA Object?

An NVDA Object provides:
  • Standardized properties: name, role, value, states, description
  • Navigation: parent, children, next, previous relationships
  • Event handling: Response to focus, value changes, etc.
  • Scripting: Custom commands and gesture bindings
  • Text access: Through TextInfo objects
import api

# Get the current focus object
focusObj = api.getFocusObject()

# Access standard properties
name = focusObj.name
role = focusObj.role
value = focusObj.value
states = focusObj.states
description = focusObj.description

# Get location on screen
location = focusObj.location  # (left, top, width, height)

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Base Class: NVDAObject

The NVDAObject class is defined in source/NVDAObjects/__init__.py:
NVDAObject base class
class NVDAObject(
    documentBase.TextContainerObject,
    baseObject.ScriptableObject,
    metaclass=DynamicNVDAObjectType,
):
    """NVDA's representation of a single control/widget.
    
    Every widget, regardless of how it is exposed by an application or 
    the operating system, is represented as a single NVDAObject instance.
    """
    
    cachePropertiesByDefault = True
    TextInfo = NVDAObjectTextInfo
    
    # Core properties implemented via auto-property pattern
    def _get_name(self) -> str:
        """The label or name of this object"""
        return ""
    
    def _get_role(self) -> controlTypes.Role:
        """The role or type of control"""
        return controlTypes.Role.UNKNOWN
    
    def _get_value(self) -> str:
        """The value of the control"""
        return ""
    
    def _get_states(self) -> Set[controlTypes.State]:
        """Set of state constants"""
        return set()

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API Classes

NVDA supports multiple accessibility APIs through specialized classes:

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IAccessible Objects

For MSAA/IAccessible controls:
IAccessible Example
from NVDAObjects.IAccessible import IAccessible

class CustomButton(IAccessible):
    def _get_name(self):
        # Override name from IAccessible
        return self.IAccessibleObject.accName(self.IAccessibleChildID) or "Unnamed"
    
    def _get_role(self):
        return controlTypes.Role.BUTTON

​
UI Automation Objects

For modern Windows UIA controls:
UIA Example
from NVDAObjects.UIA import UIA

class CustomEdit(UIA):
    def _get_value(self):
        # Access UIA properties
        return self.UIAElement.CurrentValue
    
    def _get_states(self):
        states = super()._get_states()
        if self.UIAElement.CurrentIsReadOnly:
            states.add(controlTypes.State.READONLY)
        return states

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Window Objects

For direct Win32 window access:
Window Example
from NVDAObjects.window import Window

class CustomWindow(Window):
    def _get_name(self):
        # Access window properties
        return self.windowText or "Untitled"
    
    @property
    def windowClassName(self):
        return self._windowClassName
    
    @property
    def windowControlID(self):
        return self._windowControlID

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Dynamic Class Creation

One of NVDA’s most powerful features is dynamic class creation. When an object is instantiated:
Dynamic class creation flow
class DynamicNVDAObjectType(baseObject.ScriptableObject.__class__):
    _dynamicClassCache = {}
    
    def __call__(self, chooseBestAPI=True, **kwargs):
        # 1. Find the best API class
        if chooseBestAPI:
            APIClass = self.findBestAPIClass(kwargs)
            if not APIClass:
                return None
        
        # 2. Instantiate the API class
        obj = APIClass.__new__(APIClass, **kwargs)
        obj.__init__(**kwargs)
        
        # 3. Build overlay class list
        clsList = []
        obj.findOverlayClasses(clsList)
        
        # 4. Let app module choose classes
        if obj.appModule:
            obj.appModule.chooseNVDAObjectOverlayClasses(obj, clsList)
        
        # 5. Let global plugins choose classes
        for plugin in globalPluginHandler.runningPlugins:
            plugin.chooseNVDAObjectOverlayClasses(obj, clsList)
        
        # 6. Construct dynamic class
        bases = tuple(optimized_bases)
        name = "Dynamic_" + "_".join([x.__name__ for x in clsList])
        newCls = type(name, bases, {"__module__": __name__})
        
        # 7. Mutate object to new class
        obj.__class__ = newCls
        
        # 8. Initialize overlay classes
        for cls in reversed(newCls.__mro__):
            if hasattr(cls, 'initOverlayClass'):
                cls.initOverlayClass(obj)
        
        return obj
This allows NVDA to combine generic API support with application-specific behaviors without modifying core code.

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Creating Custom NVDA Objects

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Step 1: Define the Class

Inherit from the appropriate base class:
Custom NVDA Object
from NVDAObjects.IAccessible import IAccessible
from scriptHandler import script
import ui
import controlTypes

class EnhancedEditField(IAccessible):
    """Custom edit field with additional functionality"""
    
    def _get_name(self):
        # Customize the name
        return f"Enhanced: {super().name}"
    
    def _get_description(self):
        # Add helpful description
        return f"Length: {len(self.value)} characters"
    
    @script(gesture="kb:NVDA+l")
    def script_reportLength(self, gesture):
        """Report the length of text in this field"""
        length = len(self.value) if self.value else 0
        ui.message(f"{length} characters")
    
    def initOverlayClass(self):
        """Called when this overlay is applied to an object"""
        # Perform initialization
        pass

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Step 2: Choose When to Use It

In your app module or global plugin:
Choosing overlay classes
import appModuleHandler
from NVDAObjects.IAccessible import IAccessible
import controlTypes

class AppModule(appModuleHandler.AppModule):
    
    def chooseNVDAObjectOverlayClasses(self, obj, clsList):
        """Choose custom classes for objects in this app"""
        # Check if this is an edit field we want to enhance
        if (
            isinstance(obj, IAccessible) and
            obj.role == controlTypes.Role.EDITABLETEXT and
            obj.windowClassName == "Edit"
        ):
            # Insert our custom class at the beginning
            clsList.insert(0, EnhancedEditField)
Insert custom classes at index 0 so they are resolved first in the method resolution order (MRO).

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Common Properties

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Essential Properties

Essential properties
class MyObject(NVDAObject):
    def _get_name(self) -> str:
        """Label of the control (e.g., button text)"""
        return "OK"
    
    def _get_role(self) -> controlTypes.Role:
        """Type of control"""
        return controlTypes.Role.BUTTON
    
    def _get_value(self) -> str:
        """Current value (e.g., slider position, checkbox state)"""
        return "50%"
    
    def _get_states(self) -> Set[controlTypes.State]:
        """Set of states"""
        states = set()
        states.add(controlTypes.State.FOCUSABLE)
        states.add(controlTypes.State.FOCUSED)
        return states
    
    def _get_description(self) -> str:
        """Description (usually from tooltip)"""
        return "Click to confirm"

​
Location and Visibility

Location properties
    def _get_location(self) -> Tuple[int, int, int, int]:
        """Screen coordinates (left, top, width, height)"""
        return (100, 100, 200, 50)
    
    def _get_hasIrrelevantLocation(self) -> bool:
        """True if object is offscreen or invisible"""
        return False
    
    def _get_presentationType(self):
        """How this object should be presented"""
        return self.presType_content  # or presType_layout
Navigation properties
    def _get_parent(self) -> Optional['NVDAObject']:
        """Parent object in hierarchy"""
        return self._parent
    
    def _get_firstChild(self) -> Optional['NVDAObject']:
        """First child object"""
        return self._firstChild
    
    def _get_lastChild(self) -> Optional['NVDAObject']:
        """Last child object"""
        return self._lastChild
    
    def _get_next(self) -> Optional['NVDAObject']:
        """Next sibling"""
        return self._next
    
    def _get_previous(self) -> Optional['NVDAObject']:
        """Previous sibling"""
        return self._previous
    
    def _get_children(self) -> List['NVDAObject']:
        """List of all direct children"""
        return []

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Working with States

States indicate the current condition of a control:
Using states
import controlTypes

def processObject(obj):
    states = obj.states
    
    # Check for specific states
    if controlTypes.State.FOCUSED in states:
        print("Object has focus")
    
    if controlTypes.State.CHECKED in states:
        print("Checkbox is checked")
    
    if controlTypes.State.EXPANDED in states:
        print("Tree item is expanded")
    
    # Common states
    # FOCUSABLE, FOCUSED, SELECTED, SELECTABLE
    # CHECKED, CHECKABLE, PRESSED, EXPANDED, COLLAPSED
    # READONLY, DISABLED, INVISIBLE, OFFSCREEN
    # BUSY, LINKED, VISITED, PROTECTED

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Text Access

NVDA Objects can provide text access:
Text access
# Get a TextInfo object
textInfo = obj.makeTextInfo(textInfos.POSITION_FIRST)

# Move and read text
textInfo.expand(textInfos.UNIT_LINE)
line_text = textInfo.text

# Get all text
storyInfo = obj.makeTextInfo(textInfos.POSITION_ALL)
all_text = storyInfo.text

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Custom TextInfo

Custom TextInfo
from textInfos import TextInfo

class CustomTextInfo(TextInfo):
    def _getStoryText(self):
        """Return all text"""
        return self.obj.value or ""
    
    def _getStoryLength(self):
        """Return text length"""
        return len(self._getStoryText())

class MyObject(NVDAObject):
    TextInfo = CustomTextInfo

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Focus Redirect

Redirect focus to a different object:
Focus redirect
class ContainerObject(NVDAObject):
    def _get_focusRedirect(self):
        """When this object receives focus, redirect to its first child"""
        return self.firstChild

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Tree Interceptors

Complex documents can have tree interceptors (like browse mode):
Tree interceptor
from browseMode import BrowseModeTreeInterceptor

class MyDocument(NVDAObject):
    def _get_treeInterceptorClass(self):
        """Specify tree interceptor class"""
        return BrowseModeTreeInterceptor
    
    shouldCreateTreeInterceptor = True

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Practical Example: Custom Button

Complete example of a custom button with enhanced features:
Complete custom button example
from NVDAObjects.IAccessible import IAccessible
from scriptHandler import script
import ui
import tones
import controlTypes

class EnhancedButton(IAccessible):
    """A button with sound effects and additional info"""
    
    def _get_name(self):
        # Add emoji to name for fun
        base_name = super().name
        return f"🔘 {base_name}"
    
    def _get_description(self):
        # Provide helpful description
        return f"Press {self.name} button to activate"
    
    def event_gainFocus(self):
        """Play sound when button receives focus"""
        tones.beep(440, 50)
        super().event_gainFocus()
    
    @script(
        gesture="kb:NVDA+b",
        description="Report button information"
    )
    def script_reportInfo(self, gesture):
        """Report detailed button information"""
        info = [
            f"Name: {self.name}",
            f"Role: {self.role}",
            f"Location: {self.location}",
            f"Window class: {self.windowClassName}",
        ]
        ui.message(", ".join(info))
    
    def initOverlayClass(self):
        """Initialize the button"""
        # Log when this overlay is applied
        log.debug(f"Enhanced button overlay applied to {self.name}")

# In app module:
class AppModule(appModuleHandler.AppModule):
    def chooseNVDAObjectOverlayClasses(self, obj, clsList):
        if obj.role == controlTypes.Role.BUTTON:
            clsList.insert(0, EnhancedButton)

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Best Practices

Properties are cached by default for performance. To disable caching for a specific property:
class MyObject(NVDAObject):
    _cache_dynamicProperty = False
    
    def _get_dynamicProperty(self):
        # This will be fetched every time
        return self._getCurrentValue()
Classes in clsList should be ordered from most specific to most general:
def chooseNVDAObjectOverlayClasses(self, obj, clsList):
    # Most specific first
    clsList.insert(0, VerySpecificClass)
    # More general after
    clsList.append(GeneralClass)
NVDA uses weak references for object relationships. Don’t store strong references unnecessarily:
# Good - uses weak reference
self._parentRef = weakref.ref(parent)

# Bad - strong reference creates memory leak
self._parent = parent
Only access API-specific properties when you know the object type:
from NVDAObjects.IAccessible import IAccessible

if isinstance(obj, IAccessible):
    accName = obj.IAccessibleObject.accName(obj.IAccessibleChildID)

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See Also

Events

Learn about event handling

Scripts & Gestures

Add commands to objects

Writing Plugins

Create app modules and overlays

Architecture Overview

Understand the big picture

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