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# Events
All magicgui widgets emit events when certain properties change. For each event
there is a corresponding signal attribute on the widget that can be connected to
a callback function. For example, a [`PushButton`][magicgui.widgets.PushButton]
emits an event when it is clicked, and all
[`ValueWidget`][magicgui.widgets.bases.ValueWidget] subclasses (like
[`Slider`][magicgui.widgets.Slider] or [`LineEdit`][magicgui.widgets.LineEdit])
emit an event when their value changes.
## Connecting to events
To connect a callback to an event, use the `connect` method of the signal
attribute. The exact signals available on each widget are mostly defined in
the [base classes](api/widgets/bases.md), and are listed on the [API page
for each respective widget](api/widgets/index.md).
For example, to connect a callback to a [`LineEdit`][magicgui.widgets.LineEdit]
widget's `changed` event:
=== "Widget API"
```python
from magicgui import widgets
text = widgets.LineEdit(value='type something')
text.changed.connect(lambda val: print(f"Text changed to: {val}"))
```
=== "`magicgui` decorator"
```python
from magicgui import magicgui
@magicgui
def my_function(text: str):
...
my_function.text.changed.connect(lambda val: print(f"Text changed to: {val}"))
```
=== "`magic_factory` decorator"
```python
from magicgui import magic_factory
def _on_init(widget):
widget.text.changed.connect(lambda val: print(f"Text changed to: {val}"))
@magic_factory(widget_init=_on_init)
def my_function(text: str):
...
my_widget = my_function()
```
!!! info "It's all `psygnal` under the hood"
**magicgui** uses [psygnal](https://psygnal.readthedocs.io/) for its event
system. For greater detail on the `connect` method and its options, see
the [Usage section](https://psygnal.readthedocs.io/en/latest/usage/)
of psygnal's documentation, or the [`psygnal.SignalInstance.connect`][psygnal._signal.SignalInstance.connect] API
reference.
!!! tip
Note that `connect` returns the callable that it was passed, so you can
use it as a decorator if you prefer.
```python
text = widgets.LineEdit(value='type something')
# this works
text.changed.connect(lambda val: print(f"Text changed to: {val}"))
# so does this
@text.changed.connect
def on_text_changed(val):
print(f"Text changed to: {val}")
```
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