Live Cell Widgets

Besides the core cell functionality, this package comes with a live_cells_ui library which provides a collection of widgets that extend the stock Flutter widgets with functionality which allows their properties to be observed and controlled by cells.

tip

The name of a Live Cells equivalent of a Flutter widget is Live followed by the name of the widget class.

When a cell is given as a parameter for a widget property, the property is said to be bound to the cell. This means that when the value of the cell changes, the value of the property is automatically updated to reflect the value of the cell. Similarly, when the value of the property changes due to user interaction, the value of the cell is updated to reflect the state of the widget.

For example the LiveSwitch widget is a Switch which takes a cell for its value.

LiveSwitch example

CellWidget.builder((c) {
    final state = MutableCell(false);
    
    return Column(
        children: [
            Text(state() ? 'On' : 'Off'),
            LiveSwitch(
                value: state
            ),
            ElevatedButton(
                child: Text('Reset'),
                onPressed: () => state.value = false
            )
        ]
    );
});

In this example:

1. A LiveSwitch is created with its value property bound to the cell state.

2. The initial value of the state cell is false hence the switch is initially in the off position.

3. The state of the switch, initially "Off" is displayed in a Text widget above the switch.

4. When the switch is turned to on by the user, the value of the state cell is updated to true and "On" is displayed in the Text widget.

5. Likewise, when the switch is turned off the value of the state cell is updated to false and "Off" is displayed in the Text widget.

The "Reset" button below the switch sets the value of the state cell to false, which results in the switch widget resetting to the off position and "Off" being displayed.

Notice that user input was handled entirely in a declarative manner. There was no need to provide an onChanged callback, nor any need to call setState.

Text Fields

LiveTextField is another widget provided by this library that allows user input to be observed and handled using cells. Unlike TextField which takes a TextEditingController, LiveTextField takes a content cell which is bound to the content of the field. It also takes an optional selection cell which is bound to the selection.

The content cell can be used both to observe and set the content of the field. Here's a simple example that echoes whatever is written in the field to a Text widget.

LiveTextField example

CellWidget.builder((c) {
    final content = MutableCell('');
    
    return Column(
        children: [
            Text(content()),
            LiveTextField(
                content: content
            ),
            ElevatedButton(
                child: Text('Clear'),
                onPressed: () => content.value = ''
            )
        ]
    );
});

Like the LiveSwitch example, we didn't need an onChanged callback nor did we need to add a listener to a TextEditingController object. The "Clear" button clears the content of the text field by setting the value of the content cell to the empty string.

caution

If you provide a cell for the selection property of LiveTextField, it has to be reset as well as the content cell when clearing the text field.