Flutter real-time dynamic UI refresh, data interaction

Introduction to setState()

The function of setState() is to mark that the State in StatefulWidget has changed, and the UI needs to be rebuilt. That is, let the Flutter architecture automatically refresh the UI in real time.
When the State of StatefulWidget changes, call setState() to notify the Flutter framework. After receiving the notification, the Flutter framework will re-call the build() method of StatefulWidget to build the UI.

example

To give a simple example:

class Counter extends StatefulWidget {
    
    
  @override
  State<StatefulWidget> createState() {
    
    
    return _CounterState();
  }
}

class _CounterState extends State<Counter> {
    
    
  int _count = 0;
  
  @override
  Widget build(BuildContext context) {
    
    
    return Text('Count: $_count');
  }
  
  void increment() {
    
    
    setState(() {
    
    
      _count++;
    });
  }
}

Here is a StatefulWidget Counter, which maintains a state _count. When we call the increment() method, we call setState() to notify the Flutter framework that _count has changed, and the Flutter framework will call the build() method again to build the UI and update the content of Text.
So the main function of setState() is to notify the Flutter framework to rebuild the UI to update the interface when the state of the StatefulWidget changes.
By using the setState() function, the state can be managed and updated in a stateful widget to achieve dynamic UI interaction and data update.

detailed introduction

1. Function: The setState() function is used to notify the Flutter framework that the state of the widget has changed and request to rebuild the UI. It triggers the widget's build() method, causing the widget to re-render to reflect the latest state.

2. How to use: The setState() function is a method of the State class. Where the state needs to be updated, the code block can be wrapped by calling setState(() { ... }). Inside the code block, you can modify the state.

3. Asynchronous operation: The setState() function is an asynchronous operation, which will add the state update request to Flutter's event queue, and then continue to execute subsequent codes. Once the build for the current frame is complete, the Flutter framework calls the build() method to rebuild the widget.

4. Update scope: The setState() function will only update the widget that called it and its subtree. Therefore, in order to update the state of the entire application, it is usually necessary to use the setState() function on the upper level of the root widget.

5. Immutability: The Flutter framework determines whether a widget needs to be rebuilt by comparing the two state objects before and after. Therefore, when using the setState() function, you should ensure that the updated state object is a new immutable object, rather than modifying the existing object in-place.

6. State management: The setState() function is usually used with StatefulWidget to manage stateful widgets. By calling the setState() function to update the state, the reconstruction of the widget can be triggered, so as to achieve the effect of updating the UI according to the change of the state.