Article directory
Problem Description
I developed a page using flutter. There are some controls A written by myself on the page. There is a button in control A. When I click the button in control A, I directly call setState in onPressed and find that the page is not refreshed.
onPressed: () {
// 在这里触发页面刷新的逻辑
setState(() {
// 更新页面的状态...
});
}
How to achieve an overall refresh of the page where control A is located?
Solution
In Flutter, to refresh the entire page after clicking the button in control A, you can use the following steps:
Define the callback function in control A
In the code of control A, define a callback function for the button and pass the callback function as a parameter to the button. This callback function is called when the button is clicked.
class WidgetA extends StatelessWidget {
final VoidCallback onPressed;
WidgetA({
required this.onPressed});
Widget build(BuildContext context) {
return Container(
// 控件A的布局和其他代码...
child: RaisedButton(
onPressed: onPressed,
child: Text('按钮'),
),
);
}
}
Use control A in the page
In your page, use control A and pass a callback function to it. This callback function will trigger a refresh of the page.
class YourPage extends StatefulWidget {
_YourPageState createState() => _YourPageState();
}
class _YourPageState extends State<YourPage> {
// 页面的状态和其他代码...
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('Your Page'),
),
body: WidgetA(
onPressed: () {
// 在这里触发页面刷新的逻辑
setState(() {
// 更新页面的状态...
});
},
),
);
}
}
Call setState in the button's callback function: In the button's callback function, notify the Flutter framework that the page needs to be rebuilt by calling setState. This triggers a call to the build method, which refreshes the page.
In this way, when the button in control A is clicked, the callback function passed to control A will be called, and this callback function will trigger a page refresh. Make sure to use the setState method when updating the page state to tell the Flutter framework that the UI needs to be rebuilt.
Cause Analysis
review questions
Why use a callback function for the onPressed key processing of RaisedButton in WidgetA, and call setState in the callback function to refresh the entire page, while directly using setState in the onPressed function of Button in WidgetA will not refresh the entire page? For example: call directly in WidgetA
onPressed: () {
// 在这里触发页面刷新的逻辑
setState(() {
// 更新页面的状态...
});就不会刷新整个页面
Cause Analysis
In Flutter, the purpose of setState is to notify the Flutter framework to rebuild the UI to reflect state changes. setState must be called in the context associated with the UI being built. If you try to call setState directly inside a control rather than in the context associated with that control, it will not trigger a UI refresh.
In this case, WidgetA is a separate control, and setState must be called in the context associated with WidgetA to work properly. If you call setState directly in WidgetA's button callback, it will not cause a refresh of the external page because this setState is not in the context of the page.
By passing the callback function to WidgetA, you are actually deferring the setState call to the page context. This way, when this passed callback function is called in the button callback function in WidgetA, it actually calls setState in the page context, thus triggering a refresh of the page.
In short, setState must be called in a context relevant to the UI build, and passing it from the control to the page via a callback function ensures that the page refresh is triggered in the correct context.
Precautions for using setState
There are some things to keep in mind when using setState for state updates:
contextual correctness
setState must be called in a location associated with the current widget's context. If setState is called in the incorrect context, it will not trigger a refresh of the UI. Typically, you should use setState in a method of the State object, such as a callback in the build method.
setState(() {
// 更新状态...
});
Asynchronous updates
setState does not trigger UI reconstruction immediately, but is scheduled to be executed later in the microtask queue. This means that the code immediately following setState will continue to execute without waiting for the UI rebuild to complete. If you need to perform some operations after the state is updated, you can use mechanisms such as Future or afterLayout plug-ins after setState.
setState(() {
// 更新状态...
});
// 此处的代码会在UI重建完成后执行
Avoid deep nesting
Avoid calling setState in deeply nested callbacks as this may cause performance issues. Try to place setState as high as possible to ensure that only the parts that really need to be updated are rebuilt.
Avoid frequent calls
Avoid calling setState frequently in a short period of time as this may cause performance degradation. If there are multiple states that need to be updated, try combining them into a single setState call to reduce the number of rebuilds.
Avoid calling in build method
Avoid calling setState directly in the build method as this can lead to infinitely recursive builds. If you need to perform some logic at build time, consider using lifecycle methods such as initState or didChangeDependencies.
Avoid calling in dispose method
Avoid calling setState in the dispose method, because during the dispose phase, the widget has been destroyed and can no longer trigger UI reconstruction.
Correct use of setState can ensure that state updates can correctly trigger the reconstruction of the UI, but you need to pay attention to the correctness of the context and some performance considerations.
Conclusion Flutter is an open source UI toolkit developed by Google that allows you to create high-quality, beautiful applications on different platforms without writing a lot of platform-specific code. I will learn and delve into all aspects of Flutter. From basic knowledge to advanced techniques, from UI design to performance optimization, join us to discuss and learn together, and enter the wonderful world of Flutter together!