Lazy Loading Flutter

Lazy Loading Flutter


Help you to build pull-down refresh and pull-up loading in the simplest way.

Although unprecedented simplicity, but the effect is amazing. It also supports configuration refresh and loading elements. The complete controller allows you to help you control the entire dynamic process.


Lazy Loading Flutter Lazy Loading Flutter Lazy Loading Flutter
Lazy Loading Flutter Lazy Loading Flutter Lazy Loading Flutter

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✨ Features

🛠 Guide

⚙️ Parameter & Interface

🔩 FRefresh param

Param Type Necessary Default desc
child Widget true null Main view content
header Widget false null Elements that will be displayed when you pull down and refresh
headerBuilder HeaderBuilder false null Construct a pull-down refresh element. [Header] configuration will be overwritten.
headerHeight double false 50.0 [header] The height of the area
headerTrigger double false 0.0 The distance to trigger pull-down refresh should be greater than [headerHeight]
onRefresh VoidCallback false null Callback when refresh is triggered
footer Widget false null Elements that will be displayed when pulling up
footerBuilder FooterBuilder false null Build pull-up loading elements. Will override [footer] configuration.
footerHeight double false 0.0 [footer] The height of the area
footerTrigger double false 0.0 The distance to trigger the pull-up loading should be greater than [headerHeight]
shouldLoad bool false true Whether the pull-up load should be triggered. In some scenarios, when the loading is completed, the pull-up loading element will need to be turned into a footer
onLoad VoidCallback false null Callback when loading is triggered
controller FRefreshController false null [Refresh] controller. See [Refresh Controller] for details

⌨️ FRefreshController

🔧 Param

Param Type Desc
refreshState RefreshState Get the pull-down refresh status. See [RefreshState] for details
loadState LoadState Get the pull-up loading status. See [LoadState] for details
position double Current scroll position
scrollMetrics ScrollMetrics Current scroll information. See [ScrollMetrics] for details.
backOriginOnLoadFinish bool When loading is completed, whether to return to the original position. This parameter is useful when the GridView only adds one element.

📡 Interface

  • void refresh({Duration duration = const Duration(milliseconds: 300)})

Actively trigger pull-down refresh.

[duration] The duration of the pull-down effect. Default 300ms

  • finishRefresh()

End pull-down refresh.

  • finishLoad()

End pull-up loading.

  • void setOnStateChangedCallback(OnStateChangedCallback callback)

Set up status listener. e.g .:

  if (state is RefreshState) {

  if (state is LoadState) {


  • void setOnScrollListener(OnScrollListener onScrollListener)

Set up scroll listener. Receive [ScrollMetrics].

  • void scrollTo(double position, {Duration duration = const Duration(milliseconds: 300)})

Scroll to the specified position.

  • void scrollBy(double offset, {Duration duration = const Duration(milliseconds: 300)})

Scroll the specified distance.

  • void jumpTo(double position)

Jump to the specified position.

🃏 RefreshState

Value Desc
PREPARING_REFRESH Reach [headerTrigger], ready to enter refresh state
FINISHING Refresh ending
IDLE Idle state

🃏 LoadState

Value Desc
PREPARING_LOAD Reach [footerTrigger], ready to enter the loading state
FINISHING Load ending
IDLE Idle state

📺 Demo

🔩 Refresh Example

Lazy Loading Flutter

This is our most common pull-down refresh example in daily development 🌰. Believe me, if you want to build such an effect, it will be very difficult!

But if you use FRefresh, the situation is completely different.

Next, we only need a few lines of code to complete the construction of this effect.

1. Create FRefreshController

/// Create a controller
FRefreshController controller = FRefreshController()

2. Create FRefresh


  /// Set up the controller
  controller: controller,

  /// create Header
  header: buildRefreshView(),

  /// Need to pass the size of the header area
  headerHeight: 75.0,

  /// Content area widget
  child: ListView.builder(
      physics: NeverScrollableScrollPhysics(),
      shrinkWrap: true,

  /// This function will be called back after entering Refreshing
  onRefresh: () {

     /// End refresh via controller

Done 🔨!

This is all you need to do to create a pull-down refresh.

FRefresh takes care of everything, developers only need to focus on the construction of the Header area and content area.

⚠️ Attention,To use ListView, GridView in FRefresh, you need to configure their physics: NeverScrollableScrollPhysics (), shrinkWrap: true, otherwise it will affect the scrolling and layout effects.

🔩 HeaderBuilder Demo

Lazy Loading Flutter

  controller: controller,

  /// Build the header area with headerBuilder
  headerBuilder: (setter, constraints) {
    return FSuper(

       /// Get the available space in the current header area
       width: constraints.maxWidth,
       height: constraints.maxHeight,
             /// Refresh the header area
  headerHeight: 100.0,

  /// Build content area
  child: GridView.builder(),

  /// This function will be called back after entering the refreshing state
  onRefresh: () {

    /// finish refresh

FRefresh provides a very flexible Header area construction method, which is to complete the construction through the HeaderBuilder function.

In the HeaderBuilder function, the developer can get the refresh function StateSetter for the partial refresh Header area and the real-time size of the Header area through the parameters.

This way, the Header area is given more open creativity.

🔭 Load Example

Corresponding to the pull-down refresh, the construction of the pull-up loading effect is also very simple.

1. Create FRefreshController

/// Create a controller
FRefreshController controller = FRefreshController()

2. Create FRefresh


  /// Setup the controller
  controller: controller,

  /// create Footer area
  footer: LinearProgressIndicator(),

  /// need to setup Footer area height
  footerHeight: 20.0,

  /// create content area
  child: builderContent(),

  /// This function will be called back after entering the Loading state
  onLoad: () {

    /// End loading state

Building pull-ups is equally simple enough. Developers only need to pay attention to the construction of Footer area and content area, and the state changes and visual effects control during the pull-up loading process can be safely handed over to FRefresh.

🔭 FooterBuilder Demo

Lazy Loading Flutter

  controller: controller,

  /// Build Footer Area Widget by FooterBuilder
  footerBuilder: (setter) {

    /// Get refresh status, partially update the content of Footer area
    controller.setOnStateChangedCallback((state) {
      setter(() {
    return buildFooter();
  footerHeight: 38.0,
  child: buildContent(),
  onLoad: () {

FRefresh also provides a builder function FooterBuilder for building the Footer area. Through this function, you can get the refresh function StateSetter which refreshes only the Footer area.

In this way, the developer can easily change the view of the footer area according to the status or some other conditions. Very intimate 🥰.

⚙️ FRefreshController

Lazy Loading Flutter

FRefresh provides developers with intimate controllers FRefreshController, which supports many convenient capabilities.

1. Add controller to FRefresh

/// Create Controller
FRefreshController controller = FRefreshController()

/// Configure controller for FRefresh
  controller: controller,

When the developer creates a controller and then sets it into a FRefresh, the controller can start to monitor the status of this FRefresh and control it.

2. Stop refreshing or loading

When the refresh state or loading state is triggered, data processing tasks such as network requests are usually performed. After these tasks are completed, we need to stop the refresh state or loading state. How to do it?

  • controller.finishRefresh() Can stop refreshing

  • controller.finishLoad() Can stop loading

3. State Change Listen

controller5.setOnStateChangedCallback((state) {
  /// Refresh status
  if (state is RefreshState) {
  /// Loading state
  if (state is LoadState) {

Through the above simple code, you can monitor the status change of FRefresh, whether it is pull-down refresh or pull-up loading.

4. Scroll Listen

controller.setOnScrollListener((metrics) {
  /// Get scroll information

FRefreshController It is really convenient to add sliding monitor. The parameters received is [ScrollMetrics],it can get very comprehensive information such as current scroll distance, maximum scroll distance, whether it exceeds the scroll range, etc..

5. Actively trigger refresh

Through FRefreshController, developers can also actively trigger a refresh, and can specify the length of time to slide to the refresh position.

controller.refresh(duration: Duration(milliseconds: 2000));

This feature is very useful in many scenarios.

6. Scroll control

FRefreshController provides a variety of intimate and delicate sliding controls for developers to choose.

/// Scroll to the specified position
controller.scrollTo(100.0, duration:Duration(milliseconds: 2000));

/// Scroll the specified distance
controller.scrollBy(20.0, duration:Duration(milliseconds: 800));

/// Jump to the specified position

This makes many beautiful interactions easier to build.

😃 How to use?

Add dependencies in the project pubspec.yaml file:

🌐 pub dependency

  frefresh: ^<version number>

⚠️ Attention,please go to [pub] ( to get the latest version number of FRefresh

🖥 Git dependency

      url: ''
      ref: '<Branch number or tag number>'

⚠️ Attention,please refer to [FRefresh] ( official project for branch number or tag.

💡 License

Copyright 2020-present Fliggy Android Team <>.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at following link.

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
See the License for the specific language governing permissions and
limitations under the License.

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How to run Demo project?

  1. clone project to local

  2. Enter the project example directory and run the following command

flutter create .
  1. Run the demo in example

Source Code

Please Visit Lazy Loading Flutter Source Code at GitHub