### Basic ListView Setup

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/2、Scrolling-to-the-specified-index-location

Demonstrates the basic setup for a ListView with ScrollController and ListObserverController.

```dart
ScrollController scrollController = ScrollController();

ListView _buildListView() {
  return ListView.separated(
    controller: scrollController,
    ...
  );
}
```

```dart
ListObserverController observerController = ListObserverController(controller: scrollController);

ListViewObserver(
  controller: observerController,
  child: _buildListView(),
  ...
)
```

--------------------------------

### SliverAppBar Configuration

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/2、Scrolling-to-the-specified-index-location

Example configuration for a SliverAppBar, which is often used in scenarios requiring dynamic scroll offsets.

```dart
SliverAppBar(
  key: appBarKey,
  pinned: true,
  expandedHeight: 200,
  flexibleSpace: FlexibleSpaceBar(
    title: const Text('AppBar'),
    background: Container(color: Colors.orange),
  ),
);
```

--------------------------------

### CustomScrollView Setup with SliverViewObserver

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/2、Scrolling-to-the-specified-index-location

Shows how to integrate SliverViewObserver with CustomScrollView for observing slivers like SliverList and SliverGrid.

```dart
SliverViewObserver(
  controller: observerController,
  child: CustomScrollView(
    controller: scrollController,
    slivers: [
      _buildSliverListView1(),
      _buildSliverListView2(),
    ],
  ),
  sliverListContexts: () {
    return [
      if (_sliverViewCtx1 != null) _sliverViewCtx1!,
      if (_sliverViewCtx2 != null) _sliverViewCtx2!,
    ];
  },
  ...
)
```

--------------------------------

### Set Initial Index (Simple)

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/2、滚动到指定下标位置

Sets the initial scroll index using the `initialIndex` property for a ListObserverController. This is the simplest way to specify the starting position.

```dart
observerController = ListObserverController(controller: scrollController)
  ..initialIndex = 10;
```

--------------------------------

### Listening to Scroll State Notifications in Flutter

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/2、Scrolling-to-the-specified-index-location

Use NotificationListener with ObserverScrollNotification to detect different scrolling states like start, interruption, decision, and end. This is useful for managing UI updates or performing actions based on scroll events.

```dart
NotificationListener<ObserverScrollNotification>(
  child: widget,
  onNotification: (notification) {
    if (notification is ObserverScrollStartNotification) {
      
    } else if (notification is ObserverScrollInterruptionNotification) {
      
    } else if (notification is ObserverScrollDecisionNotification) {
      
    } else if (notification is ObserverScrollEndNotification) {
      
    }
    return true;
  },
);
```

--------------------------------

### Initialize ListObserverController and ChatScrollObserver

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/3、Chat-Observer

Initialize ListObserverController and ChatScrollObserver for chat list observation. Configure the fixed position offset and a callback for rebuilding the scroll view.

```dart
/// Initialize ListObserverController
observerController = ListObserverController(controller: scrollController)
  ..cacheJumpIndexOffset = false;

/// Initialize ChatScrollObserver
chatObserver = ChatScrollObserver(observerController)
  // Greater than this offset will be fixed to the current chat position.
  ..fixedPositionOffset = 5
  ..toRebuildScrollViewCallback = () {
    // Here you can use other way to rebuild the specified listView instead of [setState]
    setState(() {});
  };
```

--------------------------------

### Configure ListView with ListViewObserver

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/3、Chat-Observer

Configure the ListView with ChatObserverClampingScrollPhysics and wrap it with ListViewObserver. Ensure shrinkWrap is set according to the observer's state.

```dart
Widget _buildListView() {
  Widget resultWidget = ListView.builder(
    physics: ChatObserverClampingScrollPhysics(observer: chatObserver),
    shrinkWrap: chatObserver.isShrinkWrap,
    reverse: true,
    controller: scrollController,
    ...
  );

  resultWidget = ListViewObserver(
    controller: observerController,
    child: resultWidget,
  );
  return resultWidget;
}
```

--------------------------------

### 手动触发 ListView 观察

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/1、监听滚动视图中正在显示的子部件

当需要手动触发一次 ListView 的观察时，可以使用 ListViewOnceObserveNotification 并将其 dispatch 到目标 BuildContext。

```dart
ListViewOnceObserveNotification().dispatch(_sliverListViewContext);
```

--------------------------------

### 使用 ListObserverController 手动触发观察

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/1、监听滚动视图中正在显示的子部件

通过创建 ListObserverController 实例并将其传递给 ListViewObserver 的 controller 参数，可以手动调用 dispatchOnceObserve 方法来触发一次观察。这在需要主动获取滚动状态时非常有用。

```dart
// 创建 `ListObserverController` 实例
ListObserverController controller = ListObserverController();
...

// 传递给 `ListViewObserver` 的 `controller` 参数
ListViewObserver(
  ...
  controller: controller,
  ...
)
...

// 手动触发一次观察
controller.dispatchOnceObserve();
```

--------------------------------

### Define Executable and Link Libraries

Source: https://github.com/fluttercandies/flutter_scrollview_observer/blob/main/example/windows/runner/CMakeLists.txt

Configures the main executable for the Windows runner, specifying source files, applying standard settings, defining preprocessor macros, linking necessary libraries, and setting include directories. It also adds a dependency on the flutter_assemble target.

```cmake
cmake_minimum_required(VERSION 3.14)
project(runner LANGUAGES CXX)

add_executable(${BINARY_NAME} WIN32
  "flutter_window.cpp"
  "main.cpp"
  "utils.cpp"
  "win32_window.cpp"
  "${FLUTTER_MANAGED_DIR}/generated_plugin_registrant.cc"
  "Runner.rc"
  "runner.exe.manifest"
)
apply_standard_settings(${BINARY_NAME})
target_compile_definitions(${BINARY_NAME} PRIVATE "NOMINMAX")
target_link_libraries(${BINARY_NAME} PRIVATE flutter flutter_wrapper_app)
target_include_directories(${BINARY_NAME} PRIVATE "${CMAKE_SOURCE_DIR}")
add_dependencies(${BINARY_NAME} flutter_assemble)
```

--------------------------------

### 使用 ListViewObserver 监听 Sliver

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/1、监听滚动视图中正在显示的子部件

通过 ListViewObserver 包装 ListView，并提供 sliverListContexts 回调来指定要观察的 Sliver 的 BuildContext。onObserveAll 回调用于处理观察结果。

```dart
ListViewObserver(
  child: _buildListView(),
  sliverListContexts: () {
    return [if (_sliverListViewContext != null) _sliverListViewContext!];
  },
  onObserveAll: (resultMap) {
    final model = resultMap[_sliverListViewContext];
    if (model == null) return;

    // 打印当前正在显示的第一个子部件
    print('firstChild.index -- ${model.firstChild?.index}');

    // 打印当前正在显示的所有子部件下标
    print('displaying -- ${model.displayingChildIndexList}');
  },
)
```

--------------------------------

### 常规方式使用 ListViewObserver

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/1、监听滚动视图中正在显示的子部件

将 ListViewObserver 作为父组件包裹 ListView，并通过 onObserve 回调获取滚动视图中第一个 Sliver 的观察结果。默认在 ListView 滚动时触发。

```dart
ListViewObserver(
  child: _buildListView(),
  onObserve: (resultModel) {
    print('firstChild.index -- ${resultModel.firstChild?.index}');
    print('displaying -- ${resultModel.displayingChildIndexList}');
  },
)
```

--------------------------------

### ListObserverController.dispatchOnceObserve 方法定义

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/1、监听滚动视图中正在显示的子部件

该方法用于手动触发一次观察，并可以返回观察结果。支持通过 sliverContext 指定观察的滚动视图上下文，isForce 参数用于强制触发，isDependObserveCallback 参数控制是否依赖于 onObserve 回调的实现。

```dart
Future<ListViewOnceObserveNotificationResult> dispatchOnceObserve({
  BuildContext? sliverContext,
  bool isForce = false,
  bool isDependObserveCallback = true,
})
```

--------------------------------

### 记录 ListView 的 BuildContext

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/1、监听滚动视图中正在显示的子部件

在 ListView 的 itemBuilder 回调中记录当前 BuildContext。当存在多个 Sliver 时，此方法可能需要使用。

```dart
BuildContext? _sliverListViewContext;

ListView _buildListView() {
  return ListView.separated(
    itemBuilder: (ctx, index) {
      if (_sliverListViewContext != ctx) {
        _sliverListViewContext = ctx;
      }
      ...
    },
    ...
  );
}
```

--------------------------------

### Scrolling with Dynamic Offset Calculation

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/2、Scrolling-to-the-specified-index-location

Demonstrates how to use the `animateTo` method with a custom `offset` callback to handle dynamic scroll view heights, such as those with a SliverAppBar.

```dart
observerController.animateTo(
  ...
  offset: (offset) {
    // The height of the SliverAppBar is calculated base on target offset and is returned in the current callback.
    // The observerController internally adjusts the appropriate offset based on the return value.
    return ObserverUtils.calcPersistentHeaderExtent(
      key: appBarKey,
      offset: offset,
    );
  },
);
```

--------------------------------

### Import scrollview_observer Package

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/Home

Import the necessary package in your Dart files where you intend to use the ScrollView observer functionality.

```dart
import 'package:scrollview_observer/scrollview_observer.dart';
```

--------------------------------

### 使用 SliverViewObserver 观察 CustomScrollView 的 Viewport

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/1、监听滚动视图中正在显示的子部件

SliverViewObserver 用于观察 CustomScrollView 的 Viewport 中哪些指定的 Sliver 正在展示。sliverContexts 参数传入的是外层 Sliver 的 BuildContext。

```dart
SliverViewObserver(
  child: _buildScrollView(),
  sliverContexts: () {
    return [
      if (grid1Context != null) grid1Context!,
      if (swipeContext != null) swipeContext!,
      if (grid2Context != null) grid2Context!,
    ];
  },
  onObserveViewport: (result) {
    firstChildCtxInViewport = result.firstChild.sliverContext;
    if (firstChildCtxInViewport == grid1Context) {
      debugPrint('current first sliver in viewport - gridView1');
    } else if (firstChildCtxInViewport == swipeContext) {
      debugPrint('current first sliver in viewport - swipeView');
    } else if (firstChildCtxInViewport == grid2Context) {
      debugPrint('current first sliver in viewport - gridView2');
    }
  },
)
```

--------------------------------

### Configure Chat Observer for Specified Item Mode

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/3、Chat-Observer

Use this configuration when dealing with discontinuous generative messages or simultaneous add/delete operations. Set `mode` to `.specified` and provide relevant `refItemIndex` values.

```dart
chatObserver.standby(
  mode: ChatScrollObserverHandleMode.specified,
  refIndexType: ChatScrollObserverRefIndexType.relativeIndexStartFromCacheExtent,
  refItemIndex: 2,
  refItemIndexAfterUpdate: 2,
);
```

--------------------------------

### Add scrollview_observer to pubspec.yaml

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/Home

To use the scrollview_observer package, add it as a dependency in your pubspec.yaml file. Replace 'latest_version' with the actual latest version number.

```yaml
dependencies:
  scrollview_observer: latest_version
```

--------------------------------

### Set Initial Index with Model

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/2、滚动到指定下标位置

Configures the initial scroll index using `initialIndexModel` with an ObserverIndexPositionModel. This allows for more detailed control over the initial position, including alignment and fixed height.

```dart
observerController = ListObserverController(controller: scrollController)
  ..initialIndexModel = ObserverIndexPositionModel(
    index: 10,
    isFixedHeight: true,
    alignment: 0.5,
  );
```

--------------------------------

### 自定义观察逻辑

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/1、监听滚动视图中正在显示的子部件

使用 customHandleObserve 回调来自定义观察逻辑，当库自带的处理逻辑不满足需求时使用。

```dart
customHandleObserve: (context) {
  // 完全自定义你的观察逻辑
  final _obj = ObserverUtils.findRenderObject(context);
  if (_obj is RenderSliverList) {
    ObserverCore.handleListObserve(context: context);
  }
  if (_obj is RenderSliverGrid || _obj is RenderSliverWaterfallFlow) {
    return ObserverCore.handleGridObserve(context: context);
  }
  return null;
},
```

--------------------------------

### Observe Sliver Children with ListViewObserver and sliverListContexts

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/1、Observing-child-widgets-those-are-being-displayed-in-the-ScrollView

Observe child widgets within specific Slivers using ListViewObserver by providing a function that returns a list of sliverContexts. The onObserveAll callback receives a map of results keyed by BuildContext.

```dart
ListViewObserver(
  child: _buildListView(),
  sliverListContexts: () {
    return [if (_sliverListViewContext != null) _sliverListViewContext!];
  },
  onObserveAll: (resultMap) {
    final model = resultMap[_sliverListViewContext];
    if (model == null) return;

    // Prints the first child widget index that is currently being displayed
    print('firstChild.index -- ${model.firstChild?.index}');

    // Prints the index of all child widgets those are currently being displayed
    print('displaying -- ${model.displayingChildIndexList}');
  },
)
```

--------------------------------

### Handling Dynamic Headers with Offset Parameter

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/2、滚动到指定下标位置

Use the offset parameter to manage scroll offsets when dealing with dynamic headers like SliverAppBar, ensuring correct positioning as the header's height changes.

```dart
SliverAppBar(
  key: appBarKey,
  pinned: true,
  expandedHeight: 200,
  flexibleSpace: FlexibleSpaceBar(
    title: const Text('AppBar'),
    background: Container(color: Colors.orange),
  ),
);
```

```dart
observerController.animateTo(
  ...
  offset: (offset) {
    // 根据目标偏移量 offset，计算出 SliverAppBar 的高度并返回
    // observerController 内部会根据该返回值做适当的偏移调整
    return ObserverUtils.calcPersistentHeaderExtent(
      key: appBarKey,
      offset: offset,
    );
  },
);
```

--------------------------------

### Record BuildContext for Sliver ListView

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/1、Observing-child-widgets-those-are-being-displayed-in-the-ScrollView

Record the BuildContext of a ListView within its itemBuilder callback. This is necessary when using the specific Sliver observation method to identify the ListView.

```dart
ListView _buildListView() {
  return ListView.separated(
    itemBuilder: (ctx, index) {
      if (_sliverListViewContext != ctx) {
        _sliverListViewContext = ctx;
      }
      ...
    },
    ...
  );
}
```

--------------------------------

### ObserverIndexPositionModel Definition

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/2、滚动到指定下标位置

Defines the parameters for configuring an initial scroll position, including index, context, height, alignment, offset, and padding.

```dart
ObserverIndexPositionModel({
  required this.index,
  this.sliverContext,
  this.isFixedHeight = false,
  this.alignment = 0,
  this.offset,
  this.padding = EdgeInsets.zero,
});
```

--------------------------------

### Setting Padding for ScrollViewObserver

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/2、滚动到指定下标位置

When using padding with ListView or GridView, ensure the same padding value is provided to the observerController for accurate scrolling.

```dart
ListView.separated(padding: _padding, ...);
GridView.builder(padding: _padding, ...);
```

```dart
observerController.jumpTo(index: 1, padding: _padding);
```

--------------------------------

### Jump to Index (No Animation)

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/2、Scrolling-to-the-specified-index-location

Scrolls the ListView to the specified index without any animation.

```dart
// Jump to the specified index position without animation.
observerController.jumpTo(index: 1)
```

--------------------------------

### Cache Extent Calculation Formula

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/3、Chat-Observer

Formula for calculating cacheExtent to avoid issues when inserting many messages at once. Ensure the reference message view can be rendered.

```plaintext
cacheExtent = [maximum height of a message] * [number of messages inserted at one time] + 200
```

--------------------------------

### Custom Observation Logic

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/1、Observing-child-widgets-those-are-being-displayed-in-the-ScrollView

Implement customHandleObserve to define your own observation logic when the built-in methods are insufficient. It allows for custom handling of different RenderSliver types.

```dart
customHandleObserve: (context) {
  // Here you can customize the observation logic.
  final _obj = ObserverUtils.findRenderObject(context);
  if (_obj is RenderSliverList) {
    ObserverCore.handleListObserve(context: context);
  }
  if (_obj is RenderSliverGrid || _obj is RenderSliverWaterfallFlow) {
    return ObserverCore.handleGridObserve(context: context);
  }
  return null;
},
```

--------------------------------

### Manually Trigger ScrollView Observation with ListObserverController

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/1、Observing-child-widgets-those-are-being-displayed-in-the-ScrollView

Manually trigger observations for a ScrollView using ListObserverController. Instantiate the controller, pass it to ListViewObserver, and then call dispatchOnceObserve() to force an observation.

```dart
// Create an instance of [ListObserverController]
ListObserverController controller = ListObserverController();
...

// Pass the controller instance to the 'controller' parameter of 'ListViewObserver'
ListViewObserver(
  ...
  controller: controller,
  ...
)
...

// Trigger an observation manually.
controller.dispatchOnceObserve();
```

--------------------------------

### Animate to Index

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/2、Scrolling-to-the-specified-index-location

Scrolls the ListView to the specified index with a smooth animation.

```dart
// Jump to the specified index position with animation.
observerController.animateTo(
  index: 1,
  duration: const Duration(milliseconds: 250),
  curve: Curves.ease,
);
```

--------------------------------

### ObserverTriggerOnObserveType 枚举

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/1、监听滚动视图中正在显示的子部件

配置触发 onObserve 和 onObserveAll 回调的前提条件，可以是直接返回数据或在显示项变化时返回。

```dart
enum ObserverTriggerOnObserveType {
  directly,
  displayingItemsChange,
}
```

--------------------------------

### Set Initial Index with Model Block

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/2、滚动到指定下标位置

Uses `initialIndexModelBlock` to dynamically provide an ObserverIndexPositionModel. This is useful when parameters like sliverContext are not available at initialization.

```dart
observerController = SliverObserverController(controller: scrollController)
  ..initialIndexModelBlock = () {
    return ObserverIndexPositionModel(
      index: 6,
      sliverContext: _sliverListCtx,
      offset: calcPersistentHeaderExtent,
    );
  };
```

--------------------------------

### 自定义目标 RenderSliver 类型

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/1、监听滚动视图中正在显示的子部件

通过 customTargetRenderSliverType 回调，可以指定库需要处理的 RenderSliver 类型，以支持第三方库构建的列表。

```dart
customTargetRenderSliverType: (renderObj) {
  // 告诉该库它需要观察什么类型的RenderObject
  return renderObj is ExtendedRenderSliverList;
},
```

--------------------------------

### Handle Multiple Message Insertions

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/3、Chat-Observer

Insert multiple messages at once by passing the changeCount parameter to the standby method. This helps in managing the scroll position for bulk updates.

```dart
_addMessage(int count) {
  chatObserver.standby(changeCount: count);
  setState(() {
    needIncrementUnreadMsgCount = true;
    for (var i = 0; i < count; i++) {
      chatModels.insert(0, ChatDataHelper.createChatModel());
    }
  });
}
```

--------------------------------

### Extended Observation Logic

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/1、Observing-child-widgets-those-are-being-displayed-in-the-ScrollView

Use extendedHandleObserve to supplement the original observation logic, particularly for types like RenderSliverWaterfallFlow. Only supported by SliverViewObserver.

```dart
extendedHandleObserve: (context) {
  // An extension of the original observation logic.
  final _obj = ObserverUtils.findRenderObject(context);
  if (_obj is RenderSliverWaterfallFlow) {
    return ObserverCore.handleGridObserve(context: context);
  }
  return null;
},
```

--------------------------------

### ObserverAutoTriggerObserveType 枚举

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/1、监听滚动视图中正在显示的子部件

定义了自动触发观察的时机，包括滚动开始、滚动更新和滚动结束。

```dart
enum ObserverAutoTriggerObserveType {
  scrollStart,
  scrollUpdate,
  scrollEnd,
}
```

--------------------------------

### Extend ScrollView Observation Logic

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/1、监听滚动视图中正在显示的子部件

Use `extendedHandleObserve` to supplement the default observation logic for specific RenderObjects like `RenderSliverWaterfallFlow`.

```dart
extendedHandleObserve: (context) {
  // 在对原来的观察逻辑进行拓展
  final _obj = ObserverUtils.findRenderObject(context);
  if (_obj is RenderSliverWaterfallFlow) {
    return ObserverCore.handleGridObserve(context: context);
  }
  return null;
},
```

--------------------------------

### Chat Position Result Callback

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/3、Chat-Observer

Callback for processing chat position results after handling scroll events. Used to display unread message bubbles.

```dart
chatObserver = ChatScrollObserver(observerController)
  ..onHandlePositionResultCallback = (result) {
    switch (result.type) {
      case ChatScrollObserverHandlePositionType.keepPosition:
        // Keep the current chat position.
        // updateUnreadMsgCount(changeCount: result.changeCount);
        break;
      case ChatScrollObserverHandlePositionType.none:
        // Do nothing about the chat position.
        // updateUnreadMsgCount(isReset: true);
        break;
    }
  };
```

--------------------------------

### Set Minimum Observe Interval During Scrolling

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/1、监听滚动视图中正在显示的子部件

Configure `observeIntervalForScrolling` to set the minimum time between scroll observations, reducing observation frequency and improving performance. The default is `Duration.zero`.

```dart
final Duration observeIntervalForScrolling;

observerController.observeIntervalForScrolling = Duration(milliseconds: 500);
```

--------------------------------

### ChatScrollObserverRefIndexType Enum Definition

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/3、Chat-Observer

Defines different strategies for referencing items within the scroll view, crucial for accurate observer behavior during updates. Understand how `relativeIndexStartFromCacheExtent` and `relativeIndexStartFromDisplaying` calculate indices.

```dart
enum ChatScrollObserverRefIndexType {
  ///     relativeIndex        trailing
  ///
  ///           6         |     item16    | cacheExtent
  ///   ----------------- ----------------- 
  ///           5         |     item15    | 
  ///           4         |     item14    | 
  ///           3         |     item13    | displaying
  ///           2         |     item12    | 
  ///           1         |     item11    | 
  ///   ----------------- ----------------- 
  ///           0         |     item10    | cacheExtent <---- start
  ///
  ///                          leading
  relativeIndexStartFromCacheExtent,

  ///     relativeIndex        trailing
  ///
  ///           5         |     item16    | cacheExtent
  ///   ----------------- ----------------- 
  ///           4         |     item15    | 
  ///           3         |     item14    | 
  ///           2         |     item13    | displaying
  ///           1         |     item12    | 
  ///           0         |     item11    |             <---- start
  ///   ----------------- ----------------- 
  ///          -1         |     item10    | cacheExtent
  ///
  ///                          leading
  relativeIndexStartFromDisplaying,

  /// Directly specify the index of item.
  itemIndex,
}
```

--------------------------------

### Standby for Inserting or Removing Chat Data

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/3、Chat-Observer

Call the standby method of ChatScrollObserver before inserting or removing chat data. Use isRemove flag for removal operations.

```dart
onPressed: () {
  chatObserver.standby();
  setState(() {
    chatModels.insert(0, ChatDataHelper.createChatModel());
  });
},
...
onRemove: () {
  chatObserver.standby(isRemove: true);
  setState(() {
    chatModels.removeAt(index);
  });
},
```

--------------------------------

### Generative Message Position Keeping

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/3、Chat-Observer

Adjust the processing mode in the standby method to 'generative' for keeping message position with generative messages like ChatGPT. This mode requires continuous generative messages.

```dart
chatObserver.standby(
  mode: ChatScrollObserverHandleMode.generative,
  // changeCount: 1,
);
```

--------------------------------

### Animate to Index in Sliver

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/2、Scrolling-to-the-specified-index-location

Scrolls to a specific index within a particular sliver in a CustomScrollView.

```dart
observerController.animateTo(
  sliverContext: _sliverViewCtx2, // _sliverViewCtx1
  index: 10,
  duration: const Duration(milliseconds: 300),
  curve: Curves.easeInOut,
);
```

--------------------------------

### Optimizing Scroll Performance with isFixedHeight

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/2、滚动到指定下标位置

Use the isFixedHeight parameter when child widgets have a fixed height to improve performance. This feature supports various ScrollView types since version 1.17.0.

```dart
// 无动画滚动至下标位置
observerController.jumpTo(index: 150, isFixedHeight: true)
```

```dart
// 动画滚动至下标位置
observerController.animateTo(
  index: 150, 
  isFixedHeight: true,
  duration: const Duration(milliseconds: 250),
  curve: Curves.ease,
);
```

--------------------------------

### Reattach ScrollView Observer

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/1、监听滚动视图中正在显示的子部件

Call `reattach()` on the `observerController` when a scroll view is laid out conditionally after initialization, to ensure the observer can acquire its `BuildContext`.

```dart
observerController.reattach();
```

--------------------------------

### Specifying Render Sliver Type for Third-Party ScrollViews

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/2、滚动到指定下标位置

For third-party ScrollViews, use the renderSliverType parameter to specify the rendering type (list or grid) if it's not a standard SliverList or SliverGrid.

```dart
enum ObserverRenderSliverType {
  list,
  grid,
}
```

```dart
observerController.jumpTo(
  index: 13,
  isFixedHeight: true,
  renderSliverType: ObserverRenderSliverType.grid,
);
```

--------------------------------

### Clear Index Offset Cache Method

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/2、滚动到指定下标位置

Clears the offset cache used for jumping to a specified index. The sliverContext parameter is only needed when managing the ScrollView's BuildContext manually.

```dart
/// Clear the offset cache that jumping to a specified index location.
clearIndexOffsetCache(BuildContext? sliverContext) {
  ...
```

--------------------------------

### ObserverTriggerOnObserveType Enum

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/1、Observing-child-widgets-those-are-being-displayed-in-the-ScrollView

Defines when the onObserve callbacks are triggered. Defaults to displayingItemsChange.

```dart
final ObserverTriggerOnObserveType triggerOnObserveType;

enum ObserverTriggerOnObserveType {
  directly,
  displayingItemsChange,
}
```

--------------------------------

### Custom Target Render Sliver Type

Source: https://github.com/fluttercandies/flutter_scrollview_observer/wiki/1、Observing-child-widgets-those-are-being-displayed-in-the-ScrollView

Use customTargetRenderSliverType to specify the RenderSliver type for observation, useful for third-party packages. Only supported by ListViewObserver and GridViewObserver.

```dart
customTargetRenderSliverType: (renderObj) {
  // Here you tell the package what type of RenderObject it needs to observe.
  return renderObj is ExtendedRenderSliverList;
},
```

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