AppFlowy/frontend/app_flowy/packages/flowy_editor/documentation/customizing.md

# How to customizing ...

## Customizing a shortcut event
we will use a simple example to describe how to quickly extend shortcut event.

For example, typing `_xxx_` will be converted into _xxx_.

To start with, we build the simplest example, just a blank document.

```dart
@override
Widget build(BuildContext context) {
  return Scaffold(
    body: Container(
      alignment: Alignment.topCenter,
      child: FlowyEditor(
        editorState: EditorState.empty(),
        keyEventHandlers: const [],
      ),
    ),
  );
}
```

Nothing will happen after typing `_xxx_`.

![Before](./images/customizing_a_shortcut_event_before.gif)

Next, we will create a function to handler underscore input.

```dart
import 'package:flowy_editor/flowy_editor.dart';
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';

FlowyKeyEventHandler underscoreToItalicHandler = (editorState, event) {
  // Since we only need to handler the input of `underscore`.
  // All inputs except `underscore` will be ignored directly.
  if (event.logicalKey != LogicalKeyboardKey.underscore) {
    return KeyEventResult.ignored;
  }
};
```

Then, we need to determine if the currently selected node is `TextNode` and is a single-select case, because for the multi-select case, underscore input should be considered as replacement.

```dart
// ...
FlowyKeyEventHandler underscoreToItalicHandler = (editorState, event) {
  // ...
  
  // Obtaining the selection and selected nodes of the current document through `selectionService`.
  // And determine whether it is a single selection and whether the selected node is a text node.
  final selectionService = editorState.service.selectionService;
  final selection = selectionService.currentSelection.value;
  final textNodes = selectionService.currentSelectedNodes.whereType<TextNode>();
  if (selection == null || !selection.isSingle || textNodes.length != 1) {
    return KeyEventResult.ignored;
  }
```

Now, we start working on underscore logic by looking for the position of the previous underscore and returning if not found. If found, the text wrapped in the two underscores will be converted info italic.

```dart
// ...
FlowyKeyEventHandler underscoreToItalicHandler = (editorState, event) {
  // ...

  final textNode = textNodes.first;
  final text = textNode.toRawString();
  // Determine if `underscore` already exists in the text node
  final previousUnderscore = text.indexOf('_');
  if (previousUnderscore == -1) {
    return KeyEventResult.ignored;
  }

  // Delete the previous `underscore`,
  // update the style of the text surrounded by two underscores to `italic`,
  // and update the cursor position.
  TransactionBuilder(editorState)
    ..deleteText(textNode, previousUnderscore, 1)
    ..formatText(
      textNode,
      previousUnderscore,
      selection.end.offset - previousUnderscore - 1,
      {'italic': true},
    )
    ..afterSelection = Selection.collapsed(
      Position(path: textNode.path, offset: selection.end.offset - 1),
    )
    ..commit();

  return KeyEventResult.handled;
};
```

So far, the 'underscore handler' function has completed and only needs to be injected info AppFlowyEditor.

```dart
@override
Widget build(BuildContext context) {
  return Scaffold(
    body: Container(
      alignment: Alignment.topCenter,
      child: FlowyEditor(
        editorState: EditorState.empty(),
        keyEventHandlers: [
            underscoreToItalicHandler,
        ],
      ),
    ),
  );
}
```

![After](./images/customizing_a_shortcut_event_after.gif)

[Complete code example]()

## Customizing a component
we will use a simple example to describe how to quickly extend custom component.

For example, we want to render an image from network.

To start with, we build the simplest example, just a blank document.

```dart
@override
Widget build(BuildContext context) {
  return Scaffold(
    body: Container(
      alignment: Alignment.topCenter,
      child: FlowyEditor(
        editorState: EditorState.empty(),
        keyEventHandlers: const [],
      ),
    ),
  );
}
```

Next, we choose a unique string for the type of the custom node and use `network_image` in this case. And we add `network_image_src` to the `attributes` to describe the link of the image.

> For the definition of the [Node](), please refer to this [link]().

```JSON
{
  "type": "network_image",
  "attributes": {
    "network_image_src": "https://docs.flutter.dev/assets/images/dash/dash-fainting.gif"
  }
}
```

Then, we create a class that inherits [NodeWidgetBuilder](). As shown in the autoprompt, we need to implement two functions, one that returns a widget and the other that verifies the correctness of the [Node]().


```dart
import 'package:flowy_editor/flowy_editor.dart';
import 'package:flutter/material.dart';

class NetworkImageNodeWidgetBuilder extends NodeWidgetBuilder {
  @override
  Widget build(NodeWidgetContext<Node> context) {
    throw UnimplementedError();
  }

  @override
  NodeValidator<Node> get nodeValidator => throw UnimplementedError();
}
```

Now, let's implement a simple image widget based on `Image`.

**It is important to note that the `State` of the returned `Widget` must be with [Selectable]().**

> For the definition of the [Selectable](), please refer to this [link]().

```dart
class _NetworkImageNodeWidget extends StatefulWidget {
  const _NetworkImageNodeWidget({
    Key? key,
    required this.node,
  }) : super(key: key);

  final Node node;

  @override
  State<_NetworkImageNodeWidget> createState() =>
      __NetworkImageNodeWidgetState();
}

class __NetworkImageNodeWidgetState extends State<_NetworkImageNodeWidget>
    with Selectable {
  RenderBox get _renderBox => context.findRenderObject() as RenderBox;

  @override
  Widget build(BuildContext context) {
    return Image.network(
      widget.node.attributes['network_image_src'],
      height: 200,
      loadingBuilder: (context, child, loadingProgress) =>
          loadingProgress == null ? child : const CircularProgressIndicator(),
    );
  }

  @override
  Position start() => Position(path: widget.node.path, offset: 0);

  @override
  Position end() => Position(path: widget.node.path, offset: 1);

  @override
  Position getPositionInOffset(Offset start) => end();

  @override
  List<Rect> getRectsInSelection(Selection selection) =>
      [Offset.zero & _renderBox.size];

  @override
  Selection getSelectionInRange(Offset start, Offset end) => Selection.single(
        path: widget.node.path,
        startOffset: 0,
        endOffset: 1,
      );

  @override
  Offset localToGlobal(Offset offset) => _renderBox.localToGlobal(offset);
}
```

Finally, we return `_NetworkImageNodeWidget` in the `build` function of `NetworkImageNodeWidgetBuilder` and register `NetworkImageNodeWidgetBuilder` into `AppFlowyEditor`.

```dart
class NetworkImageNodeWidgetBuilder extends NodeWidgetBuilder {
  @override
  Widget build(NodeWidgetContext<Node> context) {
    return _NetworkImageNodeWidget(
      key: context.node.key,
      node: context.node,
    );
  }

  @override
  NodeValidator<Node> get nodeValidator => (node) {
        return node.type == 'network_image' &&
            node.attributes['network_image_src'] is String;
      };
}
```

```dart
final editorState = EditorState(
  document: StateTree.empty()
    ..insert(
      [0],
      [
        TextNode.empty(),
        Node.fromJson({
          'type': 'network_image',
          'attributes': {
            'network_image_src':
                'https://docs.flutter.dev/assets/images/dash/dash-fainting.gif'
          }
        })
      ],
    ),
);
return FlowyEditor(
  editorState: editorState,
  customBuilders: {
    'network_image': NetworkImageNodeWidgetBuilder(),
  },
);
```

![](./images/customizing_a_component.gif)

[Complete code example]()