Scribble Text Input Client

Adds three methods, showToolbar, insertTextPlaceholder, and removeTextPlaceholder to the TextInputClient interface to allow the iOS 14 Scribble feature to insert and remove text placeholders and show the toolbar.

As of iOS 14, iPads support the Scribble feature when using the Apple Pencil. This feature allows users to use the pencil to interact with text fields to add, delete, select, and modify text.

In native text widgets, the text toolbar is shown when a user uses the pencil to select text on an iPad running iOS 14 or higher. To replicate this behavior, the platform sends a textInput channel message called TextInputClient.showToolbar. This notifies the Dart code that the toolbar should be shown.

When a user holds the pencil down, a visual gap in the text is shown to allow the user extra space to write. To replicate this behavior, the platform sends textInput channel messages called TextInputClient.insertTextPlaceholder and TextInputClient.removeTextPlaceholder. Multiline text inputs should have placeholders that provide vertical space, while single line inputs should provide horizontal space.

If you previously implemented TextEditingClient, you must override showToolbar, insertTextPlaceholder, and removeTextPlaceholder to either support these Scribble features or provide an empty implementation.

To migrate, implement showToolbar, insertTextPlaceholder, and removeTextPlaceholder.

Code before migration:

class MyCustomTextInputClient implements TextInputClient {
  ...
}

Code after migration:

class MyCustomTextInputClient implements TextInputClient {
  ...
  @override
  void showToolbar() {
    ...
  }
  
  @override
  void insertTextPlaceholder(Size size) {
    ...
  }
  
  @override
  void removeTextPlaceholder() {
    ...
  }
}

Landed in version: 2.9.0-1.0.pre
In stable release: 2.10

API documentation:

• TextInputClient

Relevant issues:

• Issue 61278

Relevant PRs:

• 24224: Support Scribble Handwriting (engine)
• 75472: Support Scribble Handwriting
• 97437: Re-land Support Scribble Handwriting

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