BranchLine class abstract

Abstract base class for defining tree branch line styles.

BranchLine defines how visual connections are drawn between parent and child nodes in tree views. Different implementations provide various visual styles from no lines to complex path-based connections.

The class provides static instances for common branch line styles:

• BranchLine.none - No visual connections
• BranchLine.line - Simple vertical lines
• BranchLine.path - Connected path lines showing hierarchy

Custom implementations can be created by extending this class and implementing the build method to return appropriate connection widgets.

Example:

// Using built-in styles
TreeView(
  branchLine: BranchLine.path, // Connected paths
  // ... other properties
);

// Custom branch line implementation
class CustomBranchLine extends BranchLine {
  @override
  Widget build(BuildContext context, List<TreeNodeDepth> depth, int index) {
    return CustomPaint(painter: MyCustomLinePainter());
  }
}