build method

  1. @override
Widget build(
  1. BuildContext context
)
override

Describes the part of the user interface represented by this widget.

The framework calls this method when this widget is inserted into the tree in a given BuildContext and when the dependencies of this widget change (e.g., an InheritedWidget referenced by this widget changes). This method can potentially be called in every frame and should not have any side effects beyond building a widget.

The framework replaces the subtree below this widget with the widget returned by this method, either by updating the existing subtree or by removing the subtree and inflating a new subtree, depending on whether the widget returned by this method can update the root of the existing subtree, as determined by calling Widget.canUpdate.

Typically implementations return a newly created constellation of widgets that are configured with information from this widget's constructor and from the given BuildContext.

The given BuildContext contains information about the location in the tree at which this widget is being built. For example, the context provides the set of inherited widgets for this location in the tree. A given widget might be built with multiple different BuildContext arguments over time if the widget is moved around the tree or if the widget is inserted into the tree in multiple places at once.

The implementation of this method must only depend on:

If a widget's build method is to depend on anything else, use a StatefulWidget instead.

See also:

  • StatelessWidget, which contains the discussion on performance considerations.

Implementation

@override
Widget build(BuildContext context) {
  return GestureDetector(
    // Detect horizontal dragging to change the progress value
    onHorizontalDragUpdate: (details) {
      // Calculate the new progress by adding the change in horizontal drag
      double newProgress =
          (progress + details.primaryDelta! / context.size!.width).clamp(0.0,
              1.0); // Ensure the progress stays within the range [0.0, 1.0]

      // Invoke the seekTo callback to update the progress
      seekTo(newProgress);
    },
    onHorizontalDragEnd: (details) {
      // When the drag ends, seek to the current progress (this may be redundant but ensures the final position is set)
      seekTo(progress);
    },
    child: AnimatedContainer(
      // Container that animates changes to its height and color
      duration: const Duration(
          milliseconds: 200), // Duration for the smooth animation
      height: progressBarHeight, // Set the height of the progress bar
      color:
          progressBarBackgroundColor, // Set the background color of the progress bar
      child: LinearProgressIndicator(
        // Linear progress indicator to visually show progress
        value: progress, // Bind the current progress value
        backgroundColor: Colors
            .transparent, // Make the background transparent to show the progress bar properly
        valueColor: AlwaysStoppedAnimation<Color>(
            progressBarColor), // Set the color of the progress indicator
      ),
    ),
  );
}