ViewHolder

The ViewHolder pattern is a design pattern used in Android development, primarily within RecyclerView, to improve the performance of scrolling lists. Its main purpose is to reduce the number of times findViewById is called, which is an expensive operation.

In a typical ListView or older RecyclerView implementations, as items scrolled on and off the screen, their views would be inflated and findViewById would be called repeatedly to find child views within each list item's layout. This led to significant performance degradation, especially with large datasets.

The ViewHolder pattern addresses this by introducing a holder object that stores references to the views within a list item. When a new item view is created, a ViewHolder is also created and its child views are found using findViewById only once. The ViewHolder then holds these references. As the list scrolls and views are recycled, instead of calling findViewById again, the ViewHolder's cached references are used to update the recycled view's content. This significantly speeds up the process of updating list items.

Implementing the ViewHolder pattern involves creating a custom class that extends RecyclerView.ViewHolder and holds references to the views that need to be updated. This pattern is fundamental to efficient list rendering in modern Android applications.