The Ghost of Deleted Items: Understanding setIsRecyclable(false) in RecyclerView
Have you ever encountered a situation where you delete an item from a RecyclerView, but its ghost remains in the background, haunting your UI? This frustrating behavior can occur when you call setIsRecyclable(false) on the ViewHolder of the deleted item. Let's dive into why this happens and how to avoid it.
The Scenario
Imagine you have a RecyclerView displaying a list of items. When a user clicks the "Delete" button, you remove the corresponding item from the underlying data source and notify the RecyclerView to update using notifyItemRemoved(). However, instead of smoothly fading away, the deleted item remains visible in the background, creating a jarring visual glitch.
The Code
Here's a simplified example:
// ViewHolder class
public class MyViewHolder extends RecyclerView.ViewHolder {
// ...
public MyViewHolder(View itemView) {
super(itemView);
// ...
itemView.setOnClickListener(view -> {
// Delete item from data source
// ...
notifyItemRemoved(getAdapterPosition());
});
itemView.setOnLongClickListener(view -> {
// Mark item as non-recyclable
setIsRecyclable(false);
return true;
});
}
// ...
}
In this code, the setOnLongClickListener sets the ViewHolder as non-recyclable. Let's understand why this causes the problem.
The Problem:
-
RecyclerView's Recycling Mechanism:
RecyclerViewis designed for efficient item rendering. It reuses existingViewHoldersto display new data, saving resources. When an item is removed, theViewHolderassociated with it is not immediately destroyed. Instead, it's placed in a pool of availableViewHoldersfor potential reuse. -
setIsRecyclable(false): By callingsetIsRecyclable(false), you prevent theViewHolderfrom being recycled. This means that even after the item is deleted, theViewHolderremains in the background, ready to be used for a new item.
Why Does the Ghost Appear?
When a new item is displayed, the RecyclerView might reuse the ViewHolder of the deleted item. Since the ViewHolder still holds the old view elements, it appears as a ghost behind the new item. This happens because the ViewHolder retains its original state, even though the data it should be displaying is removed.
The Solution
To avoid this ghosting effect, there are two primary approaches:
-
Don't Mark Deleted ViewHolders as Non-Recyclable: The most straightforward solution is to remove the line
setIsRecyclable(false)from yourViewHolder. This allows theRecyclerViewto recycle theViewHolderas intended, ensuring smooth removal of items. -
Clean Up the View Before Recyclability: If you need to disable recycling for specific reasons, ensure you properly clean up the view within the
ViewHolderbefore it's potentially reused. This could involve:- Setting visibility to
GONE: Hiding the view elements of the deleted item. - Resetting view properties: Resetting any view properties that might cause conflicts with the new data.
- Releasing resources: Releasing any held resources like bitmaps or other expensive data.
- Setting visibility to
Example:
// ViewHolder class
public class MyViewHolder extends RecyclerView.ViewHolder {
// ...
public MyViewHolder(View itemView) {
super(itemView);
// ...
itemView.setOnLongClickListener(view -> {
// Mark item as non-recyclable (optional)
// setIsRecyclable(false); // Remove this line
// ...
itemView.setVisibility(View.GONE); // Clean up view
return true;
});
}
// ...
}
Remember: While setIsRecyclable(false) might be tempting for specific use cases, it can lead to unwanted visual glitches. Prioritize recycling by removing the call to setIsRecyclable(false) or by cleaning up the view properly when the item is removed.
This article provides you with a better understanding of how the RecyclerView recycling mechanism works and why setIsRecyclable(false) can lead to visual inconsistencies. By following the suggested solutions, you can avoid the haunting ghost of deleted items and ensure a smoother user experience.
