嵌套FrameLayout后RecyclerView的onBind异常，Item交替着色失效

Hey there! Let's dig into exactly what's happening under the hood when you add a FrameLayout to your RecyclerView item layout, and why that's throwing off your alternating color pattern.

First, the Technical Changes Introduced by FrameLayout #

When you wrap your original item layout in a FrameLayout, three key shifts impact RecyclerView's onBindViewHolder behavior:

1. Root Layout Identity Swap
   Your RecyclerView's ViewHolder.itemView now points to the FrameLayout instead of your original root view (like a LinearLayout). If your existing code was targeting the old root view to set background colors, you're no longer modifying the actual top-level container that RecyclerView uses as the item's base.

2. Drawing Layer Priority
   FrameLayout draws its own background first, then renders child views on top. If you only set the background color on the child view (your original layout), the FrameLayout's background— which might retain old colors from recycled views— will show through. This is especially noticeable if the child view doesn't fully fill the FrameLayout's bounds.

3. Unreset View State During Reuse
   RecyclerView reuses ViewHolders to optimize performance. When a ViewHolder is recycled, it only resets properties you explicitly modify in onBindViewHolder. If you don't update the FrameLayout's background color during binding, it will keep the color from the last item it displayed, leading to inconsistent, glitchy coloring.

Common Scenario That Causes the Glitch #

Let's say your original setup was:

• Item layout root: LinearLayout with ID item_root
• In onBindViewHolder, you did:

  holder.itemRoot.setBackgroundColor(if (position % 2 == 0) Color.WHITE else Color.GRAY)
  

After adding FrameLayout:

• New root is FrameLayout (no ID), with your original LinearLayout as a child
• If you still target item_root to set colors, the FrameLayout's background remains untouched. When RecyclerView reuses this ViewHolder for a new position, the FrameLayout might still have the gray color from a previous odd-position item, while the child LinearLayout is set to white— resulting in a mixed or incorrect color display.

Fixes to Get Your Alternating Colors Back #

• Target the new root layout: Update your ViewHolder to reference the FrameLayout (or just use holder.itemView, since that's the root) and set the background color directly on it:

  holder.itemView.setBackgroundColor(if (position % 2 == 0) Color.WHITE else Color.GRAY)
  

• Ensure full coverage: If you need to keep setting colors on the child view, make sure the child view fills the FrameLayout completely (use match_parent for width/height) and explicitly set the FrameLayout's background to a default color (like transparent or your base color) in the layout XML or onBindViewHolder.
• Double-check ViewHolder references: Verify that your ViewHolder is caching the correct views and that you're modifying the right elements during binding.

内容的提问来源于stack exchange，提问作者ShankPossible