RecyclerView列表項背景漸變效果

要實現RecyclerView列表項背景的漸變效果，可以通過定義一個自定義的ItemDecoration來實現。以下是一個示例代碼：

public class GradientItemDecoration extends RecyclerView.ItemDecoration {
    
    private int startColor;
    private int endColor;
    
    public GradientItemDecoration(int startColor, int endColor) {
        this.startColor = startColor;
        this.endColor = endColor;
    }
    
    @Override
    public void onDraw(@NonNull Canvas c, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
        LinearLayoutManager layoutManager = (LinearLayoutManager) parent.getLayoutManager();
        
        int childCount = parent.getChildCount();
        int width = parent.getWidth();
        
        for (int i = 0; i < childCount; i++) {
            View child = parent.getChildAt(i);
            int position = parent.getChildAdapterPosition(child);
            float alpha = 1 - Math.abs(layoutManager.getDecoratedLeft(child)) / (float) width;
            int color = interpolateColor(startColor, endColor, alpha);
            
            Paint paint = new Paint();
            paint.setColor(color);
            c.drawRect(child.getLeft(), child.getTop(), child.getRight(), child.getBottom(), paint);
        }
    }
    
    private int interpolateColor(int startColor, int endColor, float ratio) {
        float inverseRatio = 1f - ratio;
        
        int startA = (startColor >> 24) & 0xff;
        int startR = (startColor >> 16) & 0xff;
        int startG = (startColor >> 8) & 0xff;
        int startB = startColor & 0xff;
        
        int endA = (endColor >> 24) & 0xff;
        int endR = (endColor >> 16) & 0xff;
        int endG = (endColor >> 8) & 0xff;
        int endB = endColor & 0xff;
        
        int a = (int) (startA * inverseRatio + endA * ratio);
        int r = (int) (startR * inverseRatio + endR * ratio);
        int g = (int) (startG * inverseRatio + endG * ratio);
        int b = (int) (startB * inverseRatio + endB * ratio);
        
        return Color.argb(a, r, g, b);
    }
}

使用方法如下：

GradientItemDecoration itemDecoration = new GradientItemDecoration(Color.parseColor("#FF0000"), Color.parseColor("#00FF00"));
recyclerView.addItemDecoration(itemDecoration);

在這個示例中，我們定義了一個漸變的ItemDecoration，并在RecyclerView中應用該ItemDecoration，從而實現了RecyclerView列表項背景的漸變效果。您可以根據自己的需求定義不同的漸變效果和顏色。