Android RecyclerView 水平滑动设置Item间距，首个Item距左边20

您可以通过设置RecyclerView的LayoutManager来实现水平滑动和设置item间距。首先，创建一个自定义的ItemDecoration类来设置item间距：

public class HorizontalSpaceItemDecoration extends RecyclerView.ItemDecoration {
    private final int horizontalSpaceHeight;

    public HorizontalSpaceItemDecoration(int horizontalSpaceHeight) {
        this.horizontalSpaceHeight = horizontalSpaceHeight;
    }

    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
        outRect.left = horizontalSpaceHeight;
        if (parent.getChildAdapterPosition(view) == 0) {
            outRect.left = horizontalSpaceHeight * 2; // 设置首个item距左边的距离为20
        }
        outRect.right = horizontalSpaceHeight;
    }
}

然后，在您的Activity或Fragment中，进行如下设置：

RecyclerView recyclerView = findViewById(R.id.recyclerView);
recyclerView.setLayoutManager(new LinearLayoutManager(this, LinearLayoutManager.HORIZONTAL, false));
recyclerView.addItemDecoration(new HorizontalSpaceItemDecoration(10));

这样，您的RecyclerView将以水平滑动的方式展示，并且每个item之间的间距为10，首个item距离左边的距离为20。