Android Horizo​​ntal Snapping可滚动RecyclerView

Question

我的问题有解决方案吗？

我目前正在使用SnapHelper但结果是这样的。

Snapping RecyclerView

如您所见，滚动视图无法在第一个项目中停止，但滚动时其他项目已经能够居中对焦。如何实现每个项目的中心焦点？

代码：

public class ScrollingSnap1 extends AppCompatActivity {
    private ArrayList<String> arraylist = new ArrayList<>();
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_scrolling_snap1);
        arraylist.add("1111111111111111111111111111111111111111");
        arraylist.add("2222222222222222222222222");
        arraylist.add("3333333333333333333333333333333333333333333333333");
        arraylist.add("99999999");
        arraylist.add("1010101010101001010101010");
        Adapter1 adapter1 = new Adapter1(arraylist);
        RecyclerView recyclerview = (RecyclerView)findViewById(R.id.recycler2);
        SnapHelper snapHelper = new LinearSnapHelper();
        recyclerview.setLayoutManager(new LinearLayoutManager(this, LinearLayoutManager.HORIZONTAL, true));
        recyclerview.setAdapter(adapter1);
        snapHelper.attachToRecyclerView(recyclerview);
    }
}

Answer 1

为了使第一个和最后一个项目居中，您需要在RecyclerView的开头和结尾处创建额外的空间。一种简单的方法是使用ItemDecoration，如下所示：

class BoundsOffsetDecoration : ItemDecoration() {
    override fun getItemOffsets(outRect: Rect,
                                view: View,
                                parent: RecyclerView,
                                state: RecyclerView.State) {
        super.getItemOffsets(outRect, view, parent, state)

        val itemPosition = parent.getChildAdapterPosition(view)

        // It is crucial to refer to layoutParams.width (view.width is 0 at this time)!
        val itemWidth = view.layoutParams.width
        val offset = (parent.width - itemWidth) / 2

        if (itemPosition == 0) {
            outRect.left = offset
        } else if (itemPosition == state.itemCount - 1) {
            outRect.right = offset
        }
    }
}