Question

我正在为.hexagon:before { position: absolute; top: 0; left: 50%; background-color: inherit; height: inherit; width: 100%; content: ''; transform: rotate(60deg); transform-origin: 25% 25%; } .hexagon:after { position: absolute; top: 0; left: 50%; background-color: inherit; height: inherit; width: 100%; content: ''; transform: rotate(-60deg); transform-origin: 25% 75%; } .hexagon-wrapper:first-child .hexagon { background-color: #D93; transform: translateZ(100px); } .hexagon-wrapper:nth-child(2) .hexagon { background-color: #6C6; transform: translateZ(0); }使用水平布局管理器。我需要以下面的方式制作RecyclerView：点击某个项目时 - 将smoothScrool置于该位置并将该项目放在RecyclerView的中心（如果可能，例如20中的10项）。< / p>

所以，我对RecyclerView没有问题，但是如何把项目放在smoothScrollToPosition()的中心???

谢谢！

Answer 1

是的，这是可能的。

实施RecyclerView.SmoothScroller方法onTargetFound(View, State, Action)。

/**
 * Called when the target position is laid out. This is the last callback SmoothScroller
 * will receive and it should update the provided {@link Action} to define the scroll
 * details towards the target view.
 * @param targetView    The view element which render the target position.
 * @param state         Transient state of RecyclerView
 * @param action        Action instance that you should update to define final scroll action
 *                      towards the targetView
 */
abstract protected void onTargetFound(View targetView, State state, Action action);

具体在LinearLayoutManager LinearSmoothScroller：

public class CenterLayoutManager extends LinearLayoutManager {

    public CenterLayoutManager(Context context) {
        super(context);
    }

    public CenterLayoutManager(Context context, int orientation, boolean reverseLayout) {
        super(context, orientation, reverseLayout);
    }

    public CenterLayoutManager(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
        super(context, attrs, defStyleAttr, defStyleRes);
    }

    @Override
    public void smoothScrollToPosition(RecyclerView recyclerView, RecyclerView.State state, int position) {
        RecyclerView.SmoothScroller smoothScroller = new CenterSmoothScroller(recyclerView.getContext());
        smoothScroller.setTargetPosition(position);
        startSmoothScroll(smoothScroller);
    }

    private static class CenterSmoothScroller extends LinearSmoothScroller {

        CenterSmoothScroller(Context context) {
            super(context);
        }

        @Override
        public int calculateDtToFit(int viewStart, int viewEnd, int boxStart, int boxEnd, int snapPreference) {
            return (boxStart + (boxEnd - boxStart) / 2) - (viewStart + (viewEnd - viewStart) / 2);
        }
    }
}

Answer 2

答案的改进-无需覆盖LinearLayoutManager

根据上一个答案：

public class CenterSmoothScroller extends LinearSmoothScroller {

    CenterSmoothScroller(Context context) {
        super(context);
    }

    @Override
    public int calculateDtToFit(int viewStart, int viewEnd, int boxStart, int boxEnd, int snapPreference) {
        return (boxStart + (boxEnd - boxStart) / 2) - (viewStart + (viewEnd - viewStart) / 2);
    }
}

如何使用它：

RecyclerView.LayoutManager lm = new GridLayoutManager(...): // or whatever layout manager you need

...

RecyclerView.SmoothScroller smoothScroller = new CenterSmoothScroller(recyclerView.getContext());

smoothScroller.setTargetPosition(position);

lm.startSmoothScroll(smoothScroller);

Answer 3

以防万一，在接受的答案中需要班级的等同于科特林的人。

class CenterLayoutManager : LinearLayoutManager {
    constructor(context: Context) : super(context)
    constructor(context: Context, orientation: Int, reverseLayout: Boolean) : super(context, orientation, reverseLayout)
    constructor(context: Context, attrs: AttributeSet, defStyleAttr: Int, defStyleRes: Int) : super(context, attrs, defStyleAttr, defStyleRes)

    override fun smoothScrollToPosition(recyclerView: RecyclerView, state: RecyclerView.State, position: Int) {
        val centerSmoothScroller = CenterSmoothScroller(recyclerView.context)
        centerSmoothScroller.targetPosition = position
        startSmoothScroll(centerSmoothScroller)
    }

    private class CenterSmoothScroller(context: Context) : LinearSmoothScroller(context) {
        override fun calculateDtToFit(viewStart: Int, viewEnd: Int, boxStart: Int, boxEnd: Int, snapPreference: Int): Int = (boxStart + (boxEnd - boxStart) / 2) - (viewStart + (viewEnd - viewStart) / 2)
    }
}

Answer 4

从现在（2019年2月）开始，我可以在ListView中轻松使用此代码

(ListView)word_list_view.smoothScrollToPositionFromTop(your_item_index, center_position.y);

RecyclerView尚未验证，我想也是一样。

Answer 5

基于@Boda 的回答，如果您想控制平滑滚动速度（以获得更好的动画效果），您可以使用以下方法：

class CenterLayoutManager : LinearLayoutManager {
    constructor(context: Context) : super(context)
    constructor(context: Context, orientation: Int, reverseLayout: Boolean) : super(
        context,
        orientation,
        reverseLayout
    )

    constructor(context: Context, attrs: AttributeSet, defStyleAttr: Int, defStyleRes: Int) : super(
        context,
        attrs,
        defStyleAttr,
        defStyleRes
    )

    override fun smoothScrollToPosition(
        recyclerView: RecyclerView,
        state: RecyclerView.State,
        position: Int
    ) {
        val centerSmoothScroller = CenterSmoothScroller(recyclerView.context)
        centerSmoothScroller.targetPosition = position
        startSmoothScroll(centerSmoothScroller)
    }

    private class CenterSmoothScroller(context: Context) : LinearSmoothScroller(context) {
        override fun calculateDtToFit(
            viewStart: Int,
            viewEnd: Int,
            boxStart: Int,
            boxEnd: Int,
            snapPreference: Int
        ): Int = (boxStart + (boxEnd - boxStart) / 2) - (viewStart + (viewEnd - viewStart) / 2)

        override fun calculateSpeedPerPixel(displayMetrics: DisplayMetrics): Float {
            return MILLISECONDS_PER_INCH / displayMetrics.densityDpi
        }
    }

    companion object {
        // This number controls the speed of smooth scroll
        private const val MILLISECONDS_PER_INCH = 150f
    }
}

用法：

recyclerView.layoutManager = CenterLayoutManager(requireContext(), LinearLayoutManager.HORIZONTAL, false)
recyclerView.smoothScrollToPosition(selectedPosition)

Answer 6

对我来说这种方法有效：

recyclerView.smoothScrollToPosition(desiredPostion);

RecyclerView smoothScroll位于中心位置。安卓

6 个答案: