web-dev-qa-db-ja.com

RecyclerView smoothScrollを中央に配置します。 android

RecyclerViewに水平レイアウトマネージャーを使用しています。次の方法でRecyclerViewを作成する必要があります。あるアイテムをクリックすると、smoothScroolをその位置に配置し、そのアイテムをRecyclerViewの中央に配置します(可能な場合、たとえば20から10アイテム) 。

したがって、smoothScrollToPosition()には問題ありませんが、RecyclerView ???の中心よりもアイテムを配置する方法は?

ありがとう!

24
Stan Malcolm

はい、可能です

_RecyclerView.SmoothScroller_のメソッドonTargetFound(View, State, Action)を実装することにより。

_/**
 * 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);
_

特にLinearLayoutManagerLinearSmoothScrollerで:

_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);
        }
    }
}
_
67
user3680200

答えの改善-LinearLayoutManagerをオーバーライドする必要はありません

前の回答から:

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);
    }
}

ここでそれを使用する方法:

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

...

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

smoothScroller.setTargetPosition(position);

lm.startSmoothScroll(smoothScroller);
17
user8944115

誰かが必要とする場合に備えて、受け入れられた答えのクラスのKotlinと同等が必要です。

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)
    }
}
1
Boda

今から(2019年2月)、ListViewでこのコードを簡単に使用できました

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

RecyclerViewは検証されていませんが、同じでしょう。

0
Corxit Sun