java – 从中​​心项目启动我的RecyclerView Horizo​​ntal Carousel

我正在创建一个旋转木马Horizo​​ntal RecyclerView,它具有从RecyclerView的第一项开始的焦点项目.

自定义CenterZoomLayoutManager的代码：

public class CenterZoomLayoutManager extends LinearLayoutManager {
private final float mShrinkAmount = 0.15f;
private final float mShrinkDistance = 0.9f;

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

@Override
public int scrollHorizontallyBy(int dx, RecyclerView.Recycler recycler, RecyclerView.State state) {
    int orientation = getOrientation();
    if (orientation == HORIZONTAL) {

        int scrolled = super.scrollHorizontallyBy(dx, recycler, state);
        float midpoint = getWidth() / 2.f;
        float d0 = 0.f;
        float d1 = mShrinkDistance * midpoint;
        float s0 = 1.f;
        float s1 = 1.f - mShrinkAmount;
        for (int i = 0; i < getChildCount(); i++) {
            View child = getChildAt(i);
            float childMidpoint =
                    (getDecoratedRight(child) + getDecoratedLeft(child)) / 2.f;
            float d = Math.min(d1, Math.abs(midpoint - childMidpoint));
            float scale = s0 + (s1 - s0) * (d - d0) / (d1 - d0);
            child.setScaleX(scale);
            child.setScaleY(scale);
        }
        return scrolled;
    } else return 0;
}

@Override
public void onLayoutChildren(RecyclerView.Recycler recycler, RecyclerView.State state) {
    super.onLayoutChildren(recycler, state);
    scrollHorizontallyBy(0, recycler, state);
}
}

在我的片段中,我有以下内容：

private void onSetRecyclerView() {

    recyclerView = fragmentView.findViewById(R.id.recyclerView);

    if (recyclerView != null) {
        RecyclerView.LayoutManager layoutManager = new CenterZoomLayoutManager(context, LinearLayoutManager.HORIZONTAL,
                false);

        recyclerView.scrollToPosition(storeList.size() / 2);

        final SnapHelper snapHelper = new LinearSnapHelper();
        snapHelper.attachToRecyclerView(recyclerView);
        recyclerView.setLayoutManager(layoutManager);
        recyclerView.setAdapter(adapter);
    }
}

我想从中心项目而不是从起始位置开始我的RecyclerView.

罪魁祸首：
在我的CenterZoomLayoutManager中,我通过scrollHorizo​​ntallyBy(0,recycleler,state)将像素偏移量设置为0像素.

问题：
我找不到将recyclerView.scrollToPosition(storeList.size()/ 2)创建的偏移像素传递给CenterZoomLayoutManager的方法.我试图寻找不同的内置方法来获得X-offset,但到目前为止还没有运气.

解决方法:

解决方案是更改LinearSnapHelper连接到RecyclerView的时间.以下是重新设计的onSetRecyclerView(),它将RecyclerView的中心项目捕捉到屏幕中心.请注意,在RecyclerView布局并适当滚动之前,不会连接LinearSnapHelper.您无需在onLayoutChildren()中进行任何滚动操作.

private void onSetRecyclerView() {
    recyclerView = findViewById(R.id.recyclerView);
    CenterZoomLayoutManager layoutManager =
        new CenterZoomLayoutManager(this, LinearLayoutManager.HORIZONTAL, false);
    recyclerView.setLayoutManager(layoutManager);
    recyclerView.setAdapter(adapter);
    // Scroll to the position we want to snap to
    layoutManager.scrollToPosition(storeList.size() / 2);
    // Wait until the RecyclerView is laid out.
    recyclerView.post(new Runnable() {
        @Override
        public void run() {
            // Shift the view to snap  near the center of the screen.
            // This does not have to be precise.
            int dx = (recyclerView.getWidth() - recyclerView.getChildAt(0).getWidth()) / 2;
            recyclerView.scrollBy(-dx, 0);
            // Assign the LinearSnapHelper that will initially snap the near-center view.
            LinearSnapHelper snapHelper = new LinearSnapHelper();
            snapHelper.attachToRecyclerView(recyclerView);
        }
    });
}

这是我的测试应用程序的初始屏幕显示的方式.有201家“商店”.

标签：android,java,android-recyclerview,android-scroll,linearlayoutmanager
来源： https://codeday.me/bug/20190827/1746278.html