Android:控制平滑滚动回收器视图

Question

我正在使用Recyclerview和CardView.我知道如何控制列表视图的速度.但不适用于Recyclerview.

我在找到的类名SmoothScroll中搜索了很多.怎么用？我不知道!现在,Recyclerview默认滚动速度很快.

更新:

我总结吉尔回答与此

Answer 1

当你说" smoothScroll" 时,你的意思还不清楚.你可能指的是smoothScrollToPosition自动滚动到指定位置的自动" ",你可能正在谈论手动滚动,你可能正在谈论投掷.为了繁荣,我现在将尝试回答所有这些问题.

1.自动平滑滚动.

在布局管理器中,您需要实现该smoothScrollToPosition方法:

    @Override
    public void smoothScrollToPosition(RecyclerView recyclerView, State state, int position)
    {
        // A good idea would be to create this instance in some initialization method, and just set the target position in this method.
        LinearSmoothScroller smoothScroller = new LinearSmoothScroller(getContext())
        {
            @Override
            public PointF computeScrollVectorForPosition(int targetPosition)
            {
                int yDelta = calculateCurrentDistanceToPosition(targetPosition);
                return new PointF(0, yDelta);
            }

            // This is the important method. This code will return the amount of time it takes to scroll 1 pixel.
            // This code will request X milliseconds for every Y DP units.
            @Override
            protected float calculateSpeedPerPixel(DisplayMetrics displayMetrics)
            {
                return X / TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, Y, displayMetrics);
            }

        };
        smoothScroller.setTargetPosition(position);

        startSmoothScroll(smoothScroller);
    }

在这个例子中,我使用名为"calculateCurrentDistanceToPosition"的辅助方法.这可能有点棘手,因为它涉及跟踪当前滚动位置,以及计算给定y位置的滚动位置.您可以在此处找到如何跟踪回收器滚动的示例.

计算给定位置的滚动y实际上取决于您的回收器显示的内容.假设您的所有项目都是相同的高度,您可以通过执行以下计算来计算:

targetScrollY = targetPosition * itemHeight

然后,要计算您需要滚动的距离,只需使用目标滚动y减去当前滚动y:

private int calculateCurrentDistanceToPosition(int targetPosition) {
    int targetScrollY = targetPosition * itemHeight;
    return targetScrollY - currentScrollY;
}

2.减慢手动滚动.

再次,您需要编辑布局管理器,这次 - scrollVerticallyBy方法:

    @Override
    public int scrollVerticallyBy(int delta, Recycler recycler, State state)
    {
       // write your limiting logic here to prevent the delta from exceeding the limits of your list.

       int prevDelta = delta;
       if (getScrollState() == SCROLL_STATE_DRAGGING)
            delta = (int)(delta > 0 ? Math.max(delta * MANUAL_SCROLL_SLOW_RATIO, 1) : Math.min(delta * MANUAL_SCROLL_SLOW_RATIO, -1));  

       // MANUAL_SCROLL_SLOW_RATIO is between 0 (no manual scrolling) to 1 (normal speed) or more (faster speed).
       // write your scrolling logic code here whereby you move each view by the given delta

        if (getScrollState() == SCROLL_STATE_DRAGGING)
            delta = prevDelta;

        return delta;
    }

编辑:在上面的方法中,我调用" getScrollState()".这是一种方法RecyclerView.在此实现中,我的自定义LayoutManager是我的自定义的嵌套类RecyclerView.如果这对您不起作用,您可以尝试通过某种界面模式获取滚动状态.

3.减慢速度

在这里,您希望缩小投掷速度.您需要覆盖flingRecyclerView子类中的方法:

@Override
public boolean fling(int velocityX, int velocityY)
{
     velocityY *= FLING_SCALE_DOWN_FACTOR; // (between 0 for no fling, and 1 for normal fling, or more for faster fling).

     return super.fling(velocityX, velocityY);
}

由于您没有发布任何代码或提供有关您的设置的大量信息,因此我很难提供更具针对性的解决方案,但我希望这涵盖了大多数基础,并将帮助您找到最适合您的解决方案.

Answer 2

我只是简化了如何使用它来控制平滑滚动的答案.

创建类

import android.content.Context;
import android.support.v7.widget.RecyclerView;
import android.util.AttributeSet;

public class CustomRecyclerView extends RecyclerView {

    Context context;

    public CustomRecyclerView(Context context) {
        super(context);
        this.context = context;
    }

    public CustomRecyclerView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public CustomRecyclerView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }

    @Override
    public boolean fling(int velocityX, int velocityY) {

        velocityY *= 0.7;
        // velocityX *= 0.7; for Horizontal recycler view. comment velocityY line not require for Horizontal Mode.

        return super.fling(velocityX, velocityY);
    }

}

通过将0.7替换为您的值来调整速度.

现在在这样的XML中使用这个类.

<<yourpackage>.CustomRecyclerView
    android:id="@+id/my_recycler_view"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:scrollbars="vertical" />

阅读Java中的RecyclerView.

CustomRecyclerView mRecyclerView;
mRecyclerView = (CustomRecyclerView) findViewById(R.id.my_recycler_view);

Answer 3

只需实现LinearLayoutManager的smoothScrollToPosition():

LinearLayoutManager layoutManager = new LinearLayoutManager(this) {

    @Override
    public void smoothScrollToPosition(RecyclerView recyclerView, RecyclerView.State state, int position) {
        LinearSmoothScroller smoothScroller = new LinearSmoothScroller(this) {

            private static final float SPEED = 300f;// Change this value (default=25f)

            @Override
            protected float calculateSpeedPerPixel(DisplayMetrics displayMetrics) {
                return SPEED / displayMetrics.densityDpi;
            }

        };
        smoothScroller.setTargetPosition(position);
        startSmoothScroll(smoothScroller);
    }

};