自定义ViewPager和RecyclerView指示器 Indicator

现在好多App首页都会有这样的条目

这种的实现方式要么是viewpager翻页滚动，要么就是recyclerView持续滚动。下面的指示器系统的太丑 ，所以就自定义了一个。下面是demo简单的效果图：

ViewPagerIndicator

因为嫌麻烦这里的指示器没有用Canvas进行绘制，用了布局文件代替：

指示器布局文件 view_indicator.xml

ViewPagerIndicator.java

public class ViewPagerIndicator extends FrameLayout {

    private View rootView;
    private View indView;

    public ViewPagerIndicator(@NonNull Context context) {
        this(context, null);
    }

    public ViewPagerIndicator(@NonNull Context context, @Nullable AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public ViewPagerIndicator(@NonNull Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        View root = inflate(context, R.layout.app_viewpager_indicator, this);
        rootView = root.findViewById(R.id.root);
        indView = root.findViewById(R.id.ind_view);
    }

    int indViewWidth = 0;

    @Override
    public void draw(Canvas canvas) {
        super.draw(canvas);
    }

    public void setWithViewPager(ViewPager viewPager) {
        //如果没有adapter，则隐藏不显示
        if (null == viewPager.getAdapter()) {
            setVisibility(GONE);
            Log.e(getClass().getSimpleName(), "no adapter");
            return;
        }
        //获取viewPager中fragment的数量
        final int count = viewPager.getAdapter().getCount();
        if (count == 0) {
            return;
        }

        //加载到window之后再进行view宽度的获取
        rootView.post(new Runnable() {
            @Override
            public void run() {
                //获取当前滑块的宽度
                indViewWidth = getWidth() / count;
                FrameLayout.LayoutParams layoutParams = (FrameLayout.LayoutParams) indView.getLayoutParams();
                layoutParams.width = indViewWidth;
                indView.setLayoutParams(layoutParams);
            }
        });

        viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            /**
             *
             * @param position
             * @param positionOffset [0，1]中的值，指示在位置处与页面的偏移百分比。
             * @param positionOffsetPixels 以像素为单位的值，表示与位置的偏移量。
             */
            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
                //获取滑块距父布局左侧的距离
                int left = (int) (position * indViewWidth + positionOffset * indViewWidth);

                //重新布局滑块view
                indView.layout(left, indView.getTop(), left + indViewWidth, indView.getBottom());
            }

            @Override
            public void onPageSelected(int position) {

            }

            @Override
            public void onPageScrollStateChanged(int state) {

            }
        });
    }
}

步骤如下
1.计算出滑块的宽高
2.为viewPager添加滑动监听事件，监听滑动距离，计算出移动距离重新布局滑块

RecyclerViewIndicator

indicator 布局同上

RecyclerViewIndicator.java

public class RecyclerViewIndicator extends FrameLayout {

    private View rootView;
    private View indView;

    public RecyclerViewIndicator(@NonNull Context context) {
        this(context, null);
    }

    public RecyclerViewIndicator(@NonNull Context context, @Nullable AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public RecyclerViewIndicator(@NonNull Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        View root = inflate(context, R.layout.app_viewpager_indicator, this);
        rootView = root.findViewById(R.id.root);
        indView = root.findViewById(R.id.ind_view);
    }

    int indViewWidth = 0;
    int indViewHeight = 0;
    float rate = 0f;

    /**
     * 绑定recyclerView
     * @param recyclerView
     * @param orientation 排列方向
     *
     *  这里用到的recyclerView的三个方法
     *  computeHorizontalScrollExtent/computeVerticalScrollExtent 当前显示在屏幕上的总长度
     *  computeHorizontalScrollOffset/computeVerticalScrollOffset 当前滑动的总长度
     *  computeHorizontalScrollRange/computeVerticalScrollRange recylerView内部的总长度
     */
    public void setWithRecyclerView(final RecyclerView recyclerView, int orientation) {
        final boolean isHorizontal = orientation == RecyclerView.HORIZONTAL;
        rootView.post(new Runnable() {
            @Override
            public void run() {
                float scrollRange = isHorizontal ? recyclerView.computeHorizontalScrollRange() : recyclerView.computeVerticalScrollRange();
                float scrollExtent = isHorizontal ? recyclerView.computeHorizontalScrollExtent() : recyclerView.computeVerticalScrollExtent();
                LayoutParams layoutParams = (LayoutParams) indView.getLayoutParams();

                if (isHorizontal) {
                    //算出比例
                    rate = (float) getWidth() / scrollRange;
                    //由显示在屏幕上的总长度算出滑块长度
                    indViewWidth = (int) (scrollExtent * rate);
                    layoutParams.height = LayoutParams.MATCH_PARENT;
                    layoutParams.width = indViewWidth;
                } else {
                    rate = (float) getHeight() / scrollRange;
                    layoutParams.width = LayoutParams.MATCH_PARENT;
                    indViewHeight = (int) (scrollExtent * rate);
                    layoutParams.height = indViewHeight;
                }
                indView.setLayoutParams(layoutParams);
            }
        });

        recyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
            @Override
            public void onScrolled(@NonNull RecyclerView recyclerView, int dx, int dy) {
                super.onScrolled(recyclerView, dx, dy);
                int scrollOffset = isHorizontal ? recyclerView.computeHorizontalScrollOffset() : recyclerView.computeVerticalScrollOffset();
                //由recyclerView滑动距离算出滑块移动距咯
                if (isHorizontal) {
                    int left = (int) (scrollOffset * rate);
                    indView.layout(left, indView.getTop(), left + indViewWidth, indView.getBottom());
                } else {
                    int top = (int) (scrollOffset * rate);
                    indView.layout(indView.getLeft(), top, indView.getRight(), top + indViewHeight);
                }

            }
        });
    }
}

步骤基本上和recyclerView的实现步骤一致，
这里主要用到了recyclerView的三个方法进行计算

computeHorizontalScrollExtent/computeVerticalScrollExtent 当前显示在屏幕上的总长度
computeHorizontalScrollOffset/computeVerticalScrollOffset 当前滑动的总长度
computeHorizontalScrollRange/computeVerticalScrollRange recylerView内部的总长度

通过 orientation 来区分recyclrView 的排列方式

demo地址

demo只是做了实现的方式，界面有点丑，自己可以更改背景进行修改。也可以是用绘制的方式，添加自定义view的参数。