滑动页面添加页面指示符号

在android中应用ViewPager显示多页面时，在页面下面可以设置一排多个小圆点以指示当前多少个页面以及当前处于第几个页面。
1,在布局文件中

<androidx.viewpager.widget.ViewPager
            android:id="@+id/eric_viewpager"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_gravity="center"
            />
<LinearLayout
            android:id="@+id/eric_indicator_layout"
            android:layout_width="@dimen/size_100dp"
            android:layout_height="wrap_content"
            android:layout_gravity="bottom|center_vertical"
            android:gravity="center_horizontal"
            android:layout_marginBottom="@dimen/size_80dp"
            android:orientation="horizontal"
            />

2,在源文件EricActivity.java中

private ViewPager viewPager;
private LinearLayout indicatorLayout;
viewPager = findViewById(R.id.eric_viewpager);
indicatorLayout = findViewById(R.id.eric_indicator_layout);
List<View> views = new ArrayList<>();
views.add(new EricView());
EricViewAdapter adapter = new EricViewAdapter(context, views);
viewPager.setAdapter(adapter);
viewPager.addOnPageChangeListener(pageChangeListener);
setIndicator();

private final ViewPager.OnPageChangeListener pageChangeListener = new ViewPager.OnPageChangeListener() {
        @Override
        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
        }

        @Override
        public void onPageSelected(int position) {
            setIndicatorSelected(position);
        }

        @Override
        public void onPageScrollStateChanged(int state) {
        }
    };
	
private void setIndicatorSelected(int position) {
        for (int i = 0; i < indicatorLayout.getChildCount(); i++) {
            ImageView dot = (ImageView) indicatorLayout.getChildAt(i);
            if (i == position) {
                dot.setImageResource(R.drawable.eric_indicator_selected);
            } else {
                dot.setImageResource(R.drawable.eric_indicator_unselected);
            }
        }
    }
	
private void setIndicator() {
        int pageCount = Objects.requireNonNull(viewPager.getAdapter()).getCount();
        for (int i = 0; i < pageCount; i++) {
            ImageView dot = new ImageView(EricActivity.this);
            dot.setImageResource(R.drawable.eric_indicator_selected);
            LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(
                    LinearLayout.LayoutParams.WRAP_CONTENT,
                    LinearLayout.LayoutParams.WRAP_CONTENT,
                    1.0F
            );
            dot.setLayoutParams(params);
            dot.setTag(i);
            indicatorLayout.addView(dot);
        }
        setIndicatorSelected(0);
    }

3,定义Adapter

import androidx.viewpager.widget.PagerAdapter;
public class EricViewAdapter extends PagerAdapter {
    private Context mContext;
    private List<View> mViews;

    public EricViewAdapter(Context context, List<View> views) {
        mContext = context;
        mViews = views;
    }

    @Override
    public int getCount() {
        return mViews.size();
    }

    @Override
    public boolean isViewFromObject(@NonNull View view, @NonNull Object object) {
        return view == object;
    }

    @NonNull
    @Override
    public Object instantiateItem(@NonNull ViewGroup container, int position) {
        View view = mViews.get(position);
        container.addView(view);
        return view;
    }

    @Override
    public void destroyItem(@NonNull ViewGroup container, int position, @NonNull Object object) {
        container.removeView((View)object);
    }
}