新手导航页（小圆点

让小红点随滑动的距离而移动（有动画效果），利用ViewPager的监听事件setOnPageChangeListener来实现

//注意测量小圆点边距时要layout完才能测量，否则为0（自定义View的三个过程）

public class GuideActivity extends AppCompatActivity {

    private ViewPager mViewPager;

    private ArrayList<ImageView> mImageViews;//ImageView集合

    //引导图片id数组
    private int[] mImageIds = new int[]{R.drawable.guide_1, R.drawable.guide_2, R.drawable.guide_3};
    private LinearLayout llContainer;
    private ImageView ivRedPoint;
    private int mPointDis; //两个小红点之间的距离
    private Button btnStart;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_NO_TITLE);//去除标题栏
        setContentView(R.layout.activity_guide);

        mViewPager = (ViewPager) findViewById(R.id.vp_guide);
        llContainer = (LinearLayout) findViewById(R.id.ll_container);
        ivRedPoint = (ImageView) findViewById(R.id.iv_red_point);
        btnStart = (Button) findViewById(R.id.btn_start);
        initData();
        mViewPager.setAdapter(new GuideAdapter());//设置数据

        mViewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
                //当页面滑动过程中的回调
                System.out.println("当前位置：" + position + ";移动偏移百分比：" + positionOffset);
                
                //更新小红点距离
                int leftMargin = (int) (mPointDis * positionOffset) + position * mPointDis;//计算当前小红点的左边距

                RelativeLayout.LayoutParams params = (RelativeLayout.LayoutParams) ivRedPoint.getLayoutParams();
                params.leftMargin = leftMargin;//修改左边距
                
                //重新设置布局参数
                ivRedPoint.setLayoutParams(params);
            }

            @Override
            public void onPageSelected(int position) {
                //页面被选中
                if (position == mImageViews.size() - 1) {//最后一个显示按钮
                    btnStart.setVisibility(View.VISIBLE);
                } else {
                    btnStart.setVisibility(View.GONE);
                }
            }

            @Override
            public void onPageScrollStateChanged(int state) {
                //页面状态发生变化的回调
            }
        });
        //计算两个圆点的距离
        //移动距离=第二个圆点left值-第二个圆点left值
        //mPointDis = llContainer.getChildAt(1).getLeft() - llContainer.getChildAt(0).getLeft();
        //监听layout方法结束的事件，位置确定好后测量 view的绘制过程
        //视树图
        ivRedPoint.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
            @Override
            public void onGlobalLayout() {
                ivRedPoint.getViewTreeObserver().removeOnGlobalLayoutListener(this);
                
                //layout方法执行结束的回调
                mPointDis = llContainer.getChildAt(1).getLeft() - llContainer.getChildAt(0).getLeft();
                
            }
        });
        
    }

    //初始化数据
    private void initData() {
        mImageViews = new ArrayList<>();
        for (int i = 0; i < mImageIds.length; i++) {
            ImageView view = new ImageView(this);
            view.setBackgroundResource(mImageIds[i]);//通过设置背景，可以让宽高填充布局
            mImageViews.add(view);

            //初始化小圆点
            ImageView point = new ImageView(this);
            point.setImageResource(R.drawable.shape_point_gray);

            //设置布局参数，宽高充满布局
            LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(
                    LinearLayout.LayoutParams.WRAP_CONTENT,
                    LinearLayout.LayoutParams.WRAP_CONTENT);

            if (i > 0) {
                //从左边第二个开始
                params.leftMargin = 13;
            }
            point.setLayoutParams(params);
            llContainer.addView(point);//给容器添加圆点

        }
    }

    class GuideAdapter extends PagerAdapter {

        //item的个数
        @Override
        public int getCount() {
            return mImageViews.size();
        }

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

        //初始化item
        @Override
        public Object instantiateItem(ViewGroup container, int position) {
            ImageView view = mImageViews.get(position);
            container.addView(view);
            return view;
        }

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