Android最便捷banner轮播图实现原理及代码

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原理图：
这里写图片描述
代码实现
public class CyclerViewPager extends ViewPager {    public CyclerViewPager(Context context) {        super(context);    }    public CyclerViewPager(Context context, AttributeSet attrs) {        super(context, attrs);    }    @Override    public void addOnPageChangeListener(OnPageChangeListener listener) {        MyPageChangeListener myPageChangeListener = new MyPageChangeListener(listener);        super.addOnPageChangeListener(myPageChangeListener);    }    @Override    public void setAdapter(PagerAdapter adapter) {        //  修正  adapter 中position        MyAdapter myAdapter = new MyAdapter(adapter);        addOnPageChangeListener(null); //手动增加一个监听        super.setAdapter(myAdapter);        setCurrentItem(1);        //开启自动轮播        startScroll();//自动轮播    }    @Override    public boolean onTouchEvent(MotionEvent ev) {        //手指触摸  按下 停止轮播  抬起继续轮播        switch (ev.getAction()){            case MotionEvent.ACTION_DOWN:                stopScroll();                break;            case MotionEvent.ACTION_MOVE:                break;            case MotionEvent.ACTION_CANCEL://取消事件            case MotionEvent.ACTION_UP:                startScroll();                break;        }        return super.onTouchEvent(ev);    }    Handler handler = new Handler(){        @Override        public void handleMessage(Message msg) {            super.handleMessage(msg);            int currentItem = getCurrentItem();            currentItem ++;            setCurrentItem(currentItem);            handler.sendEmptyMessageDelayed(1, 4000);//4s发送消息        }    };    public void startScroll() {        //开启轮播        handler.sendEmptyMessageDelayed(1, 4000);//4s发送消息    }    public void stopScroll(){        handler.removeMessages(1);    }    public class MyPageChangeListener implements OnPageChangeListener {        private OnPageChangeListener listener;        private int position;        public MyPageChangeListener(OnPageChangeListener listener) {            this.listener = listener;        }        @Override        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {            if (listener != null)                listener.onPageScrolled(position, positionOffset, positionOffsetPixels);        }        @Override        public void onPageSelected(int position) {            this.position = position;            if (listener != null)                listener.onPageSelected(position);        }        @Override        public void onPageScrollStateChanged(int state) {            //状态改变的时候 调用    手指抬起的时候切换            if (state == ViewPager.SCROLL_STATE_IDLE) {                //空闲切换                // 页面切换   自动的切换到对应的界面    最后一个A----->第一个A                if (position == getAdapter().getCount() - 1) {                    //最后一个元素  是否平滑切换                    setCurrentItem(1, false);                } else if (position == 0) {                    //是第一个元素{D] ----> 倒数第二个元素[D]                    setCurrentItem(getAdapter().getCount() - 2, false);                }            }            if (listener != null)                listener.onPageScrollStateChanged(state);        }    }    public class MyAdapter extends PagerAdapter {        private PagerAdapter adapter;        public MyAdapter(PagerAdapter adapter) {            this.adapter = adapter;  //[ABCD]        }        @Override        public Object instantiateItem(ViewGroup container, int position) {            //  position 已经是 [DABCDA] 的索引了            // 修正后的索引 应该是 [ABCD]的索引            //修正position            if (position == 0) { //新增的D                position = adapter.getCount() - 1;// 最后一个元素            } else if (position == getCount() - 1) {  //最后一个元素 A                position = 0;            } else {                position -= 1; //计算新的索引            }            return adapter.instantiateItem(container, position);        }        @Override        public void destroyItem(ViewGroup container, int position, Object object) {            adapter.destroyItem(container, position, object);        }        @Override        public int getCount() {            return adapter.getCount() + 2;        }        @Override        public boolean isViewFromObject(View view, Object object) {            return adapter.isViewFromObject(view, object);        }    }}
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