Android使用ViewPager做无限轮播，人为滑动时停止

曾经终败给现在 2022-07-14 04:42 175阅读 0赞

### 实现无限循环 ###

使用取模，获取到当前图片所在的位置。

private class MyPagerAdapter extends PagerAdapter { 
            private Context context;
            List<ImageView> list;
    
            public MyPagerAdapter(Context context, List<ImageView> list) {
                this.context = context;
                this.list = list;
            }
    
            @Override
            public int getCount() {
                //使用Integer的最大值，这样基本上就不需要滑动到最后了
                //除非用户很蛋疼
                return Integer.MAX_VALUE;
            }
    
            @Override
            public Object instantiateItem(ViewGroup container, int position) {
                //当前位置模上总数等于图片在数组中的位置
                position %= list.size();
                if (position < 0) {
                    position = list.size() + position;
                }
                ImageView imageView = list.get(position);
                //设置轮播点击事件
                final int finalPosition = position;
                imageView.setOnClickListener(new View.OnClickListener() {
                    @Override
                    public void onClick(View v) {
                        Intent intent = new Intent(getApplicationContext(), BannerActivity.class);
                        intent.putExtra("position", finalPosition);
                        startActivity(intent);
                    }
                });
                ViewGroup parent = (ViewGroup) imageView.getParent();
                if (parent != null) {
                    parent.removeView(imageView);
                }
                container.addView(imageView);
                return list.get(position);
            }
    
            @Override
            public boolean isViewFromObject(View view, Object object) {
                return object == view;
            }
    
            @Override
            public void destroyItem(ViewGroup container, int position, Object object) {
                //注意这里不要使用
                //container.removeView(list.get(position));
            }
        }

### 自动循环实现 ###

使用Handler每隔5秒一次消息，接收到轮播的动作就继续发一次消息，实现自动轮播的效果。

private class MyHandler extends Handler { 
            private Context context;
            //使用弱引用，避免handler造成内存泄露
            private WeakReference<MainActivity> weakReference;
    
            public MyHandler(WeakReference<MainActivity> weakReference) {
                this.weakReference = weakReference;
            }
    
    
            @Override
            public void handleMessage(Message msg) {
                MainActivity activity = weakReference.get();
                //Activity不存在了，就不需要再处理了
                if (activity == null) {
                    return;
                }
                //如果已经有消息了，先移除消息
                if (activity.handler.hasMessages(BANNER_NEXT)) {
                    activity.handler.removeMessages(BANNER_NEXT);
                }
                switch (msg.what) {
                    case BANNER_NEXT:
                        //跳到下一页，
                        int currentItem = vpBanner.getCurrentItem();
                        activity.vpBanner.setCurrentItem(++currentItem);
                        //5秒后继续轮播
                        activity.handler.sendEmptyMessageDelayed(BANNER_NEXT, 5000);
                        break;
                    case BANNER_PAUSE:
                        //暂停,不需要做任务操作
                        break;
                    case BANNER_RESUME:
                        //继续轮播
                        activity.handler.sendEmptyMessageDelayed(BANNER_NEXT, 5000);
                        break;
                }
            }
        }

### 在Activity中使用 ###

//这里放了3张图片，使用Gilde加载
            ImageView imageView1 = new ImageView(this);
            ImageView imageView2 = new ImageView(this);
            ImageView imageView3 = new ImageView(this);
            RequestManager requestManager = Glide.with(this);
            requestManager.load("http://img1.imgtn.bdimg.com/it/u=3251910782,1174316217&fm=21&gp=0.jpg").into(imageView1);
            requestManager.load("http://pic2.ooopic.com/10/78/50/34b1OOOPICf0.jpg").into(imageView2);
            requestManager.load("http://www.swkweike.com/data/uploads/2015/08/18/193226787255d2dbd711a33.jpg").into(imageView3);
            List<ImageView> list = new ArrayList<>();
            list.add(imageView1);
            list.add(imageView2);
            list.add(imageView3);
            MyPagerAdapter adapter = new MyPagerAdapter(this, list);
            vpBanner = (ViewPager) findViewById(R.id.vpBanner);
            vpBanner.setAdapter(adapter);
            //将起始位置设置在中间，让用户看不到边界
            vpBanner.setCurrentItem(Integer.MAX_VALUE / 2);
            //开始轮播
            handler.sendEmptyMessageDelayed(BANNER_NEXT, 5000);

### 用户滑动时停止轮播,松开时继续轮播 ###

使用ViewPager的滑动监听事件，判断用户是否正在滑动

vpBanner.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
                @Override
                public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
    
                }
    
                @Override
                public void onPageSelected(int position) {
    
                }
    
                @Override
                public void onPageScrollStateChanged(int state) {
                    switch (state) {
                        case ViewPager.SCROLL_STATE_DRAGGING:
                            //用户正在滑动，暂停轮播
                            handler.sendEmptyMessage(BANNER_PAUSE);
                            break;
                        case ViewPager.SCROLL_STATE_IDLE:
                            //滑动结束，继续轮播
                            handler.sendEmptyMessageDelayed(BANNER_NEXT, 5000);
                            break;
                    }
    
                }
            });