广告轮播控件越来越常见，大都使用viewpager来承载广告图片，见于实在是太常用了，因此今天决定将其封装成一个组件，方便日后使用。本组件集成于一个FrameLayout,其中使用viewpager来显示图片，LinearLayout来显示小圆点指示器（也有有直接在图片上做好指示器的，这个实在是太难维护）。 【详细代码见gitHub，欢迎交流，请多多指教】

</br>

bannerview.gif

1、组件布局（custom_banner_layout.xml ）

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <android.support.v4.view.ViewPager
        android:id="@+id/view_pager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:unselectedAlpha="1"></android.support.v4.view.ViewPager>
    <LinearLayout
        android:id="@+id/bannerPage"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_gravity="center|bottom"
        android:gravity="center"
        android:orientation="horizontal"
        android:background="#60000000"
        android:padding="10dip"></LinearLayout>
</FrameLayout>

2、核心代码 BannerView编码(代码比较简单，不做详细讲解，代码中注释也比较详细)

/**
 * Created by david on 2016/9/23.
 */
public class BannerView extends FrameLayout implements ViewPager.OnPageChangeListener {

    /**
     * 广告url集合，这里不加修饰文案，因此直接放一个url
     * 如果需要加入文字信息，自行封装为javaBean
     */
    private List<String> urls;
    private Context context;
    private ViewPager viewPager;

    /**
     * 存放圆点指示器
     */
    private LinearLayout bannerPage;

    private PagerAdapter adapter;

    /**
     * 用户手动滑动广告中
     */
    private boolean isScrollingByUser;

    /**
     * 轮播切换小圆点宽度默认宽度
     */

    private int IndicatorDotWidth;

    /**
     * 当前页pos
     */
    private int currentPosition = 0;

    /**
     * 历史页pos
     */
    private int prePosition = 0;

    /**
     * 轮播图总数
     */
    private int count;

    /**
     * 定时滚动相关
     */
    private Timer timer;
    private TimerTask task;


    private Handler handler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            int what = msg.what;
            switch (what) {
                case 0:
                    LogUtil.e("info","what == 0");
                    if (viewPager != null && !isScrollingByUser) {
                        currentPosition++;
                        viewPager.setCurrentItem(currentPosition);
                    }
                    break;
            }
        }
    };
    private BannerOnClickListener onClickListener;

    public BannerView(Context context) {
        super(context);
        this.context = context;
    }

    public BannerView(Context context, AttributeSet attrs) {
        super(context, attrs);
        this.context = context;
    }

    public BannerView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    private void init() {
        LogUtil.e("info", "init");
        if (adapter == null) {
            return;
        }
        viewPager.setAdapter(adapter);
        /**
         * viewpager 切换动画
         */
        viewPager.setPageTransformer(true,new MyPageTransformer());
        bannerPage.removeAllViews();

        /**
         * 向线性布局中添加小圆点指示器
         * */
        View dot;
        LinearLayout.LayoutParams params;
        for (int i = 0; i < count; i++) {
            dot = new View(context);
            params = new LinearLayout.LayoutParams(IndicatorDotWidth, IndicatorDotWidth);
            params.setMargins(IndicatorDotWidth, 0, 0, 0);
            dot.setLayoutParams(params);
            dot.setBackgroundResource(R.drawable.dot_bg_selector);
            dot.setEnabled(false);//默认设为非选中
            bannerPage.addView(dot);
        }
        int midPosition = Integer.MAX_VALUE / 2 - Integer.MAX_VALUE / 2 % count;
        currentPosition = midPosition;
        bannerPage.getChildAt(0).setEnabled(true);
        viewPager.setCurrentItem(midPosition);// 设置item 一定要放在圆点初始化之后，否则 onPageSelected（） 会报空指针异常
    }

    @Override
    protected void onFinishInflate() {
        super.onFinishInflate();
        IndicatorDotWidth =  dip2px(context,5);
        View view = LayoutInflater.from(context).inflate(R.layout.custom_banner_layout, null);
        viewPager = (ViewPager) view.findViewById(R.id.view_pager);
        bannerPage = (LinearLayout) view.findViewById(R.id.bannerPage);
        viewPager.addOnPageChangeListener(this);
        addView(view);
    }

    public void setData(List<String> urls) {

       if (urls.isEmpty()) {  
             return;
        }
        this.urls = urls;
        count = urls.size();
        if (adapter == null) {
            adapter = new MyAdapter(urls);
        }
        init();
    }


    public void startBannerScrollTask(long timeSpace) {
        if (count == 0){  
            return;
         }
        //true 说明这个timer以daemon方式运行（优先级低，程序结束timer也自动结束）
        timer = new Timer(true);
        task = new TimerTask() {
            @Override
            public void run() {
                handler.sendEmptyMessage(0);
            }
        };

        timer.schedule(task, 1000, timeSpace);//1000ms后按指定时间间隔轮播
    }

    public void stopBannerTask() {
        if (task != null) {
            task.cancel();
        }
    }


    @Override
    public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
    }

    @Override
    public void onPageSelected(int position) {
        currentPosition = position;
        bannerPage.getChildAt(prePosition % urls.size()).setEnabled(false);
        bannerPage.getChildAt(currentPosition % urls.size()).setEnabled(true);// 设置true放后面  防止初始化时 两个pos都为0时  没有默认选中
        prePosition = currentPosition;
    }

    @Override
    public void onPageScrollStateChanged(int state) {
        /**
         * 用户手动滑动广告时，取消自动翻页相应
         */
        if (state == 0) {
            isScrollingByUser = false;
        } else//用户手动滑动中
            isScrollingByUser = true;

    }


    class MyAdapter extends PagerAdapter {
        List<String> adUrls;

        public MyAdapter(List<String> adUrls) {
            this.adUrls = adUrls;
        }

        @Override
        public int getCount() {

            return Integer.MAX_VALUE;
        }

        @Override
        public Object instantiateItem(ViewGroup container, final int position) {
            ImageView imageView = new ImageView(context);
            String currentUrl = adUrls.get(position % adUrls.size());
            imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
            ImageLoaderUtil.setImageWithCache(currentUrl, imageView);

            if(onClickListener != null){
                imageView.setOnClickListener(new OnClickListener() {
                    @Override
                    public void onClick(View view) {
                        onClickListener.onClickListener(position % adUrls.size());
                    }
                });
            }
            container.addView(imageView);

            return imageView;
        }

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

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

    class MyPageTransformer implements ViewPager.PageTransformer{
        @Override
        public void transformPage(View page, float position) {

            /**
             * 尺寸变化
             */
//            float normalizedposition = Math.abs(Math.abs(position) - 1);
//            page.setScaleX(normalizedposition / 2 + 0.5f);
//            page.setScaleY(normalizedposition / 2 + 0.5f);

            /**
             * 淡入淡出
             */
            final float normalizedposition = Math.abs(Math.abs(position) - 1);
            page.setAlpha(normalizedposition);
        }
    }
    /**
     * 根据手机的分辨率从 dip 的单位 转成为 px(像素)
     */
    public static int dip2px(Context context, float dpValue) {
        final float scale = context.getResources().getDisplayMetrics().density;
        return (int) (dpValue * scale + 0.5f);
    }

    public void setOnClickListener(BannerOnClickListener onClickListener){
        this.onClickListener = onClickListener;
    }
    public interface BannerOnClickListener{
        void onClickListener(int pos);
    }
}

3-1、使用起来非常简单，首先在activity_main.xml中加入对应组件

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <com.david.bannerviewdemo.custom.BannerView
        android:id="@+id/bannerView"
        android:layout_width="match_parent"
        android:layout_height="300dp">

    </com.david.bannerviewdemo.custom.BannerView>
</RelativeLayout>

3-2、MainActivity.class，接入数据以及设置回调接口即可，十分方便。

public class MainActivity extends AppCompatActivity {
    private BannerView bannerView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        bannerView = (BannerView) findViewById(R.id.bannerView);

        List<String> urls = new ArrayList<>();
        urls.add("http://img.zcool.cn/sucaiori/733B8D1B-4140-8B0C-EF86-CC6C6793D072.jpg@700w_0e_1l.jpg");
        urls.add("http://img.zcool.cn/sucaiori/BB0E9E48-9B9B-AC2B-EEB5-198391F8CC1A.jpg@700w_0e_1l.jpg");
        urls.add("http://img.zcool.cn/sucaiori/8BD5E2A8-52E7-18D5-D77B-E50DFFD5EEA4.jpg@700w_0e_1l.jpg");

        bannerView.setData(urls);
        bannerView.setOnClickListener(new BannerView.BannerOnClickListener() {
            @Override
            public void onClickListener(int pos) {
                Toast.makeText(MainActivity.this, "" + pos, Toast.LENGTH_SHORT).show();
            }
        });
    }


    @Override
    protected void onResume() {
        super.onResume();
        bannerView.startBannerScrollTask(2000);//开启滚动
    }

    @Override
    protected void onStop() {
        super.onStop();
        bannerView.stopBannerTask();
    }
}