轮播图是 Android 常用功能之一，效果大概是这样的：

之前我封装写了一个，基本达到了要求，是继承了 Fragment（当时脑袋肯定锈掉了），里面 Viewpager add Fragment，这次项目多处有轮播图，发现之前封装的不够用，简直漏洞百出：1、比如底部 point 的位置，之前固定在中间，现在可能要放在右下角，point 最好也能动态改图片；2、现在项目跟微信一样，底部 tab 切换，中间是 Fragment 替换，发现轮播图有问题，Fragment A 循环的 point 的 positoin 居然影响到了 Fragment B，照理，这是两个 BannerFragment，不会影响的啊，报以下错误：

java.lang.IllegalStateException: The application's PagerAdapter changed the adapter's
contents without calling PagerAdapter#notifyDataSetChanged!

经过排查，找到了原因，因为 Viewpager add Fragment 我全部放在一个类，因此：

public static List<Object> bannerList = new ArrayList<>();

这里 static 坏事了，之前一个 banner 没有暴露出来。3、继承了 Fragment，引用比较麻烦，Fragment 有两者引用方法，xml 和代码，两者方式 addData 却报错；4、banner 没有写点击回调。

再次封装

综合以上问题，我进行了优化，继承 LinearLayout，当一个控件来引用，省去不必要的麻烦，底部 point 的位置可以设置：

pointLayout.setGravity(bannerPointGravity);

另外自定义了属性，动态设置 point 大小和图片，轮播图循环时间，也能代码设置，完整代码示例：

 * Created by WuXiaolong on 2017/8/24.* 个人博客：http：//wuxiaolong.me*/public class BannerLayout extends LinearLayout {private ViewPager viewPager;private LinearLayout pointLayout;private ScheduledExecutorService scheduler;private int mPosition = 0;private int mBannerCount = 1;private Context context;private Activity activity;private int bannerPointSize;private int bannerPointGravity;private int bannerPointDrawableSelected, bannerPointDrawableUnselected;private int bannerDelaySecond;public BannerLayout(Context context) {this(context, null);}public BannerLayout(Context context, @Nullable AttributeSet attrs) {this(context, attrs, 0);}public BannerLayout(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {super(context, attrs, defStyleAttr);initView(context, attrs);}private void initView(Context context, AttributeSet attrs) {this.context = context;activity = (Activity) context;TypedArray typedArray = context.obtainStyledAttributes(attrs, R.styleable.BannerLayout);bannerPointSize = typedArray.getDimensionPixelSize(R.styleable.BannerLayout_bannerPointSize, 10);bannerPointGravity = typedArray.getInt(R.styleable.BannerLayout_bannerPointGravity, Gravity.CENTER);bannerDelaySecond = typedArray.getInt(R.styleable.BannerLayout_bannerDelaySecond, 5);bannerPointDrawableSelected = typedArray.getResourceId(R.styleable.BannerLayout_bannerPointDrawableSelected, R.mipmap.point01);bannerPointDrawableUnselected = typedArray.getResourceId(R.styleable.BannerLayout_bannerPointDrawableUnselected, R.mipmap.point02);typedArray.recycle();View view = View.inflate(context, R.layout.banner_view_pager, null);addView(view);viewPager = (ViewPager) view.findViewById(R.id.viewPager);pointLayout = (LinearLayout) view.findViewById(R.id.pointLayout);pointLayout.setGravity(bannerPointGravity);viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {@Overridepublic void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {}@Overridepublic void onPageSelected(int position) {addPointLayout(position);}@Overridepublic void onPageScrollStateChanged(int state) {}});}public void start(List<Object> bannerList) {bannerShutdown();mBannerCount = bannerList.size();BannerPagerAdapter bannerPagerAdapter = new BannerPagerAdapter(context, bannerList);viewPager.setAdapter(bannerPagerAdapter);addPointLayout(0);startScheduler();}private void addPointLayout(int position) {pointLayout.removeAllViews();for (int i = 0; i < mBannerCount; i++) {ImageView imageView = new ImageView(context);LinearLayout.LayoutParams layoutParams = new LinearLayout.LayoutParams(bannerPointSize, bannerPointSize);layoutParams.setMargins(10, 0, 0, 0);imageView.setLayoutParams(layoutParams);if (position == i) {imageView.setImageResource(bannerPointDrawableSelected);} else {imageView.setImageResource(bannerPointDrawableUnselected);}pointLayout.addView(imageView);}}private void startScheduler() {scheduler = Executors.newSingleThreadScheduledExecutor();scheduler.scheduleAtFixedRate(new Runnable() {@Overridepublic void run() {mPosition = viewPager.getCurrentItem();if (mPosition < mBannerCount - 1) {mPosition++;} else {mPosition = 0;}activity.runOnUiThread(new Runnable() {@Overridepublic void run() {viewPager.setCurrentItem(mPosition);}});}}, 1, bannerDelaySecond, TimeUnit.SECONDS);}public void bannerShutdown() {if (scheduler != null)scheduler.shutdown();}private class BannerPagerAdapter extends PagerAdapter {private List<Object> bannerList = new ArrayList<>();private Context context;BannerPagerAdapter(Context context, List<Object> bannerList) {this.context = context;this.bannerList.clear();this.bannerList.addAll(bannerList);}@Overridepublic int getCount() {return bannerList.size();}@Overridepublic boolean isViewFromObject(View view, Object object) {return view == object;}@Overridepublic Object instantiateItem(ViewGroup container, final int position) {ImageView imageView = new ImageView(context);imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);Object object = bannerList.get(position);//这里我封装了 Glide 4.0 的工具类，用于显示图片ImageLoaderUtil.load(context, object, imageView);container.addView(imageView);return imageView;}@Overridepublic void destroyItem(ViewGroup container, int position, Object object) {container.removeView((View) object);}}public int dp2px(float var0) {float var1 = context.getResources().getDisplayMetrics().density;return (int) (var0 * var1 + 0.5F);}public void setBannerPointSize(int bannerPointSize) {this.bannerPointSize = dp2px(bannerPointSize);}public void setBannerPointGravity(int bannerPointGravity) {this.bannerPointGravity = bannerPointGravity;pointLayout.setGravity(bannerPointGravity);}public void setBannerPointDrawableSelected(int bannerPointDrawableSelected) {this.bannerPointDrawableSelected = bannerPointDrawableSelected;}public void setBannerPointDrawableUnselected(int bannerPointDrawableUnselected) {this.bannerPointDrawableUnselected = bannerPointDrawableUnselected;}public void setBannerDelaySecond(int bannerDelaySecond) {this.bannerDelaySecond = bannerDelaySecond;}}

其中自定义属性的attrs.xml：

<resources><declare-styleable name="BannerLayout"><!--轮播图点的大小--><attr name="bannerPointSize" format="dimension" /><!--轮播图点的位置，分别有左中右--><attr name="bannerPointGravity" format="enum"><enum name="left" value="3" /><enum name="center" value="17" /><enum name="right" value="5" /></attr><!--轮播图点选中的图片--><attr name="bannerPointDrawableSelected" format="reference" /><!--轮播图点未选中的图片--><attr name="bannerPointDrawableUnselected" format="reference" /><!--轮播图循环时间，单位秒--><attr name="bannerDelaySecond" format="integer" /></declare-styleable>
</resources>

使用说明

xml

<com.wuxiaolong.bannersample.BannerLayoutandroid:id="@+id/bannerView"android:layout_width="match_parent"android:layout_height="198dp"app:bannerDelaySecond="3"app:bannerPointDrawableSelected="@drawable/gray_radius"app:bannerPointDrawableUnselected="@drawable/white_radius"app:bannerPointGravity="right"app:bannerPointSize="10dp" />

调用：

public class MainActivity extends AppCompatActivity {private BannerLayout bannerView;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);bannerView = (BannerLayout) findViewById(R.id.bannerView);List<Object> bannerList = new ArrayList<>();bannerList.add(R.mipmap.horizontal_default);bannerList.add("http://pic1.win4000.com/wallpaper/5/598161750eddb.jpg");bannerList.add("http://pic1.win4000.com/wallpaper/4/597efb5b6aae8.jpg");bannerView.setBannerPointSize(10);bannerView.setBannerPointGravity(Gravity.CENTER);bannerView.setBannerPointDrawableSelected(R.drawable.gray_radius);bannerView.setBannerPointDrawableUnselected(R.mipmap.point01);bannerView.setBannerDelaySecond(5);//banner 设置方法完毕时最后调用 start 方法bannerView.start(bannerList);}@Overrideprotected void onStop() {super.onStop();bannerView.bannerShutdown();}
}

最后

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