本文是基于ViewPager实现的无限自动轮播banner，供大家参考，具体内容如下
分为四步去实现：
第一步是有限手动轮播；
第二步是无限轮播；
第三步是自动轮播；
第四步是指示器适配
第一步：有限手动轮播实现
布局：
<androidx.viewpager.widget.ViewPager
android:id="@+id/banner"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginStart="12dp"
android:layout_marginEnd="12dp" />
adapter实现：
public class BannerAdapter extends PagerAdapter {
private List<String> bannerList;
public BannerAdapter(List<String> bannerList) {
this.bannerList = bannerList;
}
@Override
public int getCount() {
return bannerList.size();
}
@Override
public boolean isViewFromObject(@NonNull View view, @NonNull Object object) {
return view == object;
}
@NonNull
@Override
public Object instantiateItem(@NonNull ViewGroup container, int position) {
ImageView bannerImageView = new ImageView(container.getContext());
ViewGroup.LayoutParams lp = new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT);
bannerImageView.setLayoutParams(lp);
bannerImageView.setScaleType(ImageView.ScaleType.FIT_XY);
Glide.with(container.getContext()).load(bannerList.get(position)).into(bannerImageView);
container.addView(bannerImageView);
return bannerImageView;
}
@Override
public void destroyItem(@NonNull ViewGroup container, int position, @NonNull Object object) {
container.removeView((View) object);
}
}
Activity中：
// scrollview中viewpager一定要设置高度，此处根据图片的宽高比来设定高度
int bannerWidth = (Utils.getScreenWidth(getContext()) - Utils.dip2pixel(getContext(), 24));
LinearLayout.LayoutParams lp = (LinearLayout.LayoutParams) bannerView.getLayoutParams();
lp.width = LinearLayout.LayoutParams.MATCH_PARENT;
lp.height = (int) (bannerWidth * 90f / 345);
bannerView.setLayoutParams(lp);
bannerView.setAdapter(new BannerAdapter(getUrlList()));
注意：ScrollView包裹ViewPager时，ViewPager的高度一定要有确定值，否则内容无法加载出来，可以在xml中指定，也可以代码设定，但一定要有确定值。
第二步：无限轮播
无限轮播只需要在有限轮播的基础上，做以下两个改动点，修改getCount返回值且在加载数据时获取正确的数据源即可
public class BannerAdapter extends PagerAdapter {
private List<String> bannerList;
public BannerAdapter(List<String> bannerList) {
this.bannerList = bannerList;
}
@Override
public int getCount() {
// return bannerList.size(); // before
return Integer.MAX_VALUE; // now
}
@Override
public boolean isViewFromObject(@NonNull View view, @NonNull Object object) {
return view == object;
}
@NonNull
@Override
public Object instantiateItem(@NonNull ViewGroup container, int position) {
ImageView bannerImageView = new ImageView(container.getContext());
int realPosition = position % bannerList.size(); // 获取要加载数据的真实位置
ViewGroup.LayoutParams lp = new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT);
bannerImageView.setLayoutParams(lp);
bannerImageView.setScaleType(ImageView.ScaleType.FIT_XY);
// Glide.with(container.getContext()).load(bannerList.get(position)).into(bannerImageView); // before
Glide.with(container.getContext()).load(bannerList.get(realPosition)).into(bannerImageView); // now
container.addView(bannerImageView);
return bannerImageView;
}
@Override
public void destroyItem(@NonNull ViewGroup container, int position, @NonNull Object object) {
container.removeView((View) object);
}
}
修改完发现banner只能向右无限轮播，第一次左滑滑不动，这个时候我们强制设置viewpager位置在中间就可以解决这个问题了
bannerView.setAdapter(new BannerAdapter(getUrlList()));
bannerView.setCurrentItem(getUrlList().size() * 5);
第三步：自动轮播
handler每隔轮播间隔发送消息，设置viewpager为下一个位置
private Runnable bannerRunnable = new Runnable() {
@Override
public void run() {
bannerView.setCurrentItem(bannerView.getCurrentItem() + 1);
mHandler.postDelayed(bannerRunnable, 3000);
}
};
bannerView.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
}
@Override
public void onPageSelected(int position) {
// 手滑动到某一位置，重新开始计时
start();
}
@Override
public void onPageScrollStateChanged(int state) {
}
});
private void start() {
mHandler.removeCallbacksAndMessages(null);
mHandler.postDelayed(bannerRunnable, 3000);
}
第四步：添加指示器
指示器样式及表现可以自己去根据需求实现，以相对简单和常见的小圆圈指示器为例，添加和banner数量相同的小圆圈，小圆圈设置selector，在选中时为黑色选中样式，在非选中时为灰色默认样式，根据当前选中的banner的实际position，设置指示器的selected属性，从而展示不同的样式
private void initIndicator() {
for (int i = 0; i < getUrlList().size(); i++) {
View view = new View(getActivity());
LinearLayout.LayoutParams lp = new LinearLayout.LayoutParams(Utils.dip2pixel(getActivity(), 6), Utils.dip2pixel(getActivity(), 6));
lp.rightMargin = Utils.dip2pixel(getActivity(), 8);
view.setLayoutParams(lp);
view.setBackgroundResource(R.drawable.selector_indicator_view);
view.setSelected(i == 0);
llIndicatorView.addView(view);
}
}
private void initBannerView() {
bannerView.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
}
@Override
public void onPageSelected(int position) {
// 手滑动到某一位置，重新开始计时
realPosition = 0;
realPosition = position % getUrlList().size();
// 根据当前滑动到的banner设置指示器的状态
for (int i = 0; i < llIndicatorView.getChildCount(); i++) {
llIndicatorView.getChildAt(i).setSelected(i == realPosition);
}
start();
}
@Override
public void onPageScrollStateChanged(int state) {
}
});
}
附：Utils文件
public class Utils {
public static void setFullScreen(Activity activity) {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
ViewGroup decorView = (ViewGroup) activity.getWindow().getDecorView();
decorView.setSystemUiVisibility(View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN | View.SYSTEM_UI_FLAG_LIGHT_STATUS_BAR);
activity.getWindow().setStatusBarColor(Color.TRANSPARENT);
}
}
public static int dip2pixel(Context context, float n) {
int value = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, n, context.getResources().getDisplayMetrics());
return value;
}
/**
* 获取屏幕宽度
* @param context
* @return 屏幕宽度
*/
public static int getScreenWidth(Context context) {
WindowManager wm = (WindowManager) context
.getSystemService(Context.WINDOW_SERVICE);
DisplayMetrics outMetrics = new DisplayMetrics();
wm.getDefaultDisplay().getMetrics(outMetrics);
return outMetrics.widthPixels;
}
}
