android studio使用ViewPager实现轮播图

要使用 ViewPager 实现轮播图，需要遵循以下几个步骤：

1.在布局文件中添加 ViewPager 组件和指示器组件（如小圆点）。

<androidx.viewpager.widget.ViewPager
    android:id="@+id/viewPager"
    android:layout_width="match_parent"
    android:layout_height="200dp"/>

<LinearLayout
    android:id="@+id/indicatorLayout"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="horizontal"
    android:gravity="center"/>

2.创建适配器类，继承自 ViewPager.Adapter，并实现 getCount()、instantiateItem()、destroyItem()、isViewFromObject() 等方法。

public class ViewPagerAdapter extends PagerAdapter {
    private Context mContext;
    private int[] mImageIds;

    public ViewPagerAdapter(Context context, int[] imageIds) {
        mContext = context;
        mImageIds = imageIds;
    }

    @Override
    public int getCount() {
        return mImageIds.length;
    }

    @Override
    public Object instantiateItem(ViewGroup container, int position) {
        ImageView imageView = new ImageView(mContext);
        imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
        imageView.setImageResource(mImageIds[position]);
        container.addView(imageView);
        return imageView;
    }

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

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

3.在 Activity 或 Fragment 中设置 ViewPager 的适配器，并为其添加一个 OnPageChangeListener 监听器，用于实现指示器的更新。

ViewPager viewPager = findViewById(R.id.viewPager);
int[] imageIds = {R.drawable.image1, R.drawable.image2, R.drawable.image3};
ViewPagerAdapter adapter = new ViewPagerAdapter(this, imageIds);
viewPager.setAdapter(adapter);

LinearLayout indicatorLayout = findViewById(R.id.indicatorLayout);
for (int i = 0; i < imageIds.length; i++) {
    ImageView imageView = new ImageView(this);
    imageView.setImageResource(R.drawable.indicator_normal);
    indicatorLayout.addView(imageView);
}

final int indicatorCount = indicatorLayout.getChildCount();
viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
    @Override
    public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
    }

    @Override
    public void onPageSelected(int position) {
        for (int i = 0; i < indicatorCount; i++) {
            ImageView imageView = (ImageView) indicatorLayout.getChildAt(i);
            if (i == position) {
                imageView.setImageResource(R.drawable.indicator_selected);
            } else {
                imageView.setImageResource(R.drawable.indicator_normal);
            }
        }
    }

    @Override
    public void onPageScrollStateChanged(int state) {
    }
});

这样就可以实现一个基本的 ViewPager 轮播图，并在指示器中显示当前页码。