android怎么实现轮播图片

Android中可以使用ViewPager和PagerAdapter来实现轮播图片功能。

首先，在布局文件中添加ViewPager控件：

```xml

android:id="@+id/viewPager"

android:layout_width="match_parent"

android:layout_height="200dp"/>

```

然后，创建Adapter类继承自PagerAdapter，并重写以下方法：

```java

public class ViewPagerAdapter extends PagerAdapter {

private Context mContext;

private List mImageList;

public ViewPagerAdapter(Context context, List imageList) {

mContext = context;

mImageList = imageList;

}

@Override

public int getCount() {

return mImageList.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 imageView = new ImageView(mContext);

imageView.setImageResource(mImageList.get(position));

imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);

container.addView(imageView);

return imageView;

}

@Override

public void destroyItem(@NonNull ViewGroup container, int position, @NonNull Object object) {

container.removeView((View) object);

}

}

```

接下来，在Activity中使用Adapter和ViewPager：

```java

public class MainActivity extends AppCompatActivity {

private ViewPager mViewPager;

private ViewPagerAdapter mAdapter;

private List mImageList;

@Override

protected void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

mViewPager = findViewById(R.id.viewPager);

// 添加图片资源

mImageList = new ArrayList<>();

mImageList.add(R.drawable.image1);

mImageList.add(R.drawable.image2);

mImageList.add(R.drawable.image3);

mAdapter = new ViewPagerAdapter(this, mImageList);

mViewPager.setAdapter(mAdapter);

// 开启自动轮播

startAutoPlay();

}

private void startAutoPlay() {

Timer timer = new Timer();

timer.schedule(new TimerTask() {

@Override

public void run() {

runOnUiThread(new Runnable() {

@Override

public void run() {

int currentItem = mViewPager.getCurrentItem();

mViewPager.setCurrentItem((currentItem + 1) % mImageList.size());

}

});

}

}, 2000, 2000);

}

}

```

以上代码中，我们通过mImageList来保存要轮播的图片资源，在ViewPager的Adapter中将图片资源设置给ImageView显示。通过Timer和定时任务实现自动轮播，每隔一定时间就切换ViewPager的显示页面。