Android 使用ViewPager和自定义PagerAdapter实现轮播图效果

Posted 2021-12-12 路宇

一、首先是布局页面activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="200dp"
    android:background="#DFDFDF"
    tools:context=".MainActivity">

    <androidx.viewpager.widget.ViewPager
        android:id="@+id/viewPager"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="@color/white" />

    <LinearLayout
        android:id="@+id/viewGroup"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_centerHorizontal="true"
        android:layout_marginBottom="3dp"
        android:orientation="horizontal" />
</RelativeLayout>

二、自定义MyPagerAdapter类继承与PagerAdapter

public class MyPagerAdapter extends PagerAdapter {
    private int[] banners = new int[]{R.mipmap.banner_one, R.mipmap.banner_two, R.mipmap.banner_three};
    private Context context;
    private View.OnClickListener onBannerClickListener;
    private static final String TAG = "MyPagerAdapter";

    public MyPagerAdapter(Context context) {
        this.context = context;
    }

    @Override
    public int getCount() {
    	//返回int的最大值 可以一直滑动
        return Integer.MAX_VALUE;
    }

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

    @NonNull
    @Override
    public Object instantiateItem(@NonNull ViewGroup container, int position) {
        Log.e(TAG, "instantiateItem1: " + position);
        position %= banners.length;
        Log.e(TAG, "instantiateItem2: " + position);
        ImageView imageView = new ImageView(context);
        //设置图片缩放类型
        imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
        //把当前的下标通过setTag方法设置进去
        imageView.setTag(position);
        imageView.setImageResource(banners[position]);
        imageView.setOnClickListener(onClickListener);
        container.addView(imageView);
        return imageView;
    }

    private View.OnClickListener onClickListener = new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            onBannerClickListener.onClick(v);
        }
    };

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

    public void setOnBannerClickListener(View.OnClickListener onBannerClickListener) {
        this.onBannerClickListener = onBannerClickListener;
    }

    public int[] getBanners() {
        return banners;
    }
}

三、MainActivity.java代码如下，注释已经在代码中给出

public class MainActivity extends AppCompatActivity {
    private static final String TAG = "MainActivity";
    private MyPagerAdapter myPagerAdapter;
    private ViewPager viewPager;
    private LinearLayout viewGroup;

    private int currentItem = 0;
    private final Handler handler = new Handler();
    private static final int CAROUSEL_TIME = 3000;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        viewPager = findViewById(R.id.viewPager);
        viewGroup = findViewById(R.id.viewGroup);
        myPagerAdapter = new MyPagerAdapter(this);
        myPagerAdapter.setOnBannerClickListener(onBannerClickListener);
        //设置缓存页数
        viewPager.setOffscreenPageLimit(myPagerAdapter.getBanners().length - 1);
        viewPager.setAdapter(myPagerAdapter);
        //添加页面更改监听器
        viewPager.addOnPageChangeListener(onPageChangeListener);

        //将点点的图添加到视图ViewGroup中
        for (int i = 0; i < myPagerAdapter.getBanners().length; i++) {
            ImageView imageView = new ImageView(this);
            //设置图片的宽高 为10像素
            imageView.setLayoutParams(new ViewGroup.LayoutParams(10, 10));
            if (i == 0) {
                //第一个为默认选中状态
                imageView.setImageResource(R.drawable.icon_page_select);
            } else {
                imageView.setImageResource(R.drawable.icon_page_normal);
            }
            LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT, ViewGroup.LayoutParams.WRAP_CONTENT);
            params.leftMargin = 5;
            params.rightMargin = 5;
            viewGroup.addView(imageView, params);
        }
        //给ViewPager设置当前页，这样刚打开软件也能向左滑动
        currentItem = myPagerAdapter.getBanners().length * 50;
        viewPager.setCurrentItem(currentItem);
        handler.postDelayed(mTicker, CAROUSEL_TIME);
    }

    private final Runnable mTicker = new Runnable() {
        @Override
        public void run() {
            long now = SystemClock.uptimeMillis();
            Log.d(TAG, "now:" + now);
//            long next = now + (CAROUSEL_TIME - now % CAROUSEL_TIME);
            //等同于
            long next = now + CAROUSEL_TIME;
            Log.d(TAG, "next: " + next);
            //回调应该运行的绝对时间 3秒后发送消息
            handler.postAtTime(mTicker, next);
            currentItem++;
            viewPager.setCurrentItem(currentItem);
        }
    };

    private View.OnClickListener onBannerClickListener = new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            int position = (int) v.getTag();
            Toast.makeText(MainActivity.this, "当前点击位置：" + position, Toast.LENGTH_SHORT).show();
        }
    };

    private ViewPager.OnPageChangeListener onPageChangeListener = new ViewPager.OnPageChangeListener() {
        @Override
        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

        }

        @Override
        public void onPageSelected(int position) {
            Log.e(TAG, "onPageSelected: MainActivity" + position);
            currentItem = position;
            //当新页面选中时调用此方法，position 为新选中页面的位置索引
            //在所选页面的时候,点点图片也要发生变化
            setImageBackground(position %= myPagerAdapter.getBanners().length);
            Log.e(TAG, "onPageSelected: " + myPagerAdapter.getBanners().length);
        }

        @Override
        public void onPageScrollStateChanged(int state) {

        }
    };

    /**
     * 改变点点点的切换效果
     *
     * @param selectItem 当前选中的页面索引
     */
    private void setImageBackground(int selectItem) {
        for (int i = 0; i < myPagerAdapter.getBanners().length; i++) {
            ImageView imageView = (ImageView) viewGroup.getChildAt(i);
            imageView.setBackground(null);
            if (i == selectItem) {
                imageView.setImageResource(R.drawable.icon_page_select);
            } else {
                imageView.setImageResource(R.drawable.icon_page_normal);
            }
        }
    }
}

效果如图所示：